RGB For Dummies

[The Kenosha Kid]

What are the advantages of and major differences between the
different RGB levels for PC's listed under the RGB portion of the
color management system of Nikon Scan 4? My version lists
sRGB
Bruce RGB
NTSC[1953]
Adobe RGV[1988]
CIE RGB
Wide Gamut RGB
compensated Wide Gamut RGB

 

[Jim]

What are the advantages of and major differences between the
different RGB levels for PC's listed under the RGB portion of the
color management system of Nikon Scan 4? My version lists
sRGB

Has a narrow gamut which helps with image brightness. It is intended for
computer monitors.

Bruce RGB

A wider gamut RGB invented by Bruce Fraser. It is seldom used these days

NTSC[1953]

A narrow gamut which is supposed to be the standard for television recievers
in the US.

Adobe RGV[1988]

A wide gamut which was developed by Adobe. Best used as a working space
because it encompasses sRGB, NTSC, and Bruce RGB.

CIE RGB

A wide gamut developed by the CIE (standards organization). Not used much
in the US.

Wide Gamut RGB

A very wide gamut standard. Has a large cult following. Encompasses all of
the above gamuts.
Jim

 

[Gordon Moat]

What are the advantages of and major differences between the
different RGB levels for PC's listed under the RGB portion of the
color management system of Nikon Scan 4? My version lists
sRGB

Essentially, the sRGB, Adobe RGB (1998), and Bruce RGB only differ in
the Red and Blue primaries.

Bruce RGB

Originally, Bruce RGB was developed as a work around colour space to
allow heavy editing of 8-bit images. I doubt too many people are still
using this.

NTSC[1953]

This is even more compressed, though a good choice for preparing images
for broadcast usage in North America.

Adobe RGV[1988]

Should be 1998, though in reality that is often the default space for
Adobe products.

CIE RGB

Fairly close match to LaB colour space, though slightly shifted. In
reality, you would be better off with working in LaB, choosing a wider
space, or restricting to a smaller space, depending upon if you know the
final output limitations.

Wide Gamut RGB
compensated Wide Gamut RGB

Encompasses most of LaB, though continues much beyond that in some
regions. Not a bad choice to try to match a CMYK printing space. Most
commercial printers CMYK space (not inkjet, which functions slightly
different) can be encompassed within wide gamut RGB. However, if you are
not careful, it is still easy to get out of gamut colours when printing,
forcing a GCR or UCR clipping to occur in those regions.

Some really great and fairly complete information is available at:

<http://www.brucelindbloom.com/index.html?WorkingSpaceInfo.html>

I will guess that by PC you mean Windows, so unfortunately, there are
some other colour space choices that would not work, like ProPhoto RGB.
Regardless, to play it safe, restrict your choice to a narrower space.
If you want to use a wider space, understand your output media
limitations.

Ciao!

Gordon Moat
A G Studio
<http://www.allgstudio.com> Updated!

 

[Preston Earle]

"The Kenosha Kid" asked: "What are the advantages of and major
differences between the different RGB levels for PC's listed under the
RGB portion of the color management system of Nikon Scan 4?"
------------------------

The advantage of sRGB is that most monitors, most programs, and most
consumer print systems (i.e. Fuji Frontier) output sRGB files without
any surprises. There are some advantages to wider-gamut spaces if your
can display the wider gamut, can understand the "numbers" if you can't
display the differences, and use an output method that takes advantage
of the wider color gamut. For most folks using desktop filmscaners, sRGB
does a fine job. It just doesn't have the snob cachet that wider spaces
have.

I initially used AdobeRGB for all my scans because I thought it was
"better". More experience has taught me that the advantages of AdobeRGB
over sRGB are not worth the risks. I haven't changed over to using sRGB,
but I wish I had started with it four years ago.

Preston Earle
(e-mail address removed)

 

[Bill Tuthill]

I initially used AdobeRGB for all my scans because I thought it was
"better". More experience has taught me that the advantages of AdobeRGB
over sRGB are not worth the risks. I haven't changed over to using sRGB,
but I wish I had started with it four years ago.

My interpretation from reading Photoshop books (chapters about colorspaces)
is that AdobeRGB's principal advantage is that it simultaneously allows
conversion to CMYK for offset printing, and RGB delivery for online use.
If you don't do offset printing...

Apparently although inkjet printers use CMYK (or CcMmYK for photo inkjets)
it doesn't help much to use AdobeRGB, because inkjet printer software
converts from RGB. (Maybe I'm wrong here.)

A problem with digital cameras now is that they have less dynamic range
than print film, so the ProphotoRGB colorspace is sometimes being used
to recover RAW highlights. Seems to work better for this than Adobe RGB.

 

[Hecate]

Apparently although inkjet printers use CMYK (or CcMmYK for photo inkjets)
it doesn't help much to use AdobeRGB, because inkjet printer software
converts from RGB. (Maybe I'm wrong here.)

Sort of. The reason for still using Adobe RGB is it maps to the CMYK
colour space much better than sRGB does. By using sRGB you're actually
limiting the colours you can use more severely.

 

[Gordon Moat]

My interpretation from reading Photoshop books (chapters about colorspaces)
is that AdobeRGB's principal advantage is that it simultaneously allows
conversion to CMYK for offset printing, and RGB delivery for online use.
If you don't do offset printing...

