Lab Colour Space versus AdobeRGB


Link Posted 08/11/2007 - 23:58
For some adaptations in Photoshop we have to change the modus from AdobeRGB tot Lab Colour Space. After the adaptations we have to switch back tot AdobeRGB. Does this have an influence on the quality of the picture?


Link Posted 09/11/2007 - 07:49
In theory yes, a small amount of error could creep in. In practice, providing it isn't done repeatedly, it isn't any detriment to the image.
Best regards, John


Link Posted 09/11/2007 - 09:04
I studied digital image processing as part of my degree, the maths involved in switching between colour spaces is shockingly complicated, and a certain amount of rounding errors will always turn up.

Treat it like saving to JPG, once is absolutely fine, a few times you can get away with if the quality is high, but it should be kept to a minimum where possible.
you don't have to be mad to post here

but it does help


Link Posted 09/11/2007 - 09:13
There will be some cases of rounding errors when converting. You can, as John rightly says, cut down the number of conversions to a minimum - then these errors will only be slight and generally not noticed. (If you want to test this, create a script that will convert back and forward between two colour modes, and run the script 100 times - you should start to see any errors by then!)

At least one retouch expert suggest copying the image to a new image, do the conversion, then paste the results as a new layer in the original image (this keeps the original untouched - which is important for retouch work).

(For gallery, tips and links)


Link Posted 09/11/2007 - 14:44
Thanks for the answers.
So the conclusions might be: we can convert from AdobeRGB to Lab Colour Spaceand back, but only once and only if necessary. The idea of doing it in a copy layer is always useful.


Link Posted 09/11/2007 - 14:58
Not sure you have to worry about it to that degree.
Most of the functionality in Photoshop is done behind the scenes in Lab mode. So conversions are likely being done anyway. (adjustment layers probably help minimize this a bit by performing a lot of the mods in an intelligent order... one would hope)

Although you probably don't want to do repetitive conversions for no reason, you're probably doing so to make changes to the image that will FAR outweigh any rounding errors that might be introduced from the Lab<->RGB conversion itself.

In general I wouldn't worry that much about it.
If you're doing a lot of mods, work in 16 bit mode. When you convert back to 8 bit for viewing/printing those rounding errors wont make a significant difference (unless your performing thousands of conversions)
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