Wayne Norton
Digital Imaging Consultant
Video Engineer - HDCinematics
 

The Subject - "Getting the Most from your HD Video Camera
Calibration and Exposure Control"

"Getting the Most from your HD Video Camera Calibration and Exposure Control"

Using a DSC Chart

The great thing about the new Pro HD cameras is their ability to totally adjust the color matrix. Using the DSC color chip chart, tape measure, two equal light sources and Adobe OnLocation, Adobe Premiere Pro or Apple Final Cut Pro's built-in waveform monitors and vectorscopes, we will calibrate our camera to get the most color space possible. Most serious HD cameras have color matrix adjustments (check the user manual for your camera).

Adobe OnLocation is an excellent calibration tool - for use on initial camera matrix calibration as well as for on-set exposure control and monitoring. It is available in CS3, CS4 and CS5 versions. As these are important concepts I will go into some details of both camera matrix adjustment and on-set calibration and monitoring. We'll start with the waveform monitor and the white side of our DSC color chart. First we need to setup our calibration conditions as accurately as possible to get the most reliable results.

For calibration, I find it is best to move the chart to approx. 6 feet from the camera - straight on. Make sure to secure both the camera (locked down on tripod) and the chart so they do not move. I use a tape measure to place 2 identical diffused lights at an equal distance from the chart and aimed to illuminate the face of the chart evenly. If you see a lot of glare from the chart in the camera, tilt the chart slightly forward or backward to eliminate the majority of the glare - the DSC CamStand chart holder is designed for this. Be sure to have the chart fully in frame before calibration by using the charts handy framing registration markers. Zoom (or move your tripod) until the charts framing reference lines, line up with the edges of your viewfinder. After setting up the lights, turn the chart over to the white side (on custom two sided "white card" ChromaDuMondes - if not use the neutral gray background on the front as the point of reference). Your waveform monitor is a great way to gauge your lighting - it should show an almost straight line across the screen when your lighting is even and you have your exposure set properly (the gray bars on the other side of the chart will help us set our exposure correctly a little later). If not, it will show where the lighting is uneven- if there is a droop in the line on the left side of the screen, move the light on the left a little closer and retest - same story on the right side. The waveform monitor represents the light values it "sees" rather than painting a picture that your eyes readily recognize, each color represented by a number position on the waveform grid. This function will help us set our white and black values - a big step in obtaining proper exposure and grabbing all the light from the scene possible. Adjust the line produced by the white chart until it just touches the 100 line - now you have set your maximum white point to 100% - where it belongs - (see Example 1). (Note: Use the white chips on the front of the chart to set 100% white if you have a standard ChromaDuMonde - without the white card on the rear).

Example 2 - what you don't want to see!

Once you have your lights setup, before going any further it is necessary to white-balance to your lights (your camera manual will have information on how to white balance - and it should be done at any lighting change). Now it's time to turn the chart around to the color side. Your waveform monitor should now show a pattern similar to the image on the right. Pay close attention to the boxes at the top and bottom of the display - these are the white and black chips on the DSC chart and will guide us in setting up our exposure for the lighting and our bottom black level. The idea is to open the lens (adjust the f-stop or aperture setting) until the white boxes (the 4 boxes across the top of the waveform display) are just touching the 100 line. If after opening the lens all the way and ensuring your shutter is turned off* your white boxes still fall short of the 100 mark you need to add more light and re-adjust. After adjusting the white level check the waveform monitor for the 3 boxes at the bottom of the "X" (formed by the grayscale chips on the chart), and should be as close to the bottom line as possible. You should adjust your black level or master black level to bring the level to where it belongs. The closer these values are aligned on the waveform and vectorscope monitors, the better will be your color depth and saturation. You will notice a marked improvement in all of the footage you shoot - colors will pop out at you that were somewhat bland looking before and if you use the chart and the scopes before every setup you will always be assured of proper exposure and color control. Example 3 shows a properly exposed DSC chart - notice the white value at 100 and the black at 7.5 - now we have the full range of light in the scene available to record.

Once your master white and black levels are set, it's time to move on to the vectorscope. Here is where we will adjust our color matrix - phase, balance and gain. The vectorscope is set up with 6 boxes as targets - one each for red, magenta, blue, cyan, green and yellow. At the middle of the scope is white. The pattern in the middle of the scope is how the camera sees the colors on the DSC chart (the output signal for each of those colors). the Looking closely, each line emanating from the center represents of the scope display represents one of the same basic colors as are represented by the vectorscope boxes. The closer the ends of those lines are to being inside their respective color boxes, the closer the camera is to being properly calibrated. Looking at Example 4 you see the vectorscope representation of the DSC chart before any adjustment (using the cameras out of the box presets). We want the center of our 'star' pattern pretty much in the center of the vectorscope display we are done, and the ends of each color line in each of their respective boxes. Looking at Example 4, the pattern is not too bad, but the star pattern is visibly off-center and the lines are not anywhere near to their color boxes. Now it is time to make adjustments. Refer to your camera manual and locate the color matrix (correction) adjustments and controls and become familiar with them, they are the key to any successful camera color calibration! These controls vary drastically from camera-to-camera so the best thing is to get setup with your chart and experiment with each setting while observing the resulting changes on your scope. You will see that almost any adjustment you make will have an effect on all of the other colors as well as the phase (rotation of the star pattern) of the colors. As you adjust for red, your green suffers, and vice-versa. With an appropriate amount of time, and the power of the vectorscope and chart, you should be able to get your colors better on target and much more vibrant with increased saturation. This will require some trial-and-error, but your target goal is clear and obtainable.

