RAW Color Adjustments And Effects

This is the next installment on color and color management. Last time I discussed color charts and ACR camera profiles. I may have given the impression that any old profile will do. Not the case but I wanted to focus more on how you might evaluate different profiles. I hope that you took away the message that evaluating them purely by looking at your screen is not a great idea. I also wanted to convey that that startig point is not the end all be all in the color in your image files.

This time I will focus a little more on some other variables affecting color in your images. Let's start with exposure, brightness, contrast, and ajustments to these without messing with "color stuff". These variables can and do have a huge effect on how you perceive color as well as on the actual image files both at the time of capture as well as tweaks in post processing.

I am not going to go into a disertation on exposure and ajustments and how they might actually impact the colors that come out of your RAW processor in the sence of twisted camera profiles. If you are intrested there are plenty of more scientificly oriented discussion on that. By and large I am going to discuss things that have a major impact where those kinds of effects are secondary from my point of view.

When post processing your images when you apply any of the adjustments that affect brighness or contrast you will end up wth gigantic shifts in the color of your images. When I use the term color I am talking about the aggrigate HSL value - hue saturation and luminance, not just the hue value or the saturation value but all three. In most cases adjusting brightness and contrast will potentally affect all three without ever touching any of the controls that you would usually associate with color like "saturation". Let's take a look at the D7000 color chart from last time.

For the rest of the conversation this is the image that I will be using. Enought words, here is what I am talking about. A simple curves ajustment that would probably not be considered extreme by most peopleā€¦

Huge color difference in a lot of different ways. I plopped color samplers on a few of the color chart chips and left the info window open if you would like to inspect the HSL values yourself. The image is a full resolution screen image if you download it or open it in a new window. To save you some time all three values - the hue, the saturation, and the brightness are impacted to varying degrees with a simple RGB curves adjustment.

The degree of impact depends where on the curve those patches sit compared to where my curve is changed. In most cases the same will be true of most brighness contrast controls that you would use. Exposure, blackpoint, brighness, contrast, levels, you name it. In camera exposure can have similar effects in both actuall values and more importantly perceived colors. Most people would think that only the "B" values would chagnge with the hue and saturation staying the same. Not the case. What changes the most - a slightly different camera color profile or a typical contrast/curves ajustment? You tell me.

I did say "most cases" right. Here is an adjustment to brightness/exposure/contrast that is by and large isolated to only the brightness part of the colors, leaving the hue the same and affecting saturation a little bit less but still affecting it.

The difference is that I set the curves layer blending mode to luminosity. I have to say it again - this is not prescriptive - I am not saying that one is better than the other. It's to show photographers what is going on with their images if they have not looked into it before. I know that most of you do not use Photoshop CS5. I am using it here for demonstration purposes and the ability to display some things like gamut differences. This "Luminosity" blending is actually the only available option when using a curves adjustment in Aperture 3 it's called "Luminance".

Here is a look at a similar curves adjustment using Aperture 3. Of course the images look nothing like each other becuase we started out at a completely different place. It does something similar to Photoshop curves with a blend mode of luminosity.

If you want something similar to the "normal" blending mode in Aperture 3 - all of the rest of the exposure and enhancement adjustment block controls seem to function in "normal" blending mode. The Aperture 3 levels adjustment has the option of either "RGB" or "Luminance". Here is a similar adjustment as above using RGB mode of levels.

Keep in mind when looking at these screenshots that you are seeing effects and not the actual colors in the file nor the colors as rendered on differing ouput mediums. What you are seeing is the colors converted through a particular algorithm/method (we'll talk about this another day) rendered to whatever profile is associated with your screen. That profile whether it is accurate or not is in most cases going to be a smaller color space than the colors represented in your RAW file.

Just to reinforce this - let's look at the colors that are not being represented anywhere near what the file contains based on the first image in the post.

You can compare that to the original out of gamut if you want to.

Last time I talked about color charts and camera RAW processing profiles I may have left you with the impression that they are not important or that I don't use custom profiles. On the contrary they are pretty important and I do make use of custum ACR camera profiles extensively. I don't blindly shoot an xrite colorchecker passport and use the bundled software to automatically generate a profile for every shot or every situation.

The fact is that I use the Adobe DNG camera profile editor with the colorchecker passport chart. The reason for this is that I do not want to use the default Adobe ACR curves that you must use with the colorchecker passport software. I don't like them. Xrite makes some fabulous profiling tools but they are not cheap and I can get what I need using the Adobe tool. As you can see above minor tweaks that occur with most image post processing have much bigger effect than one or two point difference in hues at the RAW decode stage.

I cannot say it enough so here it goes again. You cannot judge a particular camera or profiles "quality" with a quick glance on your typical or even high quality monitor. You need to understand what you are looking at and how it relates to your chosen output medium. Hopefully by the end of this series of articles you will have a good gut feel for what is what in getting from a image file at capture to a final output that you find pleasing. That is the end goal after all. Not some acedemic exercise in color accuracy.

RB

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