Re: LAB as working/