Example 5 shows the same setup after a quick tweaking - not perfect but much closer with a lot better color depth. There is a point of over-saturation so watch your output monitor in OnLocation for obvious signs of over-doing it. Your chart should look bright, color accurate and rich when your camera is properly calibrated. Your footage will look it's absolute best and provide your post production staff with the easiest media to work with.

Why bother? Well, the new HD cameras are nice, but without spending tens of thousands of dollars, they are not quite as good as 35mm film cameras for resolution. If you want your output to look as good as film you will already start off handicapped by that fact. In order to get the best quality output you need the best quality input - that means recording as much of the real color space as possible. This is probably the only way to do so. After learning these techniques, my on set calibration and setup time is minimal, my results are predictable and reliable, colors are vibrant and look great - and the footage is easy to work with - the less color correction you require in post production the better! There are many more details to follow related to this subject in following chapters and articles. For now I hope I have given you enough info to get your camera shooting at its best...

* if you do not have a shutter 'off' setting set as follows - for 30fps use 1/60th second shutter speed - for 24fps use 1/48th second shutter speed. Otherwise keep the shutter off unless using for slow-motion or fast action sequences.

DSC's November TechTip
comes from

Gary Adcock
Stereographer, Instructor
 

The Subject - "Real World Use of DSC's Fairburn 3-D Chart"

 

DSC's September TechTip
comes from

John Sharaf
John Sharaf Photography

The Subject - "Exposure for Sony S-Log with New DSC Chart"

One of the most compelling reasons to use the Sony SRW9000, F23 or F35 is the Sony Log Curve feature, also known as "S-Log".  This allows extended dynamic range of twelve stops vs. a more typical range of 8 stops in a conventional 709 picture.  Of course it's the ability to record 10-bit depth on the accompanying HDCAM-SR recorder (either the attached SRW-1 or the on-board SRW9000) allowing non-destructive color correction in post-production that completes the required work-flow.

Making the proper exposure for the log curve on a consistent basis is the main hurdle for the digital cinematographer. These cameras help by providing a readout of the ASA based on the gain setting on a display on the operator's side of the camera. Nominally the SRW9000 is 960ASA at the +6Db setting which allows the maximum 800% Dynamic Range, and the latest software on the F35 offers 800ASA at 0Db. Knowing and trusting the ASA encourages the use of an exposure meter for lighting and setting the exposure, and makes the whole experience more like shooting film. The use of DSC's prototype "S-Log Chart" allows both great confidence in confirming the stated speed and/or setting the exposure with the aid of a waveform or even by the cameras' internal zebras.

The S-Log Chart consists of a large 50% mid-gray field around a smaller 90% white chip, similar to what you'd find on a conventional chip chart but with  much larger targets for the purpose of reading the exposure on a waveform monitor or the zebras in a viewfinder.  In the S-Log mode, mid-gray should be set to 38% on the scope and the white chip at 68%. This creates a somewhat compressed picture while allowing "head-room" above the white for objects found in the real world that are essentially "brighter" than white. With the chart, a camera set to S-Log, an incident lightmeter and a waveform monitor you have everything you need to confirm the speed and set the proper exposure.  Read the incident exposure on a flatly lit chart, either in an engineering environment or the real world, set the lens iris appropriately, and then note that the resulting waveform puts the middle gray and white where it belongs; this confirms the correctness of the system. Furthermore, because these camera also have built in LUT's to convert the monitoring output to a 709 standard, you will notice that in that mode, the gray is displayed as 50% on the waveform and the white at 98-100%, just as you would expect.

The DSC "S-Log Chart" provides a valuable tool therefore, in learning how to use, gain confidence in, and properly expose your subject when using the Sony S-Log feature. As 10 bit recording becomes more ubiquitous in digital cinema cameras the use of log curves and raw recording will as well, and cinematographers will have to learn new tricks, and use new tools to set exposures that will result in pictures with extended dynamic range. Whatever the curve; S-Log, C-Log, RED Raw, etc. an easily read chart that targets the middle gray and the white chip will be invaluable. My thanks to David and DSC Labs for building such a tool.
 

DSC's TechTip
for May 2010 comes from

Dave Adams

Sky Television, UK

The Subject - "Selecting Production Parameters to Ensure that Picture Quality Accommodates the Intended and Possible Future Imaging Systems"

"Selecting Production Parameters to Ensure that Picture Quality Accommodates the Intended and Possible Future Imaging Systems"

Many people have written about using a CDM chart to obtain an optimised matrix for their camera. In a moment I will discuss the best technique that I believe enables you to do this, but let's first take a moment to think about why we might want to optimise our matrix. 

If a CDM chart is to be trusted then the colours it displays once viewed through a correctly white-balanced camera, should appear at certain pre-determined points on the vectorscope under ITU-709 recommendations. Not all cameras do this but the reason we might want to do this is with the aim of reproducing the scene as realistically as possible. As an engineer this should be your first starting point before building any custom look. 

First of all we must banish the use of any multi-matrix or colour corrector from the optimisation process as they are non-linear tools. The linear-matrix is what effects the RGB response curves. This technique has been designed to be repeatable in any controlled environment without the need for laboratory conditions – a dark room with a single black-body light source is ideal. 

Any CDM chart with at least 24 colours will enable you to optimise your matrix, although the more colours the better. The Harlequin chart is ideal for custom matrix building – with over 170 precision colours you can see with even greater detail as to how you are adjusting the colour-space. 

There are two important things to bear in mind: 1) Linearity is key; and 2) Throw away the vectorscope. Luminance cannot be viewed on a vectorscope but can be on a waveform monitor, along with hue and saturation. Instead, use the vectorscope at the end to check your results. 

Working with the colour-space as a whole is near-impossible. The best method is to divide the colour space into six sectors, each comprising of a primary colour, a secondary colour, and all in between [Figure 1]. You can now build six individually-optimised matrices; one for each sector.  

