January 05, 2014

Luma and Waveforms

January 05, 2014/ Bennett Cain

Luma and Waveforms

It’s late. I’m jetlagged, sleepless, and sitting in a hotel room. There's nothing on TV but I’ve got a Sony EX3, a Leaderscope, and a 11 step grayscale chart. Let’s talk about video luminance, or “Luma” as it’s more correctly known.

I'm sure there's a more elaborate definition out there but this one from Wikipedia sums it up nicely.

“Luma represents the brightness of an image (the “black and white” or achromatic portion of the image). Gamma-Compressed Luma is paired with Chroma to create a video image. Luma represents the achromatic image without any color, while the chroma components represent the color information. Converting R'G'B' sources (i.e. the output of a 3CCD camera) into luma and chroma allows for chroma subsampling, enabling video systems to optimize their performance for the human visual system. Since human vision is more sensitive to luminance detail ("black and white", see Rods vs. Cones) than color detail, video systems can optimize bandwidth for luminance over color."

Luma is measured on a waveform monitor by either a millivolt (mV) or IRE (%) scale. IRE is intuitive because it represents the percentage of light to dark and for HD Video that scale is from 0-109. 0% brightness, 0 IRE, is black. 100% brightness, 100 IRE, is white. 109 IRE is super white (basically some head room for your highlights). Makes sense to me.

Luma together with Chroma make up the HD video image and for engineering purposes both can be manipulated individually with the correct menu settings. Color is controlled by the camera's LINEAR MATRIX, COLOR CORRECTION, RGB GAIN (white balance), RGB PEDESTAL (black balance) settings whereas Luma/Brightness is controlled with GLOBAL GAIN, PEDESTAL, GAMMA, BLACK GAMMA, and KNEE. Some cameras have slightly different nomenclature or menu features but these are the basic and universal controls for manipulating video Luma. Use these Luma Control tools to affect the image's Tonal Response or how Shadow, Mid Tone, and Highlight information is rendered.

In my opinion, creating beautiful HD images starts with good lighting. These engineering tools aren’t going to make a poorly exposed and poorly lit image good but they can help make a good image great. Remember that for an 8 bit camera you’re trying to cram all the scene’s brightness information into 256 levels of gray. That’s not much to work with and if you’re dealing with extreme contrast, the menu can help but there are limits to what's practical.

The Variables:

MASTER PEDESTAL most noticeably affects the bottom of the waveform or the black/dark/shadow portion of the signal. If you think about your waveform as if it’s an actual pedestal or column you’ll see that by increasing or decreasing the Pedestal value, you’re actually lifting or lowering the entire signal. The picture portion of the video signal can’t go below 0 IRE so by lowering the Pedestal or “crushing the blacks” as it’s often referred to, what you’re actually doing is compressing the dark picture information down to pure black, 0 IRE. Some cameras have individual RGB Pedestal controls as well which can be used to affect chrominance in shadows.

GAMMA as a television engineering topic is a complex one. But an interesting one! Gamma as it applies to camera menu settings primarily affects the Mid-Tones by starting at the middle of the waveform scale and either lifting or lowering the information there, which by default can subtly affect the shadows and highlights as well. In addition to a controllable Gamma level, most video cameras have several preset Gamma options such as HIGH, LOW, HD, SD, CINE, etc. Some but not all of these pre-made Gamma curves actually are a combination of various Knee, Pedestal, and Gamma settings designed to create a specific effect such as wide dynamic range, crushed blacks and popping whites, an overall lifted look, etc. At the end of this article, I’ll provide an example of this.

BLACK GAMMA is for Gamma fine-tuning and controls the area in-between middle gray and black, about 10-40 IRE. Black Gamma is a great way to punch up the blacks without crushing them or to lighten the fill side of a scene.

KNEE is electronic highlight protection and controls the top of the waveform or the bright/white/highlight portion of the signal. Video cameras have traditionally struggled with highlights and clipping so Knee circuitry was designed to help overcome this inherent problem. Where you set your knee point or in other words, where you tell the camera to begin compressing the white portion of the signal will greatly affect the quality of your highlights. Knee is not a power window in a color correction suite though. Knee needs some IRE to work with and if you’ve already exceeded the limits of the sensor’s bit bucket, adjusting the camera’s knee circuitry is going to have little effect. The Knee features in a camera's Paint menu often has a lot of controls other than just where the compression begins - you can also inject or remove detail as well hue and saturation into highlights, etc.

