Color Theory

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Color Theory – sRGB vs Linear color space

WHY
Let’s start off by stating everything you know about digital color is a big lie. “What!” you say?. A lie, then how have I been able to produce content this long?

Unfortunately it’s a technical question and a answer.

HISTORY

I’m sure we all have heard of sRGB but what does that mean? We know what RGB is, the three primary colors to make digital images. Almost all image file types have three and/or up to four channels. Red, Green, Blue and sometimes a grayscale channel called an Alpha.

So why don’t we just call it RGB? What is the little “s” that is causing so many issues. Let’s start with a little math quiz. Let’s assume 0 is the absence of red, 0.5 is half red and black and 1 is totally red.

  • Linear : 0 + 0.75 =  0.75 “Red”
  • sRGB : 0 + 0.75 =  0.87 “Red”

But wait why would that happen, a color is a color? To explain it very basically the sRGB format creates a levels curve (just like photoshop) to give more colors variance in the middle while colors closer to black and white are clipped and merged together. Unlike our eyes which dynamically adjust to dark and bright colors monitor and printer cannot produce these colors correctly. So the sRGB format locks the data into a more visually appealing color space.

LUT’s

Let’s first talk about a LUT. So now everything looks washed out, this is where LUT’s come into play. A LUT (Look Up table) is what a digital artist will apply to an image AFTER all the math is calculated correctly. This is done as a “Viewer” only (This is how it should look). For example you can have a: sRGB LUT, per monitor LUT, Film projector LUT, Printer LUT. This will show a linear file in a sRGB format without destroying the data. And destroying data is why it’s important.

Think of it this way: Source (Linear file) + LUT(sRGB) = Result (Correct color space)

Color Space

Now its looks correct but a LUT is only for viewing. How do a save a file with the LUT applied. This is where a colorspace output option is applied. The basic understanding of this is it take what it looks like on my screen and output that. The more complex version is that while it looks fine on your monitor the images may be going to another person and look totally different.

Now why would I have a LUT and COLORSPACE, why can’t I just have a LUT? Well just like monitors and printers each one can produce different colors. In some studios each monitor will have a monitor based LUT. Even the two monitor you may have on your desk are going to be different. Have you ever dragged a image across your two monitors and said “Wow the colors are different per monitor”? Which monitor is correct if the data is baked into the sRGB format. This is again why keeping data linear is important.

Clamping colors

As we strive to make our images more lifelike it’s a good idea to follow what real cameras produce. If you have ever worked with a pro grade camera (Canon or Nikon) you might be familiar with a RAW format. This is just like a digital linear file. Consumer brand camera’s (Point and click, Cell phone cameras) will normally will save a jpeg file that already has a Colorspace applied. Yes your phone has its own LUT and Colorspace output format.

So why is this SO important?

sRGB files (JPEG, PNG, TGA, 8bit files) Vs. Linear files (EXR, RAW)

  • Incorrect color values Correct colors values
  • Colors are clipped to 0-1 (0-255) Colors are not Clipped
  • Only LOOK correct. Needs a LUT to look correct
  • Small File size Large file size

Why it’s important.

So all this under the hood color management takes all the hard confusing work and makes it transparent and allow me to be an artist. Why should I learn digital color theory?

Remember when I said in the beginning everything you know is a big fat lie? So besides what you know is wrong or technically wrong the most important point is the industry as a whole is moving to linear workflows. Movies and television moved a while ago. And now games are adopting the correct theory. The sRGB workflows will become the work of nonprofessionals. Its old, outdated and incorrect.

Does this color theory apply to all work? Yes and no. But you as an artist should understand the why and the need.