gimp 2.10.32 rgb / cmyk

[SKILKINKS35]

(07-14-2022, 02:50 PM)rich2005 Wrote:

Quote:If I leave the GRAY window at the bottom on "Select" the image can't get dowloaded into CYAN as a message tells you:   "Please set the default color profiles before loading images"

It is for when you have a greyscale image. Just set it to ISO Coated.

THANK YOU.

I have just done a test of converting the same RGB image into CMYK with GIMP/CYAN and the other with RGB2CMYK.ORG.

The latter seems darker with more contrast than the gimp:cyan one.

I was trying to send you the 2 photos but I couldn't since they had too many Mos!

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(07-14-2022, 02:50 PM)rich2005 Wrote:

Quote:If I leave the GRAY window at the bottom on "Select" the image can't get dowloaded into CYAN as a message tells you:   "Please set the default color profiles before loading images"

It is for when you have a greyscale image. Just set it to ISO Coated.

"I do not know which is correct but the web is outnumbered 3:1"

What do you mean by this?

Thank you

[rich2005]

Quote:"I do not know which is correct but the web is outnumbered 3:1"

What do you mean by this?

Well...if you look at the comparison images I made. https://i.imgur.com/71r76kD.jpg

The top one is the rgb2cmyk.org conversion
The next three are conversions using Cyan / Krita / PhotoShop These three largely match. So which is correct and which is wrong ? Consensus says the rgb2cmyk.org is wrong. But if you prefer the darker version, then yes, you will have to adjust your original image if you want to use Cyan.

[SKILKINKS35]

(07-14-2022, 03:33 PM)rich2005 Wrote:

Quote:"I do not know which is correct but the web is outnumbered 3:1"

What do you mean by this?

Well...if you look at the comparison images I made. https://i.imgur.com/71r76kD.jpg

The top one is the rgb2cmyk.org conversion
The next three are conversions using Cyan / Krita / PhotoShop These three largely match. So which is correct and which is wrong ? Consensus says the rgb2cmyk.org is wrong.  But if you prefer the darker version, then yes, you will have to adjust your original image if you want to use Cyan.

Thank you for the tests which are the proof in the pudding!!! The yellow of the girl's shirt in the CYAN and PHOTOSHOP conversion are very simiilar.
The KRITA conversion comes 3rd because the the yellow shirt seems paler. As for the RGB2CMYK, it just looks "dead"!

To tell you the truth, I have already done one book in sepia photos using rgb2cmyk.org (because i didn't know where to turn to and because rgb2cmyk.org was the only free (well, not so free...) online software I could find.
I'll let you guess the amount of testing I have had to do with the printer to get rid of that "darkness" within the photos...

By experience with rgb2cmyk.org, I had to avoid putting "contrast" to my photos and also have them a little "light/over exposed" to get near enough what I wanted.
Anyway, the 3 Cyan / Krita / PhotoShop conversions images you sent me definitely prove their point to me! It's the only way to compare.

It's just that from now on, if I'm going to use CYAN I'm going to take a different RGB grading approach in order to get what I think it's right for me (as it's all subjective, really) in the CMYK conversion.
I just will have to practice for, as you know, working on your own computer screen is one thing but confronting it the RGB result with the printers own screen and printing machine is another...

The only thing I have left to do is to download that software to check whether my photos are indeed in CMYK. I hope it won't be too complex...

In any case, Thank you again for your patience and your technological knowledge. Brillant!

[SKILKINKS35]

(07-14-2022, 02:50 PM)rich2005 Wrote:

Quote:If I leave the GRAY window at the bottom on "Select" the image can't get dowloaded into CYAN as a message tells you:   "Please set the default color profiles before loading images"

It is for when you have a greyscale image. Just set it to ISO Coated.

Thank you for your reply. This CYAN plug-in for GIMP is of a great help.

I have another question you maybe able to answer.

When I use the "perform shadows and highlights corrector" to "darken" a over-exposed sky behind an object I always get a white halo following the outside edge of the object.
The same effect in reverse actually applies if I want to "highlight" the object, it creates a dark halo following the inside edge of the object

Is there a way to avoid these 2 negative effects?

Thank you

[rich2005]

Looking back over the posts, this is before any RGB to CMYK conversion. Is that correct ?

The GEGL Colors -> Shadow-Highlights filter is not really one I use. Are you applying this to a selection ? (sky or foreground selected) I think it is more an over-all filter, although I can see a sort of halo effect.

A better bet might be using luminosity masks. The original plugin is a bit flakey in Gimp 2.10 but Ofnuts has a good version: see: https://www.gimp-forum.net/Thread-ofn-luminosity-masks and check out the link to the basics by Pat David.

A bit restricted by imgur file size but this a quick animation, using Ofnuts plugin. https://i.imgur.com/X8YCPev.mp4 Using a mid-dark (DD) for the foreground, the sky would be one of the 'L's.

[SKILKINKS35]

[attachment=8453][attachment=8453][attachment=8453]

Yes, this is before converting the RGB to CMYK conversion.
The shadow-highlights effect is applied to the whole image.

Are those "luminosity-masks" provided by Pat David or by Imgur.com?

I have attached an image showing my problem when I use the "Shadow-highlights" device in GIMP:
1) A white halo appears on the outside edge of the cross.
2) Adark halo appears on the inside of the cross.

[rich2005]

Yes I can see the problem. The solution is do not use the GEGL Shadow-Highlights filter. Use something else.

Quote:Are those "luminosity-masks" provided by Pat David or by Imgur.com?

You must have missed Ofnuts "smart" link on https://www.gimp-forum.net/Thread-ofn-luminosity-masks In full the download is:
https://sourceforge.net/projects/gimp-to...p/download

Other tools to try for adjusting your image(s)
There is always the Gimp curve tool.
The gmic ( http://www.gmic.eu ) channel processing filter is a bit more complicated but has options for tonal ranges. The gmic Shadow-Highlight filters also give a 'glow' effect so avoid those.

[SKILKINKS35]

OK. Brilliant!
Thank you very much for all these infos and links.

[rich2005]

(08-08-2022, 04:24 PM)SKILKINKS35 Wrote: OK. Brilliant!
Thank you very much for all these infos and links.

You know if you post a full image, someone bound to give some advice.

OK, I made up an image with a Dark FG and a lighter blue  BG. 

   

For the GEGL Shadows-Highlights filter that 'Halo' effect seems controlled by the radius parameter. Try making 'radius' as small as posssible. 0.1

[SKILKINKS35]

(08-08-2022, 04:57 PM)rich2005 Wrote:

(08-08-2022, 04:24 PM)SKILKINKS35 Wrote: OK. Brilliant!
Thank you very much for all these infos and links.

You know if you post a full image, someone bound to give some advice.

OK, I made up an image with a Dark FG and a lighter blue  BG. 



For the GEGL Shadows-Highlights filter that 'Halo' effect seems controlled by the radius parameter. Try making 'radius' as small as posssible. 0.1

Ah! Why didn't I think of this???
It's looks quite efficient, really on the cross but on the mountain, except there's a cutting line appearing all around the rock.
Any way to get rid of this "cutting line"?

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...but on the mountain, except there's a cutting line appearing all around the rock.