GLOBAL GAIN is an important part of the equation but gain is an overall video level that either boosts or reduces the entire signal which affects both Chroma and Luma. It's important to draw the distinction between global gain and RGB gain which is how camera white balance is controlled.

If you haven't seen them yet, please watch Andy Shipsides’ ENG Essentials on Abel Cinetech's Blog. His video on Gamma Matching is a great resource and is closely related to the information found in this tutorial. That video is more of a how-to on the subject whereas this is intended to illustrate how the camera menu settings specifically affect the grayscale and its accompanying waveform.

For the purposes of this test, I started by zeroing out all of the Picture Profile settings on the Sony, turned the knee off, and used the Gamma Mode of STD1 to set up a basic image to set up the comparison. The Leader's waveform mode was set to Composite instead of Parade (individual RGB waveforms) to better show the signal in terms of luma only. The lens iris was set to a F2.8/4 split and not adjusted for each of the various menu settings so as to illustrate how to affect the image in the camera instead of introducing or taking away light.

I want to see how the menu settings affect the entire picture from 0-109 IRE (note from 2014, should have been 0-100 IRE!) so first I need to make white, white and black, black. Initially with my lens at a F2.8/4 split, white just hit 109 IRE but the true black (the black rectangle in between the two grayscales) needed some help so I brought my Master Pedestal setting down to -14, setting it at 0 IRE. With this combination of Iris and Pedestal settings, the middle of the scale crosses at around 60 IRE and we have picture information from 0-109 IRE.

Here is our basic waveform that has picture information from 0-109 IRE. This will be the basis of comparison for the other menu setups.

And the accompanying properly exposed Grayscale image:

What's most important to know when using these tools to affect the image's tonality, is how to identify shadows, midtones, and highlights on a waveform monitor.

Let's have a look at what happens when we start altering our shadows by setting the the Pedestal. If you’ve been following this blog, you’ll know my thoughts on the mistake of arbitrarily crushing black. Here’s why:

PEDESTAL -50

As you can see, the information that would have been residing from 0-20 % has been crushed down to 0 IRE, or in other words, 0% picture information. No amount of post production wizardry is going to get that information back without introducing lots and lots of noise. So if you like crushed blacks, make sure you like them enough to live with them. Some shots can definitely benefit from stong, inky blacks but just be aware of what you’re doing.

Here’s what happens when we lift the Master Pedestal.

PEDESTAL +50

As I mentioned, Pedestal will raise or lower the entire video signal. While lowering it is a way to introduce contrast, raising it will take it away. Because lowering it crushes dark picture information down to black, it may seem like raising it would crush bright picture information into white. That’s not the case. As the Pedestal is raised the signal is compressed and black gets lighter and white gets grayer. Some DP’s will shoot with the Ped always a little lifted just so they can hang on to as much shadow and highlight detail as possible. This is great if you know there's going to be a DI or some grading done later. If this isn’t the case, you’ve really got to get it right in the camera and the flat look of lifted pedestal isn't the most attractive.

With the Gamma setting, we have some control over our mid tones. These controls are pretty subtle but can be a great way to quickly punch up or reduce the contrast without touching the blacks. This is more of a personal preference but I routinely drop the gamma a little bit to get bolder, richer picture.

GAMMA +99

GAMMA -99

As I mentioned above, Black Gamma is a great tool for subtly fine-tuning the dark portion of the signal and can punch up the blacks without crushing them.

BLACK GAMMA +99

BLACK GAMMA -99

And now we can affect the top portion of the signal, or White, by altering our Knee Point. Knee is a little deceptive because what it does is tell the camera where in the signal to start clamping down the highlight information. For example by lowering the number to 80, you tell the camera to start compressing the picture information from 80 IRE on. It works within the limits of the sensor though and information that is very bright and exceeds its limits of won't be noticeably affected. By turning the Knee off, you are not doing anything electronically to protect your highlights. As I mentioned above, Knee needs some IRE to work with and if you’ve already exceeded the limits of the sensor’s bit bucket, adjusting the camera’s Knee circuitry is going to have little or no effect. Some cameras have a White Clip setting as well which will not record any part of the signal past the value you specify. The Sony EX1 does not have a White Clip setting.