If each sector given above is in turn displayed at line rate, then the waveform monitor will show two horizontal lines when looking at the most saturated colours – in this instance one at 551 mV, the other at 289 mV – and a third which steps between the two. 

View the two linear [i.e. un-stepped] channels for any given sector in RGB overlay on a waveform monitor and the optimisation process can begin. One of the six axes of the linear-matrix will change the amplitude of one colour channel, and a second will linearise it. The third and fourth axes provide the same functions for the other linear channel. The fifth and sixth axes change the hue of the primary and secondary colours; however this can introduce coefficients that have a negative impact once the results are averaged so generally little adjustment is made. [Table 1].

 Averaging these results for all the sectors creates a 'first compromise' matrix.  The results from all six sectors are tabulated and shown in Table 2. [These values have been disguised and are not intended to be representative of any camera].

 Some of these coefficients are rather large. Large weightings are required to achieve the best results for individual sectors, but once averaged they distort the other sectors too much.

 A coefficient of ‘68’ is where abnormalities tend to start occurring on this example.  Trial and error proved that a capping value of ‘51’ gave the best results overall. Shown in Table 3 are the new results after the artificial cap has been applied.

 The coefficients in Table 3 now provide a compromise for the colour-space at large, but they are not necessarily the best for skin tones.  In this example, one final adjustment to B-G is made on their behalf to complete the optimization process. [Table 4].

To summarise the process, compare Figures 2-5 taking into account RGB linearity, signal-to-noise, vectorscope phase and ‘dot’ irregularity.
 

Figure 2 – HD Camera with no matrix adjustments	Figure 3 – Matrix adjusted using linearization technique
Figure 4– HD Camera with no matrix adjustments	Figure 5 – Matrix adjusted using linearization technique

Your camera will now reproduce the scene as realistically as possible and you are now in a good position to build your own custom look by modifying your results or this technique.

 This TechTip has been adapted from the paper Selecting Production Parameters to Ensure that Picture Quality Accommodates the Intended and Possible Future Imaging Systems which was presented at the SMPTE Tech Conference in Hollywood, CA, 27^th October 2009.
 

DSC's October TechTip
for October 2009 comes from

Tony Salgado
Digital Imaging Technician

The Subject - "Establishing a repeatable baseline reference"

The introduction of digital cinema cameras such as the Sony F23 and F35 series cameras which allow recording in various gamma modes such as S-LOG, Hyper Gamma, and user gamma modes can lead to potential post production confusion when photographing a gray scale chart on how to interpret the exposure values represented on the individual chips.

A CamAlign chart shooting technique which minimizes such misunderstandings can be accomplished by indicating on the chart the precise IRE or millivolt values which the peak white, middle gray and black chips represent for the specific camera gamma mode chosen to photograph a scene. The CamAlign chart can be photographed during the camera prep or in advance of principal photography, as it will be used to establish a unity baseline reference to aid in determining the post production grading LUT.

For example in S-LOG mode (loosely referred to as flat pass viewing) on a DSC CamAlign ChromaDuMonde chart, the white chip on upper left and lower right represents 65 IRE (reference the Green channel), 100 IRE when viewing the Sony ITU 709 180% dynamic range LUT and 90 IRE when viewing the Sony 709 800% dynamic range LUT. Indicating the precise IRE or millivolt values on the chart will become even more critical with the ability to create custom user in camera viewing LUTS which can be recalled on set. If any of these viewing LUTS are chosen by the DP and/or DIT for the initial grading of dailies etc. it will be critical to establish a firm visual “roadmap” with a CamAlign chart to insure a unity baseline reference throughout the course of the entire production.

In addition, it is highly recommend to write the HDCAM SR playback frequency frame rate, sampling rate and camera gamma mode information on the test chart, slate and tape labels to aid in avoiding any confusion later during post.

Example: 1080 23.98 psf 4:4:4 SQ S-LOG, 1080 23.98 psf 4:4:4 HQ S-LOG, 1080 29.97 psf 4:2:2 Hyper Gamma 7

It is always in the best interest of the DIT to protect the DP’s original creative intent by shooting a DSC CamAlign chart so that post production will not have to guess or question what the DP had in mind in terms of exposure. In the world of production, many items can be left open to interpretation, however the visual intent of the DP should not be one of these.

We are grateful to Tony Salgado for this month’s Tech-Tip on Establishing a repeatable baseline reference.
 

DSC's TechTip
for August 2009 comes from

Art Adams
Director of Photography

The Subject - Matching Multiple Cameras

"Matching Multiple Cameras"

This question was recently posted on the Cinematography Mailing List:

 "I need to match two Sony EX3 cameras to an HVX-200. How do I do it?"

My suggestion was to shoot a perfectly lit and exposed DSC chart on all three cameras, using the same criteria for setting exposure (placing the white chip on the chart on the same luminance value for all three cameras) in order to facilitate post color matching. A colorist should be able to match the cameras by looking at the star pattern the chart creates on a vectorscope and bending the points of each camera's star to match. It's important to match the cameras' gamma and knee settings in advance, as a colorist may have a more difficult time matching those. The DSC chart's gray chips form an "X" pattern on a waveform monitor, and the goal is to create matching "X" patterns on all three cameras. Match the most adjustable camera (the EX3) to the least adjustable camera (the HVX-200) by manipulating the gamma and knee settings. The knee circuit will interfere with the top part of the "X" pattern so it's probably best to shut that off and adjust it separately after gamma matching is complete.

