What exactly is Adobe RGB?

[Senor Hound]

I look at what it is and it says its a coloring system that has a broader array of colors that Standard RGB or sRGB. That sounds great, but then it also says that monitors and printers use sRGB and that using Adobe can throw off your colors. So, which one should someone use when photographing? I know it will depend entirely on what a person is shooting, but if you wouldn't mind explaining it, I'd appreciate it.

 

[Bifurcator]

Adobe RGB (Aka: Adobe 1998) is an RGB color space and it sounds like that's you're real question here. Adobe RGB's primary advantage over other color spaces though is that it can be used as a very good CYMK representative or substitute - err, I mean it covers most of the CYMK colors that other RGB color spaces do not.

OK, so what's a RGB color space? Well, to understand that it might be useful to know what a color gamut is. Hehe, this could get very deep and books have been written to explain it. While it would be great to read one or several for a full understanding we can get the notion across more simply and in shorter order by asking what 100% Red (or green or blue) is to each one of us. With my opinion or "gamut" of what 100% red, green and blue are assuming I have an 8 bit opinion of each color, 16,777,216 colors are possible. This is called a color pallet. And this then is the Bifurcator color space expressed in a 24 bit pallet. Now as we ask a different person what 100% red, green and blue are to them and get slightly different answers we will get different colorspaces that differ slightly or dramatically across that same pallet - depending on their opinions. If we replace "people's opinions" here with manufacturers component characteristics of any given device we can see where color spaces and gamuts come from.

If your camera sensor is a superset (let's say it has a 12 bit opinion of the three color components) and you wish to output (display) accurately what it's seeing you can choose a color space that more closely matches the intended 8 bit output device or by mutually agreeing upon a common color space.

Which one a person should use when photographing? The best imo is to use RAW and then later assign one of the subsets. The most popular by far and the default in most applications that do not support multiple color spaces is sRGB so that would be the best for web display probably.

EDIT:
If you want to know more the best search option is to use google and specify a filetype of PDF like "filetypedf rgb colorspace". This will bring up all the white papers that the books I mentioned should be referencing. Probably the second best is to use Wiki which usually links to a minor few of the same white papers in the reference link section. But I've noticed and corrected lots of wrong information on computer science in general (and computer graphics in specific) on Wiki.

 

[Senor Hound]

Okay, that makes sense. But I have another question.

Adobe RGB serves little to no purpose if the display device (CRT monitor, printer, etc) doesn't support it, right? Cause it will only be able to read the typica sRGB 0-255 rating, and will do funky things to the rest?

I would really (now) like to know how you can tell if a printer supports Adobe RGB in its transition to CMYK, or if a monitor does in its reproduction.

Thank you so much for responding. I know now that maybe this isn't a beginner's question as I thought it was!

 

[Mav]

You need to know exactly what you're doing to use Adobe RGB effectively, otherwise you'll get duller colors. I've seen this recommended as the default setting on some D200 setup chart posted somewhere on another forum, and this is probably the worst advice I've ever seen given on one of these forums. Just stick with sRGB unless you really know what you're doing and do your own printing also, or get stuff printed at a place that will do Adobe RGB. sRGB is the world standard.

 

[Senor Hound]

You need to know exactly what you're doing to use Adobe RGB effectively, otherwise you'll get duller colors. I've seen this recommended as the default setting on some D200 setup chart posted somewhere on another forum, and this is probably the worst advice I've ever seen given on one of these forums. Just stick with sRGB unless you really know what you're doing and do your own printing also, or get stuff printed at a place that will do Adobe RGB. sRGB is the world standard.

THANK YOU SO MUCH! I have learned so much between you guys and other sources I've been searching. You guys have provided me with the few missing links I had to put it all together in my head. I feel so enlightened!

Is there a way to find out who can print photos in Adobe RGB? Well not print, but read it to print off the appropriate colors? Also, I wanna know how you can edit a photo that was shot in Adobe RGB if your monitor can't even decipher the extra colors its producing.