Here is the KNEE set to 100 which starts the compression at 100 IRE. As you can see, the highlights start to roll off at that point on the scale.

Here is the KNEE set to 75

And the lowest value on the EX1, KNEE 50

Highlight rendering can be further subtly fine tuned with the Knee Slope control which controls the shape of the Knee curve. This affects how quickly the highlights are rolled off to pure white. Very subtle!

KNEE 100, KNEE SLOPE +99

KNEE 100, KNEE SLOPE -99

CAMERA MATCHING:

We can use these tools to match the gamma curves of different cameras to one another. Also, your camera's pre-made Gamma options - STD, CINE, etc - are really a combination of various Luma control settings. With skillful use of these tools, you can actually recreate any of these effects pretty closely or even design your own custom gamma curve.

In this example, I set the camera to CINE 2, the most aggressive of the pre-made gamma options on the EX1. I left the lens to a F2.8/4 and captured the waveform. You'll notice because this curve clamps the signal down so much, it's quite a bit darker than STD1.

Here it is:

Next I zeroed out the settings out and reset the camera to Gamma STD1. Because CINE2 uses such aggressive compression, I had to close down half a stop on STD 1 to bring it within range. Using the menu, I adjusted the following settings to arrive at a fairly close match to CINE2, not perfect but pretty close.

PEDESTAL -11

BLACK GAMMA +12

KNEE 59

KNEE SLOPE -37

GAMMA -99

Here are the two curves superimposed over one another. Pretty close. With a little play in the iris, these pictures would be fairly well matched.

And for kicks, to better illustrate how aggressive these pre-made gamma curves can be, here are the Cine curves from the Sony XDCAM-EX camcorder series (Iris is the same for each curve):

Cine 1

Cine 2

Cine 3

Cine 4

Please support this blog by leaving comments and feedback. It's only through user support and feedback that this content can be fine tuned so I always appreciate hearing from you.

January 05, 2014

Painting HD Cameras - Skin Tones

January 05, 2014/ Bennett Cain

Painting HD Cameras - Skin Tones

In my experience color correcting video cameras in the field, 9 times out of 10 I’m trying to resolve some sort of skin tone issue – taking green out, bringing overly magenta skin back within a normal range, or sometimes just injecting a little bit of warmth and saturation. Knowing how to correctly use a video camera’s User Matrix menu and Color Correction menu as well as the Tonal Control menu is the key to working through these inevitable problems. In building upon my previous article on in-camera color correction for HDTV, this next article will specifically address how to use the various matrix menu attributes to affect skin tones.

This article builds off what was established in Painting HD Cameras - Basic Colorimetry.

Technical Notes:

The images used in this article were created with a Panasonic HDX900 and the stills and vectorscope information were captured from a Leader LV 5330 Multi-SDI Monitor. Because a Panasonic camera was used, the workflow presented and menu features explained are those found on Panasonic cameras. The feature set on Sony cameras is similar enough though that I feel that if you know one system, you should be able to apply the same concepts to the other. The chip chart used was a DSC Labs CamBelles Chart. These charts are the standard for video engineering and camera alignment. Because the colors and values are so uniformly printed and tested, they can be measured electronically with repeatable results. Correct use of DSC Labs equipment can not only be used to calibrate and match equipment but to paint custom looks in the controlled environment of your studio.

On naming conventions:

In most Panasonic cameras, the Linear Matrix is referred to as User Matrix and the Multi Matrix is referred to as Color Correction. In Sony cameras, Linear Matrix is referred to as Matrix Linear and the Multi Matrix is referred to Matrix (Multi). As this is a Panasonic oriented article, from here on out I'll be using the Panasonic nomenclature.

