sRGB vs. RGB Locked

Started Apr 22, 2013 | Discussions thread
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John King
John King Forum Pro • Posts: 14,941
Re: Shoot RAW, and use aRGB - a colour tutorial

Gidday Renard

Renard DellaFave wrote:

Shoot RAW, or at least aRGB. If you must shoot JPEGs only, use aRGB colour space for everything except posting to the web.

I've been into this issue since Photoshop first added color management (and defaulted to sRGB).  Anyone really curious may enjoy this exhaustive discussion:

Not quite as exhaustive (or as exhausting ... ) as Blatner & Fraser's mighty tome "Real World Adobe Photoshop CS". I have read it, and a number of other similar books from cover to cover. In B&F's case, twice ...

Personally, I don't shoot things that are out of sRGB gamut, to speak of, so sRGB JPEGs are perfectly fine.

As I have already noted, many things are out of gamut for sRGB. These include many flowers and the like, and many man made objects such as the red/orange "Witches Hats" used for traffic control. Also, the aqua coloured canvas so common in the boating and camping fraternities. I could go on, but none of these objects are exactly uncommon. With all due respect, I do not see how you can avoid shooting out of gamut colours using sRGB.

Here is a gamut comparison chart from the aforementioned book by Blatner and Fraser:

My touchstone of colour fidelity is ultimately to compare the print with the original object under as close to the original lighting conditions as possible. However, I also use other measures along the way. Well beyond the scope of the "simple" question asked by the OP.

As others have already mentioned, only relatively high end monitors can display even an sRGB colour space fully. When my wife's Philips sRGB monitor would no longer calibrate decently, I bought another ASUS PA246Q for her computer. It may not be the fastest computer on the planet, but at least it is reliable, and has a decent monitor ...

Speaking of my good lady wife ... She is currently doing a tertiary fine arts qualification. She has a very fine eye for colour as artists have to have, by and large. She is also almost totally "illiterate" as regards technology. When she had to do a unit involving photographing her work and other things to do with her course, I showed her the differences between rendering in different colour spaces and between RAW and JPEG. She could instantly see the differences, and decided then and there to use RAW + LSF JPEGs (simultaneously). All my cameras are set to shoot RAW + JPEG for a number of reasons that seem good to me. Also beyond the scope of this thread.

If I have any special situations, I just shoot RAW and then color space is irrelevant.  What color space to edit in is another discussion, really, and if output is sRGB I see little reason to use 16 bit wide gamut spaces.  The big corrections (if any) are in processing from RAW down to the editing space, so I don't have trouble with banding from doing large 8 bit color corrections.

If it suits you, keep right on doing whatever you are doing. I'm not on any kind of Messianic mission here ... .

The logic of using aRGB for in camera 8 bit JPEG eludes me.  Shooting crater lake and not having RAW as an option?

When one uses the JPEG for all sorts of other purposes (I do), then having decent colour reproduction is critical.

FWIW, there are two things a RAW file does not have, one is a colour space and bit depth, the other is a WB. Having said that, why would anyone want to map a 12 bit RAW file into an 8 bit colour space, and then save it as a JPEG?

FWIW the red car shifting to pink is a problem with rendering to sRGB, not a fundamental problem with the color space. Done properly the out of gamut color would be mapped to the same hue as the nearby reds.  Absolute colorimetric instead of perceptual perhaps?

Like all other colours, the saturated "red" in the car paintwork is actually a mix of R+G+B. From the PPRGB-16 image at my reference point, the 8 bit colour numbers are R=152, B=61, G=36 (C=6, M=100, Y=96, K=1). I have to use 16 bit colour numbers in my web site templates, but these don't come naturally to me ... With the sRGB-16 image, the R+B numbers remain almost identical, but the G value drops to 2 ...

The above shows in the resulting print as a loss of saturation across the whole image, and the red and black in particular have a very marked colour shift.

I have printed this image some 20 to 30 times using all sorts of variations. I note these on the back in pencil. aRGB-16 does a pretty good job, but still fails the ultimate comparison test. sRGB-16 is not even in the ball park. PPRGB-16 comes so close that the final result does not offend one's sensibilities ...

I have also done less exhaustive testing using other images. The results are the same, if not quite as striking. I could equally have chosen plenty of others that contain these sorts of colours. However, when both my own experimentation and the wisdom of authors such as Blatner and Fraser, Schewe & Fraser and any number of other respected writers espouse the same, I am prepared to believe both them and my own eyes.

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Regards, john from Melbourne, Australia.

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