Slight simplification, though often a safe assumption. Unfortunately, Adobe
software is set-up with this as a default, and many people never move off the
default, even some professionals.

Apparently although inkjet printers use CMYK (or CcMmYK for photo inkjets)
it doesn't help much to use AdobeRGB, because inkjet printer software
converts from RGB. (Maybe I'm wrong here.)

Unless you have a printer that handles PostScript colour management, then
there might be little advantage in using CMYK for your files. Often just
keeping the files in RGB colour spaces allows the printer software to
interpret the conversion for the printing inks, though there is no guarantee
that it will always choose the best match. It might take some experimenting,
though you should be able to find a useful and consistent RGB working space
for nearly any printer. Wasting ink and paper is the downside of experiments.

A problem with digital cameras now is that they have less dynamic range
than print film, so the ProphotoRGB colorspace is sometimes being used
to recover RAW highlights. Seems to work better for this than Adobe RGB.

I have been using ProPhotoRGB with scanned film for quite a number of years
already. The benefit is more evident in darker hues and shadow areas, though
some colour ranges also have slightly benefits. The bad part is that most
monitors will not display these values properly, so going by the numbers using
colour sampling is often necessary.

Ciao!

Gordon Moat
A G Studio
<http://www.allgstudio.com> Updated!

 

[Bill Tuthill]

I have been using ProPhotoRGB with scanned film for quite a number of
years already. The benefit is more evident in darker hues and shadow areas,
though some colour ranges also have slightly benefits. The bad part is
that most monitors will not display these values properly, so going by
the numbers using colour sampling is often necessary.

What made you start using ProPhotoRGB several years ago? I heard of it
only last week. I don't remember any of my Photoshop books mentioning it.
Looks like it would absolutely require 16-bit per-channel color support.
It was developed by Kodak. Here's a short introduction to it:

http://www.naturephotographers.net/articles1203/mh1203-1.html

Dark hues and shadow areas, eh. Thanks for the answers, Gordon!

 

[Gordon Moat]

What made you start using ProPhotoRGB several years ago? I heard of it
only last week. I don't remember any of my Photoshop books mentioning it.

There is a great deal of information that never makes it into PhotoShop books.
Also, PhotoShop is far from being the only answer in image editing, nor the best
answer, though it is now the most common software in usage. Recall that
PhotoShop is destructive image editing in most of the choices in that interface
and tools set.

I had a problem with out of gamut problems, or just missing colours on offset
prints. One thing that led to was a need for a larger colour space to retain as
much image information as possible. That search led to ProPhotoRGB, which is the
largest generally available colour space. I have to provide images in CMYK, and
using ProPhotoRGB allowed for a very close match, with little to no loss of
colour on most images. I should warn you that some non-PostScript printers
(desktop) prefer RGB information, and using ProPhotoRGB might be too large a
colour space, and not give the best results. Also, images going to newsprint
should use a much smaller colour space, with further limits adjusted on CMYK
output.

Looks like it would absolutely require 16-bit per-channel color support.

There is an older image editing and compositing software called LivePicture.
That allows for high bit manipulation in real time through a proprietary format.
It is easy to work with even 1 GB images on a computer made six years ago. This
software is similar to an earlier edition of Alias Studio, which use to be the
standard of image editing on Silicon Graphics computers. Unfortunately, the
company that produced LivePicture got bought out by another company, who then
decided to stop developing it, and also killed off all MacOS products. With
Alias Studio, the future development became Studio Paint, is still available,
though is very expensive.

I should mention that I rarely do any "adjustments" to images in 8 bit mode. In
fact, I do only a few adjustments in 16 bit mode in PhotoShop (or LivePicture)
to improve CMYK results. Unless I need to do a complex composite image, there is
little need to change to 8 bit mode, except as a final step to place images into
layout software (InDesign or Quark).

It was developed by Kodak. Here's a short introduction to it:

http://www.naturephotographers.net/articles1203/mh1203-1.html

Nice article. Very simple, and not very technical. Kodak does not explain
ProPhotoRGB very well, so for those more interested, that article is a good
starting point.

Dark hues and shadow areas, eh. Thanks for the answers, Gordon!

What the out of gamut warning is often telling you is that a printed image has
too much ink in those areas. The ideas are more discussed if you look into GCR
and UCR as they relate to printing. The basic idea is that the best papers
handle about 300% ink in any one spot (a few can do better, depending upon the
ink and press). So if you consider Cyan, Magenta, Yellow, and Black each at 100%
ink per plate, then that would give you 400%. Even if the RIP allowed placing
that much ink, the paper might buckle, or the ink might smear, or cause other
printed "distractions". So what a RIP tries to do is clip the total ink in any
one area below the limits of the paper and inks (newsprint is much lower than
300%). Almost none of this applies to inkjet printers, unless you have
PostScript colour management driving the printer.

Anyway, the basic idea is that going from RGB to CMYK, there are some colours
(or colour ranges) that do not translate well. Using a large space like
ProPhotoRGB can get you very close. You can always remove colour, but it is
tough to add colour. It has better uses in pre-press preparation than for home
enthusiast use.

As always, glad to be of help. Feel free to ask more questions.

Ciao!

Gordon Moat
A G Studio
<http://www.allgstudio.com/gallery.html> Updated!