Part 1: Overview

First to re-hash, there are six attributes that affect a video camera’s Linear Matrix: B-G, B-R, G-B, G-R, R-B, R-G. Those are read “Blue into Green, Blue into Red, etc.” Additionally, there are twelve Color Correction attributes we can modify: R, Mg, B, Cy, G, Yl, Yl-R, R-Mg, Mg-B, B-Cy, Cy-G, and G-Yl. For an in depth account of how these attributes work by pushing and pulling colors around the vectorscope, please refer to the previous tutorial. Using the handy DSC Labs Chroma Du Monde Chart with its 4 "generic skin tone" swatches, let's have a look at our camera's "out of the box", default colorimetry:

Interestingly enough, virtually all human skin regardless of its hue or saturation resides somewhere within or nearby this red circle which for simplicity we'll call the "Skin Tone Region". The area resides along the I line on the Vectorscope and above the Q Line (see the intersecting lines on the graphic below). Where the Q Line crosses the I Line, skin tone saturation is at zero. The closer the skin tone information is to the boundary of the circle, the greater its saturation. Smart camera software such as Skin Tone Detail Circuitry knows to look within the Skin Tone Region and is thus able to isolate the information there to make independent adjustments. This is very helpful because it becomes easier to predict how the values are going to move around on the vectorscope as adjustments are made to the camera.

Now before we start playing, let's get a better idea of how these variables will affect actual human skin by using the DSC Labs CamBelles chart. Obviously sitting models would be better but for what it is, this chart is incredibly precise and I've used it to paint looks in the studio that have worked perfectly well in the field.

The lovely ladies of DSC:

There is a good variety of skin tones here and the light in the scene is modeled enough that you can examine a good range of values. Also the fact that they're wearing bright clothes and are on a blue background helps to isolate the skin tones on the vectorscope.

Here's what they look like on the Vectorscope:

This isn't a tutorial on tonality but part of getting good colors means getting a good exposure. This is what my properly exposed and properly white balanced CamBelles look like on the waveform.

And if you have False Color on your monitor, you can use it to confirm your exposure:

Usually you want to keep it in the green-yellow zone for light skin tones and green-blue for dark. Orange is 80% which is where skin starts to break up so you definitely don't want your key light hitting that hard.

Skin tones can also be affected globally with Master Saturation Controls. Increased Saturation on the left and decreased Saturation on the right:

Part 2: User Matrix menu and skin tones

Typically you wouldn't use matrix adjustment to specifically affect skin tones as these are more global adjustments but it's good to see what the effect is. You're also hardly ever going to only use one of these adjustments. When creating a custom look, you'll most likely be pushing values around in all six menu options.

For example, let’s look at a side by side of the Cambelles when you put the G-B (Green into Blue) attribute at its maximum value, +63 on the left and its minimum value, -63 on the right:

As you can see, you’re never only affecting the skin tones. In your quest to render the perfect skin you’re also affecting plenty of other colors. It’s very easy to get caught in an endless cycle of color correction where you fix one thing only to create a new problem with another color. Only through trial and error and understanding the basic principles behind how in-camera color correction works will you be able to quickly execute the best solution.

Now let's have a look at both what happens to our skin tones when we adjust each of the user matrix variables:

B-G, BLUE INTO GREEN:

On the left - Positive Value, In the middle - Default Value, On the right - Negative Value

B-G +63 (increase in value)

B-G –63 (decrease in value)

B-R, BLUE INTO RED:

On the left - Positive Value, In the middle - Default Value, On the right - Negative Value

B-R +63 (increase in value)

B-R–63 (decrease in value)

G-B, GREEN INTO BLUE:

On the left - Positive Value, In the middle - Default Value, On the right - Negative Value

G-B +63 (increase in value)

G-B –63 (decrease in value)

G-R, GREEN INTO RED:

On the left - Positive Value, In the middle - Default Value, On the right - Negative Value

G-R +63 (increase in value)

G-R –63 (decrease in value)

R-B, RED INTO BLUE:

On the left - Positive Value, In the middle - Default Value, On the right - Negative Value

R-B +63 (increase in value)

R-B –63 (decrease in value)

R-G, RED INTO GREEN:

On the left - Positive Value, In the middle - Default Value, On the right - Negative Value

R-G +63 (increase in value)

R-G –63 (decrease in value)

Part 3: Color Correction menu and skin tones

Unfortunately I don't have CamBelles examples for working with the Color Correction menus. The attributes you'll be working with the most in regards to skin tones are the following three video colors: Red-Yellow (Yl-R), Red (R), and Yellow (Yl).

In the Color Correction menu set, we can isolate and modify the following twelve individual vectors: six primary video colors - Red (R), Yellow (Yl), Green (G), Cyan (Cy), Blue (B), and Magenta (Mg) and the six colors in between the primaries - Red-Magenta (R-Mg), Magenta-Blue (Mg-B), Blue-Cyan (B-Cy), Cyan-Green (Cy-G), Green-Yellow (G-Yl), and Yellow-Red (Yl-R).