If you have some time to spend in prep it might be possible to match camera colorimetry in advance using the EX3 user matrix. Using the less adjustable HVX-200 as a reference, adjust the user matrix for each EX3 so that the star pattern, created by the DSC chart on the vectorscope, matches that of the HVX-200. Always use a single waveform/vectorscope and monitor when matching cameras. No two monitors are the same, so looking at all three cameras through a single monitor eliminates that variable. Route the HVX-200 into the "A" input on the waveform/vectorscope and one of the EX3's into the "B" input, and then toggle between them while making adjustments. Once the first EX3 is matched to the HVX-200, repeat the process with the second. The Leader 5750 waveform/vectorscope is a great tool for this as it is simple to capture a still frame from one camera's star or "X" pattern and overlay a live image from the other camera on top of it. Then it's just a matter of adjusting the second camera's pattern so that it overlays the first.

One local rental house took this a step further and matched their EX3's colorimetry to a Varicam, as they considered the Varicam's colorimetry to be more pleasant.

We are grateful to Art Adams for this month’s Tech-Tip on Matching Multiple Cameras.

DSC's TechTip
for March 2009 comes from

C. R. Caillouet
Video Engineer - internationally recognized for technical innovation.

The Subject - Skin tone Waveform Levels

"Skin tone Waveform Levels"

There is nothing magic about 70% video on Caucasian skin tones.  The level depends on the impression that you are trying to achieve with the scene. For me as an engineer, the most important issues are to prevent the color components of skin tones from being clipped and to keep sufficient signal so that the faces are not lost in the mud, BUT, the overall mood of the scene might call for variations, depending on what "look" the Director of Photography wants.

Remember that a luma signal on a waveform monitor only represents the brightness component of the video and that is composed of approximately 60-70% green (depending on your color encoding standard), so to get a warm skin tone up to 70%, the red component may already be at or close to its limit. Pushing the exposure to get to a specific number can often lead to flattening of the red channel highlights, resulting in a "pasty" skin tone, especially if you are using aggressive knee controls.

A good comparison reference is the "CamBelles" chart, which comes in the CamBook series from DSC Labs. It contains several different skin tones in one image. http://www.dsclabs.com/cambook.htm
 

Recently there has been more interest and mail on skin detail than any other topic.  There are two reasons:

• HD with its increased resolution

• Aging TV personalities - the “Wrinklies”

Skin detail is a complex issue where lighting, makeup and camera adjustment all play important roles.  DSC can’t do much to help you with lighting and makeup, but we have developed a useful tool that helps set skin detail circuits objectively.  The idea behind the "DeWrinkler” test pattern is to provide more consistent results and, to save time, by eliminating the subjective component.  This is an early introduction to DeWrinkler which will be formally introduced at NAB next month.
 

DSC's TechTip
for December 2008 comes from

Walt Lindblom

Video Engineer with SAIC
NASA DTV Program

Video Engineer with SAIC
NASA DTV Program

The Subject - Compromise between Color Accuracy and Signal Noise

"Compromise between Color Accuracy and Signal Noise"

At NASA our objective is to capture the highest quality and most accurate images possible.  However, there can be a trade-off between color accuracy and overall image quality which impacts on how the cameras are aligned and the original image is captured.  These decisions are important because the images will live in the NASA archives forever.

When using the ChromaDuMonde CDM-28R chart, we have found that bringing all of the color chips to full saturation can cause problems.  Specifically, extending the response of the green and cyan chips up to full saturation can cause noise on some cameras.  While full saturation on all colors results in the most accurate color reproduction, it can introduce more noise than is acceptable for our purposes.  We have found that a reduction of about 20% in green and cyan saturation (moving the green and cyan signals 1/5 of the distance towards the center of the vectorscope) is a good compromise between color accuracy and signal noise.  We maintain the polygon shape DSC shows in their instructions.  This results in slightly reduced saturation in green and cyan, but it is still extended response in green and cyan when compared to the factory setting of any camera we have checked to date .  We feel that the slight reduction in green and cyan response is beneficial overall as it still provides very accurate color reproduction and produces less image noise, which is exceedingly difficult to remove later.

DSC's TechTip
for November 2008 comes from

Dan Mulligan, DP - UK

The Subject - Do You Waveform Monitor the Lutted Image or the S-Log?

"Do You Waveform Monitor the Lutted Image or the S-Log?"

I waveform the S-Log, the LUTs on set can wack out the waveform (imagine waveforming the Rec 709 output, ouch!) and they really are, for most reasonable purposes, for comfort viewing only. You can go very deep into LUTs and start some very sophisticated looks, using the waveform to really balance your RGB values, but that needs careful and thoughtful application and a good working relationship with your post team, but you really can achieve some lovely results.

The S-Log is my neg and that’s what I want to waveform and look for black level and clipping. Once exposed, then toggle to your desired LUT for that scene/shot.
 
For most log images on set, which are mostly partially colour temperature corrected in camera, then a simple bit of contrast to the blacks will tighten up the image enough for a pleasant on-set look and the waveform will confirm your stop value/black level loss with your desired LUT applied, but for me its the S-Log/Neg I'm interested in first - LUTs come next.

Mike Richardson
holding a ChromaDuMonde for Dan

You can always tell which professionals use their CDMs all the time . . .

. . . they're covered with gaffer tape

DSC's TechTip
for June 2008 comes from

George Walkley

The Subject - Matching the Sony EX-1 with more costly Broadcast Cameras

"Matching the Sony EX-1 with more costly Broadcast Camera's"

We have been creating custom profiles recently for our customers who have purchased XDCAM, HDCAM, and Sony’s new PMW-EX1 and other cameras.  We need to match them all for particular clients for particular shooting environments.   It is absolutely necessary when creating profiles to have the correct aides to guide you and to have the end user with you (important) so that he/she is comfortable with the final look you create.
 
All of the menus are just numbers that you adjust for the response you want.  Unless you have a calibrated monitor, calibrated chart that is correctly lit and so forth, you can tweak all you want and not come up with the result you would like.  As a tech I understand this, but rather than confirming that factory specs are giving a correct response, I dive into having fun creating picture profiles or scene profiles with the customer, while keeping away from undesirable responses. 
 
