sRGB or RGB that is the question??? comments needed please.

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rongrover
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Joined: Jun 1 2002

Hi. Last week I attended a Colour Confidence Seminar in London. I found it very interesting. But, an issue that came up there was about sRGB being the colour space to use unless you want to end up with a CYMK file output.

Many, includeing myself found this to go against what we had thought to be the better colour space of say Adobe RGB etc. The reasons given for their statement were.

As your monitor (unless you are looking at one cost several thousand pounds) can only show sRGB you can never actually see what an Adobe RGB colour space is. OK, we accepted that. The part that was a surprise that no printer (and they said NO printer) can at present time print out at anything other than sRGB. To print from any other larger colour space it has to convert to sRGB and some printers are not very good at it. They therefore used the logic that in such cases it seems realistic to keep in the one cplour space right through from Capture - Edit - Print. (which incidently was the name and subject of the seminar)

As I said, this did cause much coffee break debate, but it was not really challenged within the presentation. The reason being I am sure was that the presenter was a very well know and experienced person in such subjects.

I have always believed, many from top grade books and articles and not least from the people who have produced printer profiles for me , that at least a colour space of AdobeRGB was best to use. Reading certain reports includeing those about the Epson R2400 which I am waiting delivery of, can handle large colour space. But, it is never as far as I can see, actually stated as such. I have since realised that the main sponsor of this seminar was HP and I seem to recall reading that they are trying to establish the sRGB as a general colour space to use for all digital photo work. The reps HP comment at the Seminar to me was that their printers, even the very top of the range printers costing thousands of pounds, only printed out in sRGB. He showed me prints that were on display there which were printed from a sRGB and other larger RGB colour space (the same photo in A1 size) and pointed out that HP printers performed the conversion to sRGB very well, much better than most other brands, includeing Epson.

So, does anyone know the facts about this subject, what are your thought on it? If, as I suspect it is not a true statement and it was said to promote their sponsor HP, I am not very happy and may well make a complaint (but that is another matter) I am more interested in what the facts are. Incidently I know that many of you use the Epson 2100, and this was really considered a dead cert that it only printed out to sRGB!!

aLL THE BEST, rON.

Alan Roberts
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Joined: May 3 1999

sRGB means two separate things, one good and one very good.

Primaries
The sRGB promaries are those of ITU.rec 709, the primary set for "new and emerging television services". That means digital HDTV to most of us. The red and blue primaries are identically those of the EBU (PAL) colour system, and the green primary lies within the tolerance box for EBU green.

This means that sRGB pictures will look right when you see them on tv, any tv anywhere in the world, provided that tv makes good tv pictures (not all do that, because manufacturers tend to use desaturated primaries in order to get more light, but it's true as a generic statement).

Transfer Characteristic (Gamma)
sRGB uses a far more powerful law than does television, with a much steeper slope near black. So it reveals detail in shadows, and presents saturated colours, much better than does television. That's fine for stills, where noise is stationary, but is hopeless for video where the head-amplifier noise would prevail.

So, sRGB makes a lot of sense if your pictures are going to be viewed on a tv set, anywhere in the world. To a large extent, that includes computers since computer displays mostly use primaries that are pretty close to sRGB or TV (if they didn't, you would have noticed when editing video).

The only issue is the printers. Printer primaries are synthetic since they are generated as secondaries (YMC) rather than primaries (RGB), and they depend on the illuminant (the light under which you view the results). So the printed image is far less controllable than the image on-screen. In general, we assume an illuminant of between D50 and D65 (daylight), but much of printed work is viewed under tungsten or fluorescent lighting, where are the rules get broken.

sRGB is a good way to standardise colour reproduction. It works and is ubiquitous.

My 2 pen'orth.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

rongrover
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Joined: Jun 1 2002

Thanks Alan for your reply. Although it is biased towards TV etc, it was very interesting. As regards photography I feel I will keep to using Adobe RGB. I have however found that the sRGB colour space can be better for skin tones and as most of my work is with portraits will use it at times. Someone at the seminar said just remember sRGB could mean studioRGB, although of course it does not, it is something to use as a prompt!!

However my main issue is as mentioned. Why should such a broard statement be made about sRGB as it was at the seminar? Is it in fact true, I doubt it.

Many thanks Ron.

Alan Roberts
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Joined: May 3 1999

sRGB was introduced as an attempt to unify the multi-media world, that means, tv, computers, and print. Given that tv is the dominant distribution means for electronically produced content, it made sense to unify with it. That's why the reasoning's biased towards tv.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

ashburnham
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Joined: Jul 25 2008

I came across this thread and I know I'm probably going to be ridiculed for bringing up such an old subject but I find this quite interesting and just wanted a quick update.

I am currently scouring the internet forums, blogs and articles to gain knowledge in this field and public liability insurance does not seem to be discussed anywhere else.

I was wondering in the time that's passed since this thread was opened, if technologies or opinions have changed.

Alan Roberts
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Joined: May 3 1999

No real change, except that sRGB is the universal standard for stills these days. The push is now behind HDMI and the newer xvYCC. The jury's still out on that though, I've not enough information to do the sums to find out whether the benefits are worth it.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.