Re: [APML] Reflecting on Cygnus

[Jerry Lodriguss <lists4@astropix.com>]

Hi Chuck,

Ok, you are using Photoshop CS2 with a Dell 2405FPW monitor that is 
calibrated with ColorSync and you say (not Monitor RGB), and Mac OS 10.4.1.

But you didn't say what you have the working color space set to in 
Photoshop. This is critical. Do you have the working color space set to 
something like Adobe, or do you have it set to the monitor profile created 
by ColorSync?




>And my point is it looks like he adjusted it to be viewed in sRGB. If
>viewed in a browser without that profile applied it may look far
>different. Here's what I see between the two:
>
>http://images.aa6g.org/RG_NGC6914NMM.jpg


Yes, there is quite a bit of difference you are seeing.  I don't see that 
much difference on my CRT or LCD.

But where did you do the screen captures?  Did you do the top one in 
Photoshop and the bottom one in a browser?  If so, which browser?  Or did 
you do the bottom one in Photoshop with ? what as the working color space?



>>A more valid test would be to set Photoshop's working color space
>>to the monitor profile, and then see what the image looks like with
>>and without the sRGB color tag applied. (Note that you should never
>>set Photoshop's working space to the monitor profile for real).
>
>Why? If you're only viewing on monitors what difference does it make?
>Or is it one of the standard working spaces is just to normalize
>between monitors?


Yes, that is the whole purpose of the standard working spaces. It gives you 
a device independent color space to edit in.

If you have Photoshop's working color space set to your monitor's profile 
(whether created in ColorSync or Adobe Gamma, or with a hardware device), 
you are essentially using Photoshop as it behaved prior to when they 
implemented color management (pre version 5 I think).

You do not want to edit in your monitor's color space. If you do, you will 
ensure that no two users see the color in the same way, because the numbers 
that describe the color are different on every output device. That's what 
color management and the working space do - they translate the *meaning* of 
the numbers between devices. The standard editing color spaces like Adobe 
are synthetic constructions, they are not based on actual input or output 
devices.

A monitor's color space is a bad place to edit because:

1. in the standard working color spaces such as Adobe,  equal values of red 
green and blue are neutral. This is not true of a monitor's color space.

2. standard working color spaces are linear, and a monitors color space 
isn't. Equal adjustments to different parts of the tonal range will yield 
different results.

3. If you work in your monitors color space as Photoshop's working color 
space, you may be throwing away some colors that are actually present in 
the original data but that cannot be displayed on your monitor, but may be 
able to be printed on, say, a Chromira or Lightjet.  Once you save the file 
in the monitors color space, you have permanently thrown these colors away. 
This is, of course, true for working in any smaller color space as your 
working color space, such as sRGB.



>The test is exactly valid for showing the difference being the
>profile applied and not applied when viewed in a given working space.



No, it's not.  That's not what you are doing.  You are actually showing the 
difference with the correct profile applied, and with an incorrect profile 
applied.

Your test completely depends on what you have set as the working space in 
Photoshop.

If you have Photoshop's working space set to sRGB, you won't see any 
difference at all.

If you have it set to any other color space other than sRGB, it is an 
invalid test because when you select "Don't manage color", you are actually 
assigning Photoshop's working color space to the image. THIS IS THE 
CRITICAL PART where you are going wrong.

Of course the brightness or color will look different. You are 
un-intentionally misusing the color management.

Furthermore, it is not fair, indeed, it doesn't even make sense, to compare 
what an image looks like with the correct color space tag applied, and then 
"not applied in a given working space".

If Rob's image had an sRGB color space tag applied, and you viewed it on a 
Mac with ColorSync correctly set up, and in a browser that supports color 
management, then it should look correct.

I don't know what the Mac's system level ColorSync default color space is. 
I should though, so I'll have to go look it up.

If you viewed it on a Windows machine, then sRGB is the default color space 
for the system level color managment, and it should look correct whether it 
is tagged with sRGB or not, since, in fact, it is in sRGB.



>It seems to me that the bottom line is don't do any color management
>if you know the images will be viewed mostly in browsers that don't
>manage color. Embedding profiles and then ignoring them is worse than
>ignoring profiles altogether. ;-)


Well, there is, obviously, a ton of confusion about this entire subject.  I 
don't think that not doing any color management at all is any better of a 
solution.  In fact, I don't think you can even "turn color management" off 
in Photoshop because the display is always going to be output through the 
monitor's profile.

If an ignorant user had his working color space set to, say, Adobe, or 
Wide-Gamut RGB, and he worked on his images in that color space, and then 
he didn't convert to sRGB before saving the jpeg for the web, or if he 
simply saved a file and didn't embed the correct color space tag, then the 
images would look bad, and they would be incorrectly displayed.

The bottom line is that most browser's do not support color management. So, 
if you convert your image to sRGB before you save it, and then save it with 
an sRGB color space tag, that is about the best you can do, as Rob has 
done. That way, if someone opens it in a correctly color managed 
application, such as Photoshop, and if they have the color settings set 
correctly, then it will display exactly correctly.  If they open it in a 
non-color managed browser on a Window's machine, it will display 
correctly.  If they open it on a browser on a Mac that doesn't support 
color management, then I don't know what it does.

I wonder if the brightness difference you are seeing is because you are 
working on a Mac and have the gamma set to 1.8 instead of 2.2?

Jerry



_______________________________________________
Astro-Photo mailing list
Astro-Photo@seds.org
http://seds.org/mailman/listinfo/astro-photo