One thing that is a must with HD is avoiding washed out high-lights that get blown out as soon as the scene is saturated with light.  All the cameras listed above plus some others really need some help as they come out of the box.  DSC Labs’ charts help with developing chroma profiles, black stretch adjustments, flare adjustments, etc, with confidence.  Because the EX1 is loaded with things to tweak, including an individual color with phase and saturation ability, the ChromaDuMonde chart really helps me confirm that I’m getting the result I want without getting unsatisfactory results in other areas of the setup.
 
I have gotten tons of compliments from our clients that shoot major outdoor and other types of projects with a variety of cameras on the same shoot.  The cameras will all have the same profile characteristics - PMW-EX1, PDW-355’s, and HDW-730’s for example.  What’s amazing is the Sony EX1 and just how great it looks, especially for the money.  I’m not trying to sell an EX1 but I have to admit the blacks look awesome, the chroma is fabulous and the grey scale is superb.
 
These new cameras allow you to tweak your ‘---‘ off, but you need a guide to do it properly!  A good chart is a must.

DSC's TechTip
for April 2008 comes from

David Blackham

The Subject - Continuous Light Sources

"Continuous Light Sources"

There is a growing trend to use fluorescent, LED and discharge light sources for film and video production.  This is good news for the environment as these light sources use less power than conventional studio lights.  As the power consumption is less, so less heat is generated on set.   Environmental issues should not be ignored when considering technical and creative requirements for production - being environmentally responsible has practical benefits too!

One of the problems faced by these light sources is the lack of continuous spectrum activity, exemplified in fluorescents, LED and other discharge fixtures. It is impossible to add light that was not present in the first place but spikes can be removed with suitable gels (e.g. minus green for green spikes). Often, light sources originally designed for film and television are used with video – this is common on productions with lower budgets, and may be why there are so many brands of CFL bulbs.  If selected with care, many of the quality bulbs have a high CRI and are useful sources of light. Video and digital cameras have a greater tolerance to low CRI light sources and they can be easily balanced during image capture, but only when a neutral DSC test pattern is as a reference.  CRI figures are not a guarantee that the source has a continuous spectrum, but can be helpful when selecting potential light sources.  Much of this information can be found on the internet.

When using new fluorescent tubes from any manufacturer, a common practice is to burn the tube in for at least 24 hours before use.  This allows the tube to stabilize and become consistent in its output.  Try and use light sources with a high CRI and suitable CCT when budgets allow. Occasionally, light sources that deviate from 3200k or 5600k are welcome on set, so long as the quality of light from the source remains constant in terms of CCT and spectrum. A meter is not always necessary to determine colour temperature as many Digital cameras have onboard indicators.

A guide to monitoring continuous spectrums of light is easy with DSC Laboratories test patterns. The front lit ChromaDuMonde 28R is a necessity to identify light sources that may not have a continuous spectrum. If the camera is calibrated with a continuous source (such as tungsten lamp) then a similar colour temperature fluorescent source can be compared on a vectorscope display. This may not be standard practice, but this technique is useful as it requires basic tools found on common sets.  Monitor calibration is of equal importance - especially when shooting on location.  I use a Spyder 3 monitor calibration device made by Datacolor. Location viewing environments may not be the perfect calibration spot, but the device is simple and, when paired with a DSC Pattern, easy to use when trying to achieve perfectly neutral imagery.

DSC's TechTip
for March 2008 comes from

D. Gregor Hagey CSC

The Subject - Red One and CMOS Static

Learn more about Gregor here

"Red One and CMOS Static"

Every time you change a lens on a digital camera such as the Red One, be sure to check the sensor for dust. The single CMOS sensor has a static charge that attracts dust (just like DSLRs). Use a loop to magnify the sensor before blowing gently with a blower bulb or compressed air.  If blowing won't remove the dust, then use a brush designed to clean DSLR sensors, but use it with great care. 

When dust is left on the sensor it appears as a soft grey blob in the image. This is not always visible on small displays and might not be noticed unless you see your work on a large display or projector.

DSC's TechTip
for December 2007 is from

Reid Robertson
Reid is a Digital Camcorder Specialist with Panasonic Canada.

The Subject - Back Focus

Always remember when performing a "flange-back" adjustment (as Back Focus is sometimes called) the Iris should be FULLY OPEN. When the Iris is wide open, the depth of field is minimized, giving you the optimum focus point during your adjustment.

When there is too much light, use the ND filters in the filter wheel to cut it down to a useable level. If there are no ND filters available, use the "Poor Man's ND": higher Shutter speeds (this trick comes from the CCTV world). I cheat and also use the Viewfinder Peaking set to maximum, to find the best focus during the adjustment.
Rebuttals on Back Focus:
Just received your tech tips #9. With all respect, the suggestion to use max vf peaking, is suspect, in the same sense that doing a back focus at f/16 would be wrong. The idea is to make it more difficult, and more critical, than less so. My recommendation is always minimum (or just the least bit) of viewfinder peaking. - A. L. New York
**********
Hello DSC, a comment from someone who used to work for a HD colour viewfinder manufacturer - on Sony 730/750/900 we used to find that setting the VF peaking at about +70 (It goes from -99 to +99, with 0 being the default) gives a much better image on which to judge focus. Note, setting this peaking does NOT affect the image recorded to tape, it purely lifts the transitional edges slightly in the VF so that they "Snap In" at the point of critical focus. - RB London UK
**********
I guess by "difficult" the commenter means "difficult to be satisfied with what you see" rather than "difficult to obtain the desired result"?

