Comments on: Episode 033: The Channel Mixer – Monochrome conversion (2)

By: Rolf

Rolf — Sun, 19 Jul 2009 12:50:43 +0000

Norman, going to this modern stuff with emulsions was a big mistake.

We should have stayed with the big invention of M. Daguerre. So much detail is lost with these modern techniques!

On the other hand I am really not sure if we should have started with this picture stuff 50000 years ago. Decorating walls of caves with animals – what a waste of time!

(I had once a chance to look at a Daguerreotype with a microscope – the detail is indeed incredible – better than any film or sensor. But there are other drawbacks – including a nasty and early death by mercury poisoning. )

By: Norman

Norman — Sun, 19 Jul 2009 12:15:21 +0000

There is no such thing as “The perfect monochrome image” and monochrome images are not necessarily black and white. Surely, a negative image produced by chemically processing the latent image stored in an emulsion containing minute particles of silver halide, layered onto a transparent substrate will have a vast range of grey from black to white. The content of this negative image will inevitably be changed when converting it to a positive image on paper and much of the detail will be lost. The impressive images that are published are inevitably the result of considerable work in the darkroom and the retouching studio.

So, Sergio, I challenge you to describe the process whereby the so called real BW negative is obtained and how it is converted into the so called perfect monochrome image.

By: Sergio

Sergio — Sat, 18 Jul 2009 23:38:37 +0000

The perfect monochrome image is, of course, derived from a real BW negative.

By: The p-Code Machine » Meet The GIMP

The p-Code Machine » Meet The GIMP — Sun, 14 Dec 2008 12:24:40 +0000

[...] Episode 033: Fade to grey, channel mixer, part 2 [...]

By: Meet the GIMP « Ang Pilipino GIMP

Meet the GIMP « Ang Pilipino GIMP — Wed, 05 Mar 2008 01:51:32 +0000

[...] Episode 033: The Channel Mixer – Monochrome conversion (2) [...]

By: Serge Gielkens

Serge Gielkens — Tue, 04 Mar 2008 17:22:29 +0000

@David.
Finally I had time to look at this. Up till now I used sRGB and Adobe RGB colour spaces. I did experiments with CIE D65 and sRGB working spaces following the examples of Eric Brasseur and that was an eye opener. I was never aware of this gamma error. I have to adjust my workflow.

Thanks!

By: Rolf

Rolf — Sat, 23 Feb 2008 11:08:35 +0000

David, that was great input. I have to tackle that field…..

By: jaims

jaims — Sat, 23 Feb 2008 08:48:52 +0000

By the way, I use a panasonic dmc-fz30, but I haven’t been able to find a icc profile file for it.
But ufraw is said to be able to manage this camera’ pictures. What does that mean? Using ufraw I can’t choose a different icc other that the built-in (sRGB)…

Is there a place in the inet where I could be looking for my camera icc file?

By: David gowers

David gowers — Fri, 22 Feb 2008 23:04:21 +0000

oh, and of course those things can be set up in the Preferences dialog, under ‘display’ (or is it ‘color management’/)

‘Assign profile’ and ‘Convert to profile’ can be found in the image->mode menu

You can toggle between a color-managed and non-color-managed display by bringing up the ‘view->Display filters’ dialog and toggling ‘color management’. This is not terribly useful except as a visual aid.

Image properties dialog includes a ‘color profile’ tab which can show you the description of the attached color profile.

By: David gowers

David gowers — Fri, 22 Feb 2008 22:57:30 +0000

Not me I’d like to be able to make videos, but my computer just slows down to unusability when I’m trying to.
It’s about as simple as I said, though.

Each image can have a ICC profile: this indicates the parameters of it’s colorspace (ie what does RGB 0 0 0 mean; what does RGB 45 100 64 mean, .. what does every possible value in the colorspace mean in objective terms.)

A display has a ICC profile: this indicates the parameters of it’s colorspace. If you have no display profile assigned, a builtin sRGB profile is used as the display profile. Before display, the image pixels are transformed from the image colorspace to the display colorspace.

sRGB is an acceptable default profile (actual displays vary — they tend to expect sRGB, most displays distort the output somewhat due to imperfections or user misadjustment)

Most programs, unfortunately, disregard ICC profiles (which can be embedded in PNGs, .. or XCFs of course:)
This is why it is necessary to transform back to sRGB before saving the image; otherwise, most programs just assume that your data is sRGB, so your results will not look as you intended.
See the second link I provided before — it gives an example of this.

This is changing though — eg. recent development versions of Firefox 3 have ICC support.

By: Rolf

Rolf — Fri, 22 Feb 2008 11:53:26 +0000

I have to confess that I have no real clue about this profile stuff. I know a bit, but not enough.

Is there anybody to make a video out of this?

By: jaims

jaims — Fri, 22 Feb 2008 07:34:24 +0000

Thanks for that info and links, David; all of it is sort of ‘never heard before’ stuff to me…

I think the article on the last link you provided (ericbrasseur) is a very good one.

And seems like photo edition is a very large topic, plenty of things to learn

By: David gowers

David gowers — Fri, 22 Feb 2008 02:39:33 +0000

you could also improve the quality of the grayscale conversion by making sure the picture is in linear RGB colorspace rather than sRGB. That is doable by:
1. get a linear RGB ICC profile (see http://www.aim-dtp.net/aim/techniques/linear_raw/index.htm — search ‘D65 Gamma’)
2. get an sRGB ICC profile (the one available at http://www.color.org/profiles.xalter is excellent)

3. set your display profile to the sRGB profile
4. (hopefully, if you think the benefits of linear working space are worth it) set your working space to the linear profile.
5. convert any sRGB images to linear upon loading (assign the sRGB profile if no profile was assigned, then convert to linear profile.)
6. convert linear RGB images to sRGB before saving a copy for print or display.

I realize that with the limited 8-bit image format of GIMP, some degradation may occur upon conversion. However I suspect the subsequent ease and quality of grayscale conversion, channel mixing, and other manipulations are worth it.
As ‘Meet the GIMP’ seems largely focused on photography, I’m surprised you haven’t covered working in a linear space already. Editing in sRGB can certainly cause some serious problems (-> http://www.4p8.com/eric.brasseur/gamma.html)

By: Rolf

Rolf — Thu, 21 Feb 2008 21:48:37 +0000

Everything is allowed – as long as it is (at least) partly made monochome.

By: jaims

jaims — Thu, 21 Feb 2008 21:15:36 +0000

I’m going to try to post-process a picture anyways, Serge, besides ‘monochromizing’ it… just to try to find funny results

By: Serge Gielkens

Serge Gielkens — Thu, 21 Feb 2008 20:46:43 +0000

Thanks for the link to Cambridge in Colour. Stunning pictures. I have to explore that site in more detail.

Good to see a challenge again. Do you only accept a conversion to B&W or is post-processing also allowed?

By: jaims

jaims — Thu, 21 Feb 2008 15:21:25 +0000

Nice stuff, and nice tutorials in Cambridge in colour