As exemplified in the above graphic, the colors in and around these areas will be affected by their corresponding adjustments. To modify the Hue or Saturation of Red, use the "R" Color Correction attribute, for the colors in-between Yellow and Red, use "Yl-R", etc.

These Color Correction attributes are modified with a Phase and Saturation control. A negative Phase value (-) will move the color to the left on the vectorscope, a positive Phase value (+) will move it to the right. A negative (-) Saturation value will move the color closer to the center of the vectorscope, decreasing saturation and a positive (+) value will move it closer to the edge of the circle, increasing saturation. By altering the Phase on an individual color you are moving it out of alignment with other colors and reducing the amount of shades the camera can reproduce. Using these controls you can work on individual colors (such as skin tones) and subtly alter their hue and saturation but you still will affect any other color that contains the color you are modifying. The effect is far more subtle than the Linear Matrix adjustments, however is often necessary to arrive at a very specific hue or color saturation. Color correction in post production allows for a much finer degree of control so in some cases, it's best left to them.

As mentioned in the previous article, you're very rarely only going to work with one attribute at a time. It's really understanding how they're all used together that's the key to good camera painting. Every task is different and there is no "one size fits all" approach. However I will Yl-R in Color Correction is often where I start when trying to inject some warmth and life into dull looking skin. Please support this blog by leaving comments and feedback. It's really only through user support and feedback that content can be fine tuned so I always appreciate hearing from you.

January 05, 2014

Painting HD Cameras - Basic Colorimetry

January 05, 2014/ Bennett Cain

Painting HD Cameras - Basic Colorimetry

Technical Notes:

The images used in this article were created with a Panasonic HDX900 and the stills / vectorscope information was captured with a Leader LV 5330 Multi-SDI Monitor. Because a Panasonic camera was used, the workflow presented and menu features explained are those found on Panasonic cameras. The menu set on Sony cameras is similar enough though that I feel that if you know one system, you should be able to apply the same concepts to the other. The chip chart used was a DSC Labs Chroma Du Monde 28R CamAlign Chart. These charts are the standard for video engineering and camera alignment. Because the colors and values are so uniformly printed and tested, they can be measured electronically with repeatable results. Correct use of DSC Labs equipment can not only be used to calibrate and match equipment but to paint custom looks in the controlled environment of a studio. The GAIN on the Vectorscope images was set to x1. When doing critical camera matching or alignment with the Chroma Du Monde, it is recommended that you set your Vectorscope Gain to x2. For the purposes of this tutorial, I felt that keeping the Gain at it's default value of x1 best illustrated how to read the scope in the field and objectively evaluate color saturation.

Part 1: Overview

In this article we are going to use the video camera's Linear Matrix (also known as Matrix Table or User Matrix) and Multi Matrix (also known as Color Correction) menus to modify its colorimetry, which is the way the camera renders specific colors within its video color space which for HDTV is ITU-Rec. 709.

ITU-Rec.709 Video Color Space (from Wikipedia):

Please refer to the Wikipedia article for a detailed account of the above graphic.

The combined use of both the Chroma toolset (explained here), the Tonal Response Controls, i.e., Gamma, Knee, Pedestal, and Detail Circuitry is necessary to really "paint" a HD camera. There are a ton of tools at your disposal in a video camera's Paint menu and only through lots of trial and error and the use of a calibrated reference grade monitor can one learn to use them correctly.

In order for any of this to make sense one needs to know the nomenclature. Colors are referred to as Hues in engineering lingo and Phase refers to the relative position of the color as plotted by a line on the vectorscope. For simplicity, in this tutorial I'll be referring to colors as "colors" and not "hues". For describing a video camera's colorimetry, Japanese engineers have come up with a way of describing the six specific color phase adjustments we can make and those are G-B, G-R, B-G, B-R, R-G, and R-B.

“B-R” is read as: Blue ADDED TO Red which affects all colors MOST NOTICEABLY Blue, LEAST NOTICEABLY Red. A positive value increases the Saturation of Blue added to Red. A negative value decreases the Saturation of Blue added to Red.

