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Look at All the Pretty Colors

Many cameras allow the user to tag saved images with either sRGB or Adobe RGB (or perhaps other color profiles). But what this actually does isn't as simple as it might seem.

Most image file formats store color as sets of three numbers, one each for red, green and blue. Without regard to precisely which colors are represented by which numbers, there is clearly a limit on what numbers can be stored. An eight-bit number can only contain 256 discreet values, and three color channels each of which stored as an eight-bit number provides for a mathematical limit of 256 x 256 x 256 possible values collectively. That's 16.7 million possible colors, no more, nothing in between, and nothing beyond the highest number that can be represented. Increase the bit depth to 16-bits per channel and the maximum will increase considerably, but there's still an upper limit to how many colors can be represented. Think of it as a fancy version of the odometer in your car. No matter how many digits may be built into it the counter, at some point, it will eventually reach all nines. You've counted all the way up to the top. Or think of it as being not too dissimilar from counting on your fingers. There's a limit based on how many digits you have. "Digits," get it? But I digress.

There's a common misconception that working in Adobe RGB lets you use more colors than would be the case in sRGB. But the number of possible colors is limited by the bit depth, not the color profile. It's not that some of those precious upper values simply never get used in sRGB and become available only when making the leap to Adobe RGB. Instead of opening up the use of additional colors, the change to a higher gamut color space merely changes how the available numbers get used. The same 255, 0, 0 pure red is simply less intense in sRGB. This is why an Adobe RGB image will look somewhat washed out if incorrectly interpreted and displayed as if it were sRGB. All the numbers for each color channel of each pixel are still there. But they mean something subtly different in different color spaces. Adobe RGB doesn't have more colors, it just allows for the representation of different colors, including those beyond the gamut of sRGB.

RAW image file formats complicate matters in that they don't directly represent color at all and must rely on a proprietary de-mosaic process to interpolate color. But there's still a method to all this raw file rendering madness, and the bits that got recorded by the camera do eventually become color. But unlike with a standard RGB image, the recorded RAW file data isn't in any RGB color space yet. It can't be, given that every RAW file format out there saves only a single color channel and it takes three channels to save RGB data, no matter the profile. sRGB and Adobe RGB both take three color channels and a RAW image has but one channel. A strange one at that, but nonetheless just a single channel.

So, the obvious question at this point would be to wonder just what changing your camera from sRGB to Adobe RGB actually does. Granted, if you are shooting in jpeg, your images will get saved in some RGB color space so its nice that your camera lets you choose. But what if you're shooting in RAW? And you are shooting in RAW, now aren't you? RAW files can't possibly be in any RGB color space, for the simple reason that they have only a single color channel and are therefore not RGB at all. RGB takes three color channels, leaving our RAW file short by a couple of channels.

RAW files won't get rendered in any RGB color space until you load them in Lightroom or some other digital darkroom application, and its not until then that a selection of RGB color space could possibly mean anything. As such, any in-camera tagging as to sRGB or Adobe RGB can only be interpreted as the user choosing a preference for color space to be used later, when you are in front of your computer. Each RAW capture gets tagged with a color space preference of your choice. From there, what happens depends on which program you use. Support for honoring that in-camera color space selection is generally limited to the camera makers native RAW file conversion program. For Nikon shooters, that means Capture NX-D in today's world. If instead, you use Lightroom, Adobe Camera Raw or most any other converter, the profile to be used will typically be based entirely on choices made in that converter program, ignoring the in-camera choice completely.

And whether you can make use of the in-camera color space selection or not, it's really somewhat irrelevant. A RAW file isn't yet in any RGB color space, and it won't be until you convert it. So regardless of whether you specify Adobe RGB, Profoto RGB or any other available profile in-camera or on your computer, that choice will get applied at the exact same point in things. Making the selection at either point in your workflow will result in exactly the same converted results since no earlier choice is truly possible. Or at least no choice could be applied until then. Until then, any choice made will just be waiting in the wings. For all practical purposes, RAW shooters can ignore making a profile choice when setting up their camera. They can, and indeed often must, make their selection later anyway.

How about if you shoot RAW+JPEG? Since this results in two files, just consider them separately. The RAW file will get tagged with your camera setting preference, whether that gets used for anything later on or not. But the resulting JPEG file will get converted in-camera, and that conversion will be done using the selected in-camera color profile. So, one option would be to set your camera to sRGB, giving you JPEG files that are easy to display in sRGB, and RAW files that you can decide to use a wider-gamut RGB color space on your computer.

So, if you're looking to see all those wonderfully pretty colors only possible in Adobe RGB or other high-gamut color space and you shoot in RAW, never mind what you set your camera color space to. Just make sure you pick the intended color space on your computer.


Date posted: July 7, 2019

 

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Related articles:
The Great sRGB Versus Adobe RGB Debate
What About ProPhoto RGB?
 

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