Let us define "difficult" in the most common connotation of "difficult to do." Then, less sensitive = MORE difficult to see and do. More difficult = LESS sensitive! You want it more sensitive, yes! But less difficult to see the right adjustment. That's why you don't use f/16, which makes it LESS sensitive and MORE difficult. Max peaking, on the other hand, lets you see a slight decrease in sharpness as you move away from the optimum point. MORE sensitive and LESS difficult. - WB Illinois
**********
Here's the correct way to do it, real easy.
Open up the iris completely, and get your camera to deal with the light. Use any means available such as shutter and filter wheel to get the camera to deal with the lens wide open. Next zoom in completely and focus on your subject. Then zoom out completely and adjust back focus. Repeat a couple of times since these adjustments interact slightly.
This is the best way to do it, because this provides you with an individual back focus setting for your specific shot. Not a problem normally except if you have a really good lens coupled with a very good camera. Normally, you should just do this for a shot at infinity, and leave the lens set up this way for the next person using it.
Viewfinder peaking helps find the "sweet spot", always maximize it if you need to. Main problem with Back Focus is that people don't get that the Iris has to be WIDE open doing this.
Reason is simple. Before lenses we had pinhole cameras. They were really cool. A box with a pinhole in it and a piece of film on the other side. No problem with any focusing of the lens whatsoever, and always a great shot. Might take half an hour to get a good shot without anyone moving their face. Probably why old photos show grumpy looking people. - JK CA
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As far as I can tell, the cameramen I work with, who've also been doing this for 25+ years, do just the opposite of what this fellow above suggests.

They crank the living daylights out of their viewfinder peaking. Their objective is to make the image jump off the eyepiece and into their eyeballs when they've hit critical focus.

I do the same thing when I'm adjusting back focus, or doing other focus critical alignments.
LC - NY
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Setting VF peaking to max for back focus alignment, was also very suspect to me. Depending on the condition of VF and camera, it's someVerdanaecessary to use a certain amount of peaking in order to get the best result, but only in the very wide position of the zoom.
That's how I do it sometimes, but as soon I zoom to the tele position, to adjust the focus, I turn down the peaking. That's more work to do (especially when repeating the procedure many times...), but it pays.
I think, the max VF peaking might only be suitable for an "emergency setting" in the field, when no Siemens star is available and whatever is in front of the lens has to work as a test chart. Best regards from Switzerland - MR
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Gee, if we are going to turn the viewfinder peaking down, I guess we should go back inside the camera and turn off the enhancement contours like my engineer friends did back in the Norelco PC-70 days! That would help even more to make it nearly impossible to get meaningful results under field conditions.

Viewfinder peaking is on a display, therefore it enhances what you CAN see. If you would look at a waveform monitor you would see the same thing that peaking shows on the viewfinder - a very stark "snap" in and out of focus. Peaking (and the waveform monitor) is also helpful in cases where you are too far from the chart and it is too hard to see detail at the wide angle setting. How far should we be from that chart, anyhow? And repeat the process at least twice. DG Iowa

DSC's TechTip
for September 2007 comes from

Greg Foad

The Subject - Are Six Colors Enough

Learn more about Greg here

Image A

Image B

"Are Six Colors Enough?"

Believe it or not, the camera that shot this 28 color (Image A) ChromaDuMonde was accurately aligned to a six color (Image B) CamAlign chart (note - the six primary colors are still in their boxes).  With the advanced handles on many HD cameras, matrix alignment can be misleading.  

The testing lab at DSC reminded me of a crash test dummy plant.  Various test charts and wacky designs lay everywhere - some had been yellowed from radiation exposure, others bent in testing shipping packaging, and others were just designs that never made it past the testing stage.  I was there to help DSC capture image scenes onto a WFM7100 USB buffer for an application note they were writing for Tektronix.  We used my Sony F900 to test color reproduction using different test patterns.

What we came across was quite astounding.  We first used a standard CamAlign six color pattern with crossed grayscales.  With only six colors to work with, the multi matrix controls on the F900 allowed me to put each color in its box very quickly - camera alignment took no more than 10 minutes… or so we thought.  The green and cyan dots seemed to have an oblong shape, so I was skeptical that we had aligned them correctly.  Sure enough after putting up a 28 color ChromaDuMonde, we saw the vastly misshapen hexagon.  One goal of camera alignment is to adjust its taking characteristics to accurately reproduce the widest possible range of colors – not so in the first image.  Clearly, we would be better off using one of the factory presets then using this skewed matrix.

While both user and multi matrix settings appear in the paint menu of the camera, they have very different functions.  The user matrix was originally intended to help warm or cool an image, depending on the shot.  The algorithms behind this circuitry grab clusters of colors and pull them fore and aft, i.e. R-B, B-Y, etc.  The multi matrix controls uniquely allow selective color enhancement and hue adjustments up to 20 degrees.  These controls are powerful, as they only select one color independent of any intermediaries.  So, the correct alignment sequence is to adjust the user matrix first, and then use the multi matrix controls for fine tuning.

So, this tech tip begs the question – are six colors enough?

DSC's TechTip
for June 2007 comes from

Bruce Alan Greene
Originally appearing on the CML site it is reprinted with kind permission from Bruce and the CML

The Subject - Varicam Detail

Learn more about Bruce here

"Varicam Detail"

On my last major Varicam project I conducted a film out test and included a variety of detail settings in the test.  After viewing the film print on the big screen I selected a level of detail that I believed added enough "punch" to the image without any noticeable detail artifacts visible in the print. In the test I was surprised by how much added detail the film print would tolerate, though to be fair, I've developed a subtle eye for "Sharpening" through years of Photoshop work.