“G-R”, is Green into Red. “B-G”, is Blue into Green, etc. With B-R, you are adding or subtracting Blue into or from the Red channel. G-R, adds/subtracts Green to the Red Channel. You get the idea.

The two colors that form the pair, i.e., B-R, are linked and therefore these adjustments will always change these two colors and often a third or fourth color as well. Generally, all colors are affected slightly, some radically.

These adjustments can be used to make colors punchier or more exaggerated, more saturated or de-saturated, create unique looks, or match one camera to another.

There is a finer point though –

One might think at first that by adding Blue to the Red channel, Red is going to get Bluer when in fact it has the opposite effect – Adding Blue to Red pushes it closer to its neighbor, Yellow, which makes all Red colors in your image become more Orange because that's what you get when you add Red and Yellow. It's actually basic color theory.

The way changing the Linear Matrix works on HD video cameras is you affect a color by pushing or pulling it into an adjacent color space and all colors are linked to the one opposite them. That said, you can make Red's look more Magenta or more Yellow but you can't turn Red into Green. It just doesn't work like that.

In video colorimetry, each color has a relationship with both its neighbors and its compliment on the other side of the scope. Really not much different than a color wheel used to teach art foundations.

If the naming conventions seem complicated, fret not because fortunately this tool set is essentially the same on every HD video camera. They make the visible colors in their color gamut from six primary video colors: Red, Blue, Green, Cyan, Magenta, and Yellow. This differs from traditional color theory somewhat in that there are three primary colors and three secondaries which are made from them.

As you can see there are six colors represented. In the center of the scale is the “chroma free” zone. This area is neutral and colors close to it are very de-saturated and pastel. You can also tell if an image has been correctly white balanced when the concentration of this neutral picture information is centered on the scale. Colors increase in saturation as the move away from it towards the outer edge of the circle. Colors that leave the circle are “out of gamut” and aren’t broadcast legal. White Balance is an extremely important factor in digital imaging. For colors to appear "correct", meaning colors that look natural to your eye, your camera must be white balanced. White balance is a global control and moves your entire chroma information in between the red/yellow - blue/cyan axis. Creative use of white balance is an important tool at your disposal in artistic camera painting.

You can tell these images are properly white balanced because the neutral information is exactly in the center of the scope. On the left is an image with enhanced color saturation. The vectors are approaching the edge of the circle and the colors are extremely saturated, our Yellow has actually wandered "out of gamut" and is no longer broadcast legal. On the right is a very de-saturated image whose color information is close to the neutral center of the circle.

This is great because if you learn how to paint one camera you can basically paint any camera that has a User Matrix and Color Correction menu. That’s the nice thing about digital HD video – despite its many different flavors it’s all essentially the same.

All User Matrix menus have the same six adjustable attributes: B-G, B-R, R-B, R-G, G-R, G-B. You can use these menu adjustments to subtly or radically alter the color characteristics of your image. The User Matrix and Color Correction does NOT affect the camera's Tonal Response which is White, Gamma, or Black levels.

I've heard a video camera’s Linear Matrix likened to a film stock. I like this because just as film stocks have very specific responses to individual colors, so does a video camera’s colorimetry. That said you ordinarily wouldn’t change film stocks in the middle of a scene so a similar attitude toward the matrix is generally recommended. You can quickly end up with mismatched images if you start painting away like crazy so a good eye for continuity can’t be overstated. That isn’t to say you can’t do it but proceed with a light touch because matrix adjustments are baked into the video image and are often times irreversible.

As you’ll see in the examples below, there is no way to single out one individual color with the User Matrix adjustment tools. However, you can use the Color Correction menu toolset to more closely isolate and adjust individual colors within the Linear Matrix. You can't single out a specific color though as any other color that contains this color will also be affected. Always check the entire scene to gauge the effect.

In my experience, I use the User Matrix tools for the following:

-Camera matching or emulating the color response qualities of another imager such as a film stock or a CCD chipset from another manufacturer.

-Emulating a specific look such as Bleach Bypass, Day for Night, or some sort of Color Filter effect.

-Creating a base colorimetry or color response for a specific scene or project.

I use the Color Correction menu tools for:

- Adjusting the Phase and Saturation in the Yl-R Color Correction attribute is a great way to make fine adjustments to skin tone hue and saturation.

