Mike Chaney's Tech Corner

I ran into an something I did not expect yesterday with some test prints which were to compare prints on a new Epson 9900 of images in SRGB workspace and ProPhotoRGB workspace.
The same image was saved as tif files in a ProPhoto workspace and SRGB workspace. It had a blue (0,0,140) background.
The two images appeared identical in the Qimage preview screen, but the prophoto print background was almost black

It should be possible for others to reproduce what I saw if you have Photoshop and the 7xxx or 9xxx or any Ultrachrome ink profile
1. In photoshop create a solid colour layer of R 0 G 0 B 140 in the ProphotoRGB workspace.
    New, then specify ProphotoRGB in the advanced part of the the dialog box
    Then new solid colour layer using 0,0,140
2. In the view/proof setup, choose the Epson 9900 Premium Lustre 260 profile.

Repeat 1 and 2 after converting to SRGB.

The soft proof view matches exactly what the printer printed - very dark blue, almost black with Prophoto, and a rich blue with the SRGB workspace.

Also if you cycle through the profiles in Proof Setup with the Prophoto workspace, you see a huge variation in the Soft Proof view. Epson Luster profiles mostly give an almost black view and other profiles give closer to the shade I see on my monitor (98% Adobe RGB)

It's a curiosity, rather than a problem, but my conceptual model of the ProPhoto workspace needs some adjustment to explain what I am seeing. With what I understand about wide gamut workspaces, I did not expect this result.

Jim Swift

Hi Oston,

Maybe you expected too much  ;). Some colours in pro photo are outside the boundaries of human vision, never mind a smaller printer gamut. I expect, if everything else is set correctly, it is a question of rendering intent - try different ones wrt the printer (or display).

A useful link - http://www.photoshopforphotographers.com/pscs4/downloads/PSCS4-colormanage.pdf  - page 34 gives another clue.

Best wishes,

Ray

Thanks, Ray. I do know that pdf, having used it on a number of occasions. 

This is not a big problem for me. I was just taken aback by the magnitude of the difference. I posted this because seeing this result forced me to take another look at my own understanding of color spaces. I see now that it IS a gamut issue - and my not thinking that (0,0,140) could be out of gamut.

This example has been most useful  deepening my understanding. I think the  most instructive test for me came after posting the message, when I made a 16-bit gradient (0,0,0) - (0,0,255) in Photoshop and then examined the Out-of-gamut view with different printer profiles. I would guess that many people would be surprised by what they saw in such an experiment.

Thanks again for the reminder about the color management pdf.

Jim

Hi Oston,

I tend to do my editing using pro-photo colour space. Luckily I've not had a problem so far with oo gamut wrt printing - but plenty of others  ;) The link I mentioned, found as a result of your question, is not too bad a description of what is going on. I was not aware of the lower value for gamma in prophoto. There's just too much to think about :(

Glad you sorted it,

Best wishes,

Ray

Yes, I've also never run into any problems like this with normal camera-captured images and I also typically use ProPhoto in NX2 for those images.
 But the image that triggered this experiment had a (0,0,140) background created in Photoshop.

I have since reproduced the same results using other Ultrachrome Ink profiles. (0,0,140) in the ProPhoto workspace is out of gamut for the Ultrachrome inks, and
with some variations for the paper used, you need to do down to about (0,0,30) to get a shade (the very deep blue that I saw) that is in gamut.

It would be very helpful to hear from others who have done this test, to hear other peoples (esp Mike's :-)) ) explanations of what they are seeing. 

Thanks, Ray.

Jim

It's out of gamut!
See attached screen shot of a Gamut viewer with the point plotted (diamond shape) on it. The profile shown is for Ilford Smooth Gloss on an R800 with Epson Ultrachrome inks.
You get similar results for sRGB and Adobe RGB. RGB 0,0,140 is outside of all those gamuts.  :o
Terry.

Thanks very much for that confirmation, Terry.
I've been looking for a program like Gamut Viewer because the one I used ot use Microsoft Color Control Applet only runs on XP, not Windows 7 apparently. I'll take a look at that program.

Many thanks

Jim

Hi Terry,

Handy that the software will show a a value, as well as the profile.

Another visualisation method, since Jim uses photoshop, which will indicate gamut out of range errors, is given at http://www.fho-emden.de/~hoffmann/hungams17042004.pdf  with a simpler chart at http://www.curvemeister.com/tutorials/gamutviewer/index.htm

Best wishes,

Ray

I originally told the forum about it here:
http://ddisoftware.com/tech/computer-software/colour-gamut-visualisation/msg152/#msg152
However, it's not possible to get to that web site now. There are some older versions around I think (Google "Perfx gamut viewer").
If anyone would like a copy of v1.9, PM me with your e-mail address and I'll send the file.
Terry

That seems a really interesting program, Terry. But it only runs on the MAC!
Another program I found is http://gamutvision.com/docs/gamutvision.html. I'm not ready to plonk $99 for this kind of thing, but you can use it 20 times for free.

Jim

Me, a MAC user  :o  ???
I have do a Windows version. The link to the download on www.tglc.com is now dead and it seems you only get it when you buy some of their other software.
If you would like it, PM me.
Terry

Terry,
PM stands for Personal Message.
Is PMS the plural?
Fred

No. Why, have you got it  ;D
Terry.