HSV decompose

[dinasset]

GIMP Version: 2.10.18
Operating System: Windows
GIMP Experience: Intermediate Level

List any relevant plug-ins or scripts:
(my Gimp comes from Samj's package)
decompose HSV
recompose

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This is to inform interested gimpers that it seems (but it could be I do not understand properly the function) that applying:
- decompose HSV
followed by
-recompose
the result is very strange

Here the original:

fiore-rosa-2_ORIGINAL.jpg (132.24 KiB) Viewed 2596 times

Here after decompose HSV then recompose

fiore-rosa-2_after-decomposeHSV-recompose.jpg (176.95 KiB) Viewed 2596 times

[Wallace]

Have you tried it on different images and sizes of images?

[dinasset]

Good idea, Wallace.
Tried on another flower image and it works properly.
What could be the problem in the source image?
Coul you try on my first image to see whether it happens also in your PC/Gimp environment?

[dinasset]

Additional info:
using my first image (the one which has a wrong behaviour in HSV), when choosing either decompoce RGB or decompose HSL, the recompose works fine.

[ofnuts]

Same on my 2.10.14 et 2.10.19 freshly compiled from the official GIT source. Doesn't happen if the image is converted to 32-bit FP.

[dinasset]

Thanks Ofnuts. I'm not alone.

[ofnuts]

Issue submitted: https://gitlab.gnome.org/GNOME/gimp/-/issues/5097

Seems to be a problem with hue values=255.

[rich2005]

Comparisons:

Works as expected in kubuntu 18.04 and regular (as-in from PPA) Gimp 2.10.14 and latest (14 may) Gimp 2.10.19 appimage.

Gives the fault in kubuntu (VM) 20.04 regular Gimp 2.10.18 (as-in from repo), a 2.10.18 snap version and exactly the same (14 May) 2.10.19 appimage as before.

not even going to hazard a guess

[ofnuts]

Comparisons:

Works as expected in kubuntu 18.04 and regular (as-in from PPA) Gimp 2.10.14 and latest (14 may) Gimp 2.10.19 appimage.

Gives the fault in kubuntu (VM) 20.04 regular Gimp 2.10.18 (as-in from repo), a 2.10.18 snap version and exactly the same (14 May) 2.10.19 appimage as before.

not even going to hazard a guess

Weird. I see the problem on my 2.10.14, I saw it in a self-compiled 2.10.18, and still see it in the self-compiled 2.10.19 with all latest updated. Are you using the same settings all over? If the image is converted to 32-bit FP the problem disappears.

[rich2005]

Default settings for everything.

Again in kubuntu 20.04 and Gimp 2.10.18 That 32 bit FP works but so does 8 bit linear rather than 8 bit sRGB.

The devs have been fixing the broken CMYK decompose might be a consequence of that. Is it the libbabl package to blame? in 18.04 / 20.04 the packages are 1.72 / 1.74

[ofnuts]

Fixed: https://gitlab.gnome.org/GNOME/babl/-/issues/54

However, better be in high-precision mode for this kind of thing, Decompose/Recompose doesn't recreate the very same image, some RGB values get shifted a bit in the process.

[dinasset]

Thanks a lot !