BTW, I'm not gonna mess with it, but I just want to know for my own sake.

 

[Bifurcator]

Okay, that makes sense. But I have another question.

Adobe RGB serves little to no purpose if the display device (CRT monitor, printer, etc) doesn't support it, right? Cause it will only be able to read the typica sRGB 0-255 rating, and will do funky things to the rest?

I would really (now) like to know how you can tell if a printer supports Adobe RGB in its transition to CMYK, or if a monitor does in its reproduction.

Thank you so much for responding. I know now that maybe this isn't a beginner's question as I thought it was!

Well, most LCDs - especially the under $1,000 guys are "doing funky things" to all the profiles anyway as they use dithered 18-bit color (64 × 64 × 64 = 262,144 color pallet). But if they can use a "mutually agreed" upon predefined color space then it's better. Check the manuals for what they say they support.

sRGB is a CRT gamut I believe and is derived or based on a daylight simulator sampled in western (?) europe at noon - true story! It's technically correlated to the color temp 6504K but everyone (makers) just calls it 6500K. It's a conglomerate spec that is supposed to or that tries to include and merge all things "TV" and "PC".

Pretty much all monitors, personal high-color printers (like ink-jets and etc.), and scanners are within or can use the sRGB profile. I think if I remember right HDTV is based on it as well. "Based on it" heh, there's so much I'm leaving out here - but I guess that's a good attempt at simplifying things. Hehehe, sRGB is the standard color standard.

Also know that if all your equipment can do one specific standard then it's ok to work in that standard - standardly And you won't have to know anything specifically about it. Pretty much everything "PC" can do Adobe RGB, Apple RGB, sRGB, ColorMatch RGB, and a few others too I guess. So you can set your camera to any of those and if you're shooting RAW it doesn't matter - or shouldn't afaik anyway!

 

[Helen B]

This is quite a big subject, so you will probably get it a bit at a time from different people.

There are two interpretations of 'printing in Adobe RGB'. One is that the printer (a physical object, or a company) can handle files tagged with Adobe RGB and another is that the gamut of the print will match the gamut of Adobe RGB. The latter isn't going to happen, the former could happen.

Here is an example that might help to clarify the issue. I expect that you will have more questions...

This is the envelope of the gamuts of Adobe, sRGB and the Epson 3800. The Epson 3800 is, in reality, a CMYK printer, with a fairly large gamut for a CMYK printer (not the greatest, but not the smallest). The 'envelope' means that the diagram shows the colours that are farthest from neutral, irrespective of the brightness of the colours. (It's really a top-down view of a three-dimensional graph)

You can see that Adobe RGB has a wider gamut than sRGB and that neither of them match the shape of the gamut of the 3800. The printer fails miserably in the pure reds, greens and blues (especially blues) but does quite well in the yellows and cyans. No surprise. It is using what is basically a CMYK ink set, and the C, M and Y inks are not perfect.

Now look at the gamuts in the darker colours. This is at a single brightness corresponding to L*=30, ie what would be perceived by a human as equal to a 30% grey (not 30% reflectance, but perceptually 30%).

Ignore the dots in this graph.

This shows that the 3800 is doing very well in most colours, but still failing miserably in the blues. Its gamut exceeds both Adobe RGB and sRGB in the green-cyan region.

Now look at the lighter colours, at L*=73.

Now the 3800 is closer to sRGB than Adobe RGB, but is still failing in the blues.

The printer cannot print the full gamut of either sRGB or Adobe RGB, but if it gets a file in Adobe RGB it has the potential to print a wider gamut than if it gets sent an sRGB file.

The software handles the conversion between the printer's 'colour space' and the file's colour space - usually by converting to Lab first, then back to RGB for sending to the printer (just to confuse things, many inkjet printers are seen by the printing software as RGB devices when they are really CMYK)

So, in summary, the 3800 cannot print the Adobe RGB gamut, but the software controlling it can handle Adobe RGB files. It can't print the sRGB gamut either.