For the Varicam, I decided that "Master Detail" could be set as high as "0" before I didn't like the look. To be on the safe side, I shot with master detail set to minus 2. At the factory defaults for all the detail parameters on the Varicam, master detail = -7 is the same as "detail off". Master detail set to "0" is a significant amount of detail on the Varicam.  For the most part I ended up happy with my detail setting until...I had a shot of a woman against a bright blue sky. On my 17in LCD monitor, I could just start to see an outline where the woman met the sky. I then dialed down my setting a couple notches. 

My advice for anyone brave enough to turn on the detail is to view your test image and test charts on a large LCD monitor that has a true pixel to pixel representation of the image. I think if one judges by CRT then one is apt to add too much.  Also, it is very important to use a waveform monitor when adjusting the detail. You will see changes in the detail settings on the waveform that you will miss by looking only at a monitor. 

I hope this is of some help to those interested in this discussion.

Bruce Alan Greene
Los Angeles

DSC's TechTip
for April 2007 comes from our

User Database Reports
This is a compilation of similar ideas from a number of different users.

The Subject - Noise, Green, Cyan, and Saturation

"Noise, Green, Cyan, and Saturation"

When data acquisition for scientific applications is the main purpose of image capture, precise camera setup is of even greater importance.  For that reason, we are used to hearing very specific guidelines from clients that the norm does not always follow – for instance, some of our clients capture only in a progressive field mode, as testing has shown interlaced to be less reliable (an arguable, but tested opinion!).  Another pertinent example includes lining up a DSC Labs ChromaDuMonde with 80% Green and Cyan saturation, as opposed to lining them up directly in their vectorscope boxes.  Some clients align the phase of the green and cyan chips to be in plane with their appropriate vector boxes; however when boosting the saturation values, they do not max that setting out on the camera just to get the greens and cyan's square within their boxes.  As many cameras come from the factory with greatly warmed G’s and Cy’s, clients have found themselves maxing out our saturation values in order to get the colors deadset in their boxes and this can create a fair amount of noise in the darker areas of the image - this will vary from camera to camera.  Operating with a buffer is a good engineering tip. 

One client recently described the process as follows - 'For simplicity's sake, let’s use a Varicam to quantify this process.  Take a DSC Labs ChromaDuMonde 28 color pattern, and using the Color Matrix and Color Correction settings, align Y, R, Mg and B up, whilst aiming the G and Cy chips at their targets.  Then, we increase the saturation of these chips within the color corrector until we are at about 20% of where they should be.  As the Y, R, Mg and B chips are already near their boxes, setting these colors is relatively easy.  The G and Cy chips however, are much farther from their targets, and therefore require a significant boost in gain, even though we do all of our set ups with a zero gain setting. When all of the colors are lined up, the end result is a bit noisy, as if we were lining up with an increase in gain.  The same increase in dynamic range as used in the ‘gain’ setting must be applied to the saturation settings within the camera’s color correction controls.  This process may be considered subjective, and we are not preaching it as gospel, however it produces a satisfactory colorspace with a limited amount of noise, which works perfectly for us.'

DSC's TechTip
for February 2007 is from

David Mullen, ASC
Originally appearing on the CML site it is reprinted with kind permission from David and the CML.

The Subject - Tips on HD

Learn more about David here

"Tips on HD"

When shooting digitally and recording to a fairly compressed format like HDCAM / DVCPRO-HD, I sort of subscribe to the "fifty-fifty" thinking (although the true breakdown may lean more towards in-camera than post) by which I mean "get close to the look you want in terms of the original photography / recording and finish the look in post." You don't have to get 100% of the look in-camera if it is more efficient, especially time-wise on the set, to complete the look in post. On the other hand, the compression of HDCAM, for example, limits how far you can push an image in post before you start to pick-up artifacts, and some types of image manipulation are more artifacty than others.

For example, adding more contrast, which may involve crushing the shadows and/or clipping the highlights, is probably best saved for post, whereas lowering contrast, increasing shadow or highlight detail, should be done in-camera with proper lighting / exposure.

If you are unclear as to how to manipulate the Color Matrix, then yes, I would get a DIT involved. As far as doing a silver retention process to the final prints, there will be some desaturation and increase in contrast in the shadows, with deeper blacks, so keep that in mind when shooting and when doing the final color-correcting. I recommend doing a test before you finalize any color-correction decisions. Luckily if you choose Technicolor's ENR or Deluxe's ACE print process, you have a lot of flexibility in controlling the degree of silver retained, although on a reel-by-reel basis, not shot-by-shot.

DSC's TechTip
for June 2006 is from

Robert Goodman
Emmy-nominated director and  the author of the "Goodman's Guide" series of field guides for SD and HD cameras

The Subject - Creating a Look

Learn more about Robert here

"Creating a Look"

Creating special looks for any camera starts with a baseline. I establish that baseline using a ChromaDuMonde chart.  Once you set the camera up to what is essentially normalized technical accurate reproduction, you can begin to deviate from that norm.

Manufacturers generally set up the camera at the factory to reproduce pleasing skin tones by altering the color gamut of the camera. This is no different than Eastman Kodak color balancing Kodachrome so it reproduced bluer skies and reds more brilliantly than were often present in the actual scene.  Fujichrome made greens look more lush and skin tones creamier than reality.  And you can do the same with most of today's digital cameras.

Under DAYLIGHT BALANCED lighting, shoot a ChromaDuMonde chart and use the camera's controls to reproduce it on a Vectorscope so all the main targets are in their boxes.  You'll need to increase the gain to approximately 1.875 (for charts after May 2007 use X2 vectorscope gain) instead of the CAL (calibrated) setting because of saturation.  Make sure you have a evaluation grade monitor preferably a CRT or one of the carefully calibrated LCD monitors, which are costly though less costly than the evaluation grade HD CRTs.