- Working on a specific color that needs modification. Often times with product shots, there is a very specific hue and saturation that must be followed.

- Fine and subtle color correction. As the name implies, the Color Correction menu can in fact be used this way however it can be an intense process and there is rarely the time on-set to spend on it so you're better off painting various looks in pre-production or at the checkout and modifying those as you go. Just be sure to keep everything within the limits of the legal gamut and don't throw colors completely out of phase and won't make things any worse.

In a nutshell, the User Matrix is more for broad strokes whereas Color Correction is for small. Ultimately though, you're always going to be using them together to arrive at the desired effect.

Part 2: Getting into the User Matrix menu

Within the “Paint” menu on the HDX900 you will find a menu called “Matrix”. Within it you will find the six attributes I mentioned that are adjustable in both positive and negative increments. On the HDX900 these increments max out at 63. On Sony cameras, I believe they max out at 99. At any rate, in practice it’s all the same. The comparison for each attribute is a value of 0 versus a maximum value of either +63 or -63.

Here is a waveform of our basic, uncorrected Chroma Du Monde chart:

A correct exposure for the Chroma du Monde chart is indicated by exposing the 11 step grayscale so that is crosses at 60 IRE.

The importance of good exposure to camera painting can't be understated. Without good exposure, you don't have much to work with so start by ensuring your image is properly exposed.

USER MATRIX ADJUSTMENT EXAMPLES:

1. B-G, BLUE INTO GREEN:

On the left - Positive Value, In the middle - Default Value, On the right - Negative Value

B-G +63 (increase in value)

B-G –63 (decrease in value)

2. B-R, BLUE INTO RED:

On the left - Positive Value, In the middle - Default Value, On the right - Negative Value

B-R +63 (increase in value)

B-R–63 (decrease in value)

3. G-B, GREEN INTO BLUE:

On the left - Positive Value, In the middle - Default Value, On the right - Negative Value

G-B +63 (increase in value)

G-B –63 (decrease in value)

4. G-R, GREEN INTO RED:

On the left - Positive Value, In the middle - Default Value, On the right - Negative Value

G-R +63 (increase in value)

G-R –63 (decrease in value)

5. R-B, RED INTO BLUE:

On the left - Positive Value, In the middle - Default Value, On the right - Negative Value

R-B +63 (increase in value)

R-B –63 (decrease in value)

6. R-G, RED INTO GREEN:

On the left - Positive Value, In the middle - Default Value, On the right - Negative Value

R-G +63 (increase in value)

R-G –63 (decrease in value)

Part 3: Getting into the Color Correction menu

All Color Correction menus allow the same six components of the Linear Matrix plus six additional in-between components to be individually adjusted. They are: 6 primary video colors - Red (R), Yellow (Yl), Green (G), Cyan (Cy), Blue (B), and Magenta (Mg) and the 6 colors in between the primaries - Red-Magenta (R-Mg), Magenta-Blue (Mg-B), Blue-Cyan (B-Cy), Cyan-Green (Cy-G), Green-Yellow (G-Yl), and Yellow-Red (Yl-R)

These Color Correction attributes are modified with a Phase and Saturation control. A negative Phase value (-) will move the color to the left on the vectorscope, a positive Phase value (+) will move it to the right. A negative (-) Saturation value will move the color closer to the center of the vectorscope, decreasing saturation and a positive (+) value will move it closer to the edge of the circle, increasing saturation. By altering the Phase on an individual color you are moving it out of alignment with other colors and reducing the amount of shades the camera can reproduce. Using these controls you can work on individual colors (such as skin tones) and subtly alter their hue and saturation but you still will affect any other color that contains the color you are modifying. The effect is far more subtle than the Linear Matrix adjustments, however often necessary to arrive at a very specific hue or color saturation. Color correction in post production allows for a much finer degree of control so some cases, it's best left to them.

For the sake of simplicity, the goal of this first Colorimetry tutorial is to show how these controls work. It's rare that you'll only use one attribute at a time to color correct a scene. The hard part is knowing how these controls can be used together to create custom looks. But if you know what each one does, you can predict how they will work together and a skillful well practiced hand at the paint box can create some remarkable images.

If there are any errors or omissions, please bring them to my attention. These tutorials need reader feedback to be effective learning tools so if you have something to add, please don't be shy.