Good photo editing programs will show you if there are any colours outside the gamut of your display or printing device. In many cases there may not be a big problem. Here, for example, are the colours of a landscape photo (which is in Adobe RGB) shown for L*=53 (ie equivalent to about 20% reflectance). The cluster of dots represents the actual colours in use. Most of the outliers at the edges of the profiles are bugs in the viewing software (now fixed, I hope).

Note that most of the colours are within all three spaces, including the printers - the printer can print all the colours in this file. Had I used sRGB I would have lost some of the saturated yellow-greens, which are quite important in landscape photography. The image may be none the worse for losing them, however.



I'd just like to clarify something that Bifurcator wrote. Colour space is independent of bit depth. An 8-bit file in Adobe RGB has exactly the same gamut as a 16-bit file in Adobe RGB, the only difference is that the colours are described more coarsely in the 8-bit.

There are some large colour spaces that are best described in 16 bits because an 8-bit description would be too coarse, but the overall size of the colour space is not affected by how many bits per pixel per channel are used.

Raw files do not have a colour space assigned to them - they have the colour space native to the camera. When they are converted to an RGB format, they need to be converted to a colour space. You may lose colours when that happens. It may not matter to you. If you work on the Raw file in Lab (as Lightroom does) you won't lose colours until the conversion is made to an RGB space.

Good luck,
Helen

 

[Bifurcator]

Yup, good clarification! Thanks! It's good to have a print person around too!!!

Coarse == funky_things;

 

[Senor Hound]

Helen... your post... ROCKED! I get most of it now. It doesn't matter if you can see the color on your sRGB screen while PPing, because it will show up when you print it out (if the CMYK printer can reach out that far).

Now I understand why adjusting colors in lab would be productive. It seems like the printer may "clip" some colors that are out of its spectrum if you adjusted colors in lab colo, but perhaps this color clipping (I don't know if that's the correct term) is negligible, and editing in lab color is just a way to maximize color no matter what print system you use. Or perhaps editing in lab color isn't to get different colors out of the print at all, maybe its just to more accurately reflect the alterations you want to make to the photo you have.

I also now understand why certain printers are so expensive. It could VERY WELL be worth a lot of money to replicate more colors than an average printer if that was your livelihood. I thought all CMYKs were equal. But I guess not...

Wow... all I can say is wow. I am so psyched to be learning stuff!!!

 

[Helen B]

I'm glad that it helped. It's such a huge subject, and I worry about being able to explain it well enough.

Here are some previous threads on colour space:

link 1

link 2

Best,
Helen

 

[Senor Hound]

My last question is (and you don't have to answer, you've answered enough as is), is how to PP a photo in lab color? How do you know when you go into Curves or something that you're not really messing up something, and your monitor can't pick up on it?

 

[Bifurcator]

I don't know what PP stands for. Seeing it on this forum twice in the last week or so is my first encounter with it. My first guess was PaintsohopPro but that's usually PSP. Photo Process? But that's usually IMP for Image Process. PhotoPaint?, Pixel Process? Puppy Pictures?

 

[Mav]

generic abbreviation for post-processing

 

[Helen B]

My last question is (and you don't have to answer, you've answered enough as is), is how to PP a photo in lab color? How do you know when you go into Curves or something that you're not really messing up something, and your monitor can't pick up on it?

Your monitor will probably show you if you are messing up, because it is showing an RGB conversion from the Lab file. You can also use the gamut warning, if your software has it. Being out of gamut is not always a bad thing because sometimes the results are helpful.

Best,
Helen

 

[Bifurcator]

generic abbreviation for post-processing

Ah, thanks Mav! I knew it was something obvious like that. Where I come from (television/film industry) we just call it "post".

--
Yeah, what Helen said...