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Probleme couleur export en jpeg

New Here ,
Mar 17, 2023 Mar 17, 2023

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Bonjour,

 

j'ai un problème de décalage de couleur lorsque je sauvegarde une image en jpeg.

 

Avant tout je précise que j'ai un écran qualibré et que je travaille avec des profils colorimétriques adaptés à mes besoins, le plus souvent sRGB. Mais il ne s'agit pas d'un problème de "perception" de la couleur. C'est un problème de variation de valeur numérique.

 

Par exemple si j'utilise la couleur faf7f7 (R 250, V 247, B247), je sauvegarde en jpeg qualité maximale. Mon fichier jpeg va afficher la couleur fbf7f8 (R251, V247, B 248).

 

Si je sauvegarde en png alors les couleurs sont justes et parfaites. Vous pouvez mesurer les variations sur les exemples joints.

 

Avec une sauvegarde Tiff sans compression les couleurs sont juste, avec une sauvegarde Tiff compression jpeg j'ai les même erreurs.

 

Je suis sur la version PS 24.2.1 et sur windows.

 

Merci pour vos explications et pistes de réflexion.

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Community Expert ,
Mar 17, 2023 Mar 17, 2023

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jpg (at least what we mean by jpg in general) employs lossy compression. 

If you cannot tolerate the changes this causes then you should stick with lossless compression. 

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New Here ,
Mar 17, 2023 Mar 17, 2023

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Ok Thank you for this précision. That's mean with the best quality jpeg, and the lossless compression (value 12 on the option jpeg window) I have little changes to (like my exemple). If I want something perfect I must not use jpeg.

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Community Expert ,
Mar 17, 2023 Mar 17, 2023

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Value 12 is not lossless, it is still jpg after all. 

If you want complete reliability and unchangability lossy compression is not for you. 

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Community Expert ,
Mar 17, 2023 Mar 17, 2023

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@SanglierBlanc  If I want something perfect I must not use jpeg.

Jpeg files have compression applied, changing resolution or cropping enhances the compression artefacts - this means that Jpeg is only really suitable for final file delivery/transfer - once size and resolution (and any sharpening) have been completed.  Jpeg is not OK for archiving or for any file that may need to be resized or cropped down the line. 

 

I hope this helps
neil barstow, colourmanagement net - adobe forum volunteer - co-author: 'getting colour right'
google me "neil barstow colourmanagement" for lots of free articles on colour management

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Community Expert ,
Mar 17, 2023 Mar 17, 2023

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Years and years ago some people claimed that jpg at top quality would not damage an image – that was nonsense then and it still is. 

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Community Expert ,
Mar 17, 2023 Mar 17, 2023

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The root of that misunderstanding is probably that quality 12 is often referred to as "maximum quality".

 

In reality of course, there is no such thing as maximum quality with jpeg and it shouldn't be called that. The scale goes from high to low compression, but that compression is always destructive, non-reversible and cumulative.

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