How much of a difference do different color spaces make?

Question

How much of a difference does it make to use one of the extended colorspaces vs. the normal sRGB? And what difference does it make?

Are there situations where it is not important, and conversely are there situations where using an extended colorspace is essential?

Answer

Color spaces, as ysap stated, can be a confusing issue. There isn't a single correct answer to this question, and what you intend to do with the "final copies" of your images will really dictate what color spaces you use and when you convert from one to the other.

While I think it is getting a bit dated, sRGB is still the "safest" color space these days. Many professional printing services require sRGB for print (although that is changing these days, as many professional printing services now support AdobeRGB or even ProPhoto RGB). If you are publishing your images to the web, sRGB is also the safest color space to convert your final images to, as many web browsers do not support proper ICM, and default to rendering in the sRGB space.

What color space you use during your processing workflow, on the other hand, is a more complex story. First off, camera's see far more into the realm of green color than computers or printers can generally render. If you work in RAW, and want to preserve as much original color accuracy as possible throughout your workflow, it is best to keep your images in the widest possible gamut. If you are working with muted scenes, or scenes with limited color, particularly lower saturation, a narrower gamut will be ideal. Use of a wide gamut when processing RAW is usually done for you if you use a tool like Lightroom or Aperture, as those tools make the default assumption that RAW images will utilize a considerable amount of the ProPhoto RGB gamut...the only gamut that covers nearly the entire LAB space that represents human color perception. Converting from RAW to TIFF will, then by default, save TIFF images with ProPhoto RGB unless you choose otherwise. (When working directly in RAW, gamut is really not taken into account, as RAW images are generally not tagged with a gamut at all.)

Modern professional photography hardware, both computer screens and printers, have all moved towards AdobeRGB as the base or reference gamut. Top of the line, and even middle grade, LCD screens like the Apple CinemaDisplay, NEC, Eizo ColorEdge, or LaCie 700 RGB-LED series monitors all support 98-123% of the AdobeRGB gamut. Modern printers from Epson and Canon, particularly the prosumer models, but now also the professional/commercial lines, also support 98% or more of the AdobeRGB gamut. Epson printers tend to cover more of the blues and violets beyond the realm of sRGB and AdobeRGB, while Canon covers more of the reds and greens beyond the realm of sRGB and AdobeRGB. Therefor, if your intention is to process your photos on a professional grade wide-gamut LCD screen and print your photos on a prosumer Epson or Canon printer, the AdobeRGB gamut is the ideal choice for your final images.

Converting from a wide gamut to a smaller gamut can be a critical step in your workflow. There are a variety of rendering intents when converting between color spaces. The two most common are Relative Colorimetric intent, which aims to preserve original color value accuracy at the cost of perceptual accuracy, and Perceptual intent, which aims to preserve perceptual accuracy at the cost of original color value accuracy. Converting from one gamut to another should be done as infrequently as possible. Ideally, you would work in RAW until the moment you generate a "final copy" image for a specific medium, at which time you would convert that final copy to the appropriate gamut. If you are saving for web, the best gamut is sRGB. If you are saving for print, I would choose AdobeRGB unless you are sending off to a print lab for print, and they require sRGB.

When converting, it is important that you have your white and black points, curves, and contrast set correctly for. If you are converting to sRGB for display on the web, white and black points are far less important. For print, it is best to try soft proofing your image and tweak white and black points first before converting to a final gamut. You should convert and compare the original image to the converted image, and make sure you have not lost vibrancy or saturation in key areas. When converting from a wider gamut to a narrower gamut, the key areas where you may lose color will be in the greens and deep blues. If the difference between a source gamut and destination gamut color is broad, especially if that particular color is found in gradients, you may encounter some posterization or clipping. In such cases, you may want to adjust saturation, white and black points to reduce the range of color you are utilizing in your original image. This will lessen the amount of compression of color into the destination color space, and mitigate or eliminate posterization and clipping.

For a few general rules of thumb:

• Cameras "see" a much wider gamut with their sensor than computer screens or printers can render. Particularly greens.
• If you shoot vibrant, saturated scenes, a wider gamut will preserve colors better.
• If you shoot muted or desaturated scenes, a narrower gamut will preserve colors better.
• Most professional photography computer screens and printers support the AdobeRGB gamut.
  • Computer screens cover 98% - 123% or so of AdobeRGB
  • Printers cover around 98% or so of AdobeRGB, with different brands covering extended saturation into blues, violets, oranges, reds, and greens.
• Saturated green is one of the primary colors lost when converting to a narrow gamut, with blue and red following.
• The key difference between wide and narrow gamuts is their chromaticity.
  • Chromaticity generally refers to the hue and overall saturation of a color...its purity
  • Wider gamuts reach greater chromaticity
  • Narrower gamuts reach lesser chromaticity

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What's the difference between Adobe RGB and sRGB and which should I set in my camera?

Question

In my Canon 60D, there's a setting between Adobe RGB and sRGB. What's the difference and what should I prefer when shooting to RAW ?

Answer

sRGB is the most common color-space used anywhere.

AdobeRGB is a wider color-space which can represent more colors but with less precision when looking at the colors which overlap sRGB.

Neither color-space really matters when shooting RAW.

The embedded thumbnail or preview within a RAW file may be affected by the choice of color-space though, so keeping sRGB selected is usually the most sensible thing to do.

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How do color spaces like sRGB and Adobe RGB overlap?

Question

Is sRGB included in Adobe RGB, and Adobe RGB included in ProPhoto RGB? Meaning that a photo in a "lower space" will look like exactly the same in a "higher space", e.g. a sRGB photo will look like exactly the same in a Adobe RGB space.