With the proper tools, you can begin to create your own looks.  Want a warmer, more pleasing look than the "technically accurate" look you just created?  Adjust the camera's controls to skew the color reproduction of the blues and cyans towards the reds and yellows.  Want a cooler look? Skew the color reproduction of magentas, reds, and yellows towards blue and cyan.  It will take a lot of trial and error to get what you want.

Pay careful attention to the impact of changes on the intermediate colors.  Try to keep the spacing between intermediate colors on the vectorscope uniform.  Remember that when you skew the color reproduction, you are eliminating colors so don't go too far overboard if you want to reproduce a nearly full color gamut.

Have fun and let yourself go overboard.  In making adjustments you'll discover the limits of the camera and perhaps a stunning look.  Every shot doesn't need to reproduce color accurately.  A cinematographer's job is to depict emotional truths.   Accuracy is for scientists.

A few final words: Style is over-emphasized; if the audience is watching what the cinematographer is doing they aren't involved in the story.  Subtle color changes resonate and alter the mood of audiences in ways that heavily filtered images never can.

Robert Goodman has conducted workshops on digital production and post for AIVF, Guild of Professional Photographers, IFP, ITVA, SMPTE, Sony Corporation, Women in Film, and at film festivals in Atlanta, Austin, Los Angeles, Minneapolis, New York, Philadelphia, Portland, San Diego, and San Francisco.

Mike Brennan
Mike is a leading DP in London, England and editor of High Definition Magazine.

The Subject - Aberration Issues

"Aberration"

For a few years I've assumed that it could be worth spending many dollars on high quality HD zooms to improve the performance of wide shots that all seem a little soft on HD.  In the past few years I'd noticed lateral chromatic aberration on standard quality HD zoom lenses (colour fringes either side of verticals), mostly on wide shots and assumed a high quality $70k HD lens would reduce the colour fringes.

What has been annoying is that all the frame grabs I had ever seen of my DSC charts in my studio look pretty good, as do everyone else's frame grabs, but location wide shot frame grabs still suffer the lateral aberration.

First, lens manufactures have a hard time focusing Red Green and Blue light to an equal distance through the optical block. In fact they get a helping hand from the camera manufacturers who created a standard where the red green and blue CCDs are not set at equal distances on the optical block; this has enabled TV lenses to be designed with 40x or 100x zoom ratios and film lenses (where all wave lengths have to be focused on the same plane), become virtually impossible to make past 25x.

However, it is still a devilish task to create a zoom that is perfect at all focal lengths, impossible in fact, but each zoom lens does have what DPs call a sweet spot.  This is a focal length where RGB rays are as good as they can get.  There is a residual lateral aberration in the form of an inherent problem in the prism - (well, camera manufacturers pass the responsibility to the lens manufacturers and lens manufacturers blame the prism itself!)

The problem becomes increasingly evident below 12mm and is really quite a problem at 5mm or 6mm.  Having tested many lenses on many cameras, it is evident on all lenses and cameras. 

This sweet spot varies with each lens.  A sweet spot on a Canon 40x lens, for instance, is 100mm whereas a 21x may be 14mm.  Both focal lengths aren't too long or too wide so that a test chart can't be shot in a lab without knocking down a wall.

So most of the charts I shoot, say testing gamma curves, are usually well above the focal length where the aberration is a problem and also are in the sweet spot of the lens!  So I have a brilliant collection of frame grabs with the DSC chart neatly filling the frame where there is near zero aberration, and a collection of wide shot frame grabs with problems.

So why hasn't this aberration been noticed on our test charts?  It is only recently we have pixel perfect registration in LCD monitors and, combined with 1920x1080 10 bit recording rather than 1440x1080 pixel 8 bit recordings, we are seeing more fine detail.

The main reason is that we rarely shoot a test chart on a wide lens where it fills the frame.

Pretty basic!

Since there are no 10 foot wide charts my tech tip for testing the wide end of zoom lenses is to shoot the DSC chart on the left and right edge of frame at 4 meters.

If you have a technical suggestion to share - please send it to "TechTips" <dsc@dsclabs.com> for consideration in a future "DSC TechTips".

Charlie Goldman
Charlie Goldman is a leading video engineer on popular shows such as Canadian Idol, Cirque du Soleil, etc.

 The Subject - Color Bar Symmetry

"Color Bar Symmetry"

Producing consistent accurate color reproduction can be a challenge, particularly under different lighting conditions.  Whether I am shooting the Olympics, Rock concerts, or Ice hockey I use the same basic technique.

It is helpful to understand the engineering behind DSC colorbars.  All DSC color chips are mid saturation and represent real life colors.  Each color is designed to produce levels of 80 and 40 IRE analog or 560 and 280 mV digital.  An increase in vectorscope gain of 1.875 will put all the signals in their boxes when a camera is aligned for accurate reproduction.

In analog systems, this simply means increasing vectorscope gain to position the burst opposite the outer corner of the yellow box, then adjust the matrix to set CamAlign's RGB and CMY color chips in their boxes.  A number of scope makers now incorporate the 1.875 factor for DSC charts in their new digital scopes or provide a calibrated readout of gain level.

Older digital scopes do not have a calibrated gain function, so in these situations I adjust the matrix to produce Red chip waveform levels of Red 560mV,  Green 280mV and Blue 280mV.  I then match the other colors to the same saturation on their appropriate vectors.  Be more concerned with the lower values than the higher, because errors at the 280mV levels will have a much larger visual effect than variations in the 560 mV level.  Dave gave me this tip years ago, told to him by a Sony engineer in Chicago.

Charlie Goldman will be featured in an upcoming "Spotlight" at http://www.dsclabs.com/

- If you have a technical suggestion to share - send it to "TechTips" <dsc@dsclabs.com> for consideration in a future "DSC TechTips"