I noticed the size of a sRGB photo is bigger than the same one in Adobe RGB, which I don't understand since the color space is bigger.

Answer

Check out this image by Jeff Schewe from wikipedia. It's a 2D projection of what's really a three-dimensional space, but it makes the basic concept clear:

So: sRGB is a subset of AdobeRGB, which is a subset of ProPhoto RGB.

You can also see how ProPhoto RGB extends outside of the curved shape which represents visible colors. And you can see how AdobeRGB is a better fit for printing on matte paper than sRGB — and how far outside what can be printed on paper the ProPhoto space extends.

But this isn't the whole story, because of the issue of bit depth. Color information is stored in integers, not analog values — there's a discrete, countable number of colors that can be described at a certain bit depth. Think of the color space like a box of Crayola crayons of different colors. Each color space has the same number of crayons. In the larger spaces, some of that limited number has to be used up for the wider coverage — in ProPhoto RGB, you've got a number of "crayons" devoted to colors that humans can't even see. sSGB has the same number of crayons packed into a smaller range. That means, in exchange for not being able to represent those far-out cyans and greens, you get more fine distinction between the blues and purples and reds (and the greens which are there).

In 8-bit-per-channel color depth (24 bits overall), there's about 16.8 million crayons, which is a lot, but enough that there's still a chance for color artifacts in subtle gradients. And, when you map from one color space to another, the crayons don't necessarily line up. ProPhoto RGB may contain all of sRGB, but if you're working in 8 bits, it's lossy to go back and forth.

Imagine that you've got three different shades of red in one crayon box, and two shades of red in a different box (because that second box needs the extra crayon for ultramarine). If you're trying to duplicate a picture drawn from the first box, you have to compromise on your rendition of red. And if you then go to make another copy with your first crayons but without looking at the first image, you'll probably not pick the same mapping from those two reds to the more expressive three.

However, if you can work in 16 bits per channel, this is really not an issue. That's because for each crayon in 8-bits-per-channel, 16 bits gives you 16.8 million crayons. That's a lot of subtle gradation — almost certainly beyond what the human eye can distinguish. (The overall number of distinct colors in 16-bit color depth is over 281 trillion.) So, if you're using an application like Adobe Lightroom that works in 16 bit color depth, switching color spaces isn't a concern — but you do have to decide what compromises you want when you want to go down to a final output value, because we don't really have good, standard, popular, well-supported 16-bit high-gamut-color-space file formats yet.

As for the size of the resulting file: that's basically just going to be a quirk of how the compression worked out. The actual span of the color space makes no difference in the file size, since, again, same overall number of crayons in any case. It's possible that your sRGB photo is bigger because the Adobe RGB version "collapsed" some of the subtle color distinctions into the same value (not enough different kinds of red crayon?). But it's probably just a quirk of how the "reassignment" of crayons causes the data to be different and therefore the compression to be different.

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Why do JPEGs only look right when exported from Lightroom in sRGB color space?

Question

When I export RAW photos (Nikon D5000 NEF photos converted in DNG format by lightroom) as JPEG, the only way to get the same color as the original photo is by setting the sRGB color profile in the JPEG export options.

Setting ProPhoto or Adobe RGB gives me different results than the original. And when I open one of those RAW photos with Photoshop, it says the RAW photo incorporated profile is ProPhoto RGB. So shouldn't ProPhoto be the best color profile to use? But why can't I export them using ProPhoto RGB or Adobe RGB color space?

My screen is correctly calibrated on Adobe RGB.

Answer

I expect you are looking at the exported JPEG photos with some program which does not properly take the color space into account — it just assumes sRGB, the standard default. So, only your photos exported to match that expectation work. (Even if your screen is calibrated, your applications might not be so smart.)

Keep in mind that Adobe RGB is a color space mainly optimized for print. While monitors are getting better (and yours may qualify as better), most consumer-grade ones can't cover the whole gamut anyway — there are colors that just can't be shown, so they're "clipped" to colors within the monitors' natural/native color gamut.

This isn't part of your question, but:

ProPhoto is a very large color space designed to be a working space, not used for final results. It's very big, and in fact not only exceeds what your monitor can show but contains "imaginary" colors (that's the technical term) which don't correspond to anything in human vision. That's good for a working space, because you don't accidentally clip colors in the midst of curves adjustments and etc., but it's not very useful for a final format. In fact, it's particularly poor for 8-bit-per-channel JPEG images, because there's only 256 possible values for each channel, and when those are spread out so far and "wasted" on imaginary colors, you have less data for real colors, possibly making posterization an issue in gradients.

So, back to the question: you should save your images in a color space based on the intended display. In the current world, that's largely sRGB, unless you're making your own prints or working with a lab that provides printer-specific color profiles for your use. Adobe RGB may also be an option, but your viewing/presentation choices will be more limited (and I think that's what you're running into here).

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What's the difference between Adobe RGB and sRGB and which should I set in my camera?

Question

In my Canon 60D, there's a setting between Adobe RGB and sRGB. What's the difference and what should I prefer when shooting to RAW ?

Answer

sRGB is the most common color-space used anywhere.

AdobeRGB is a wider color-space which can represent more colors but with less precision when looking at the colors which overlap sRGB.

Neither color-space really matters when shooting RAW.

The embedded thumbnail or preview within a RAW file may be affected by the choice of color-space though, so keeping sRGB selected is usually the most sensible thing to do.

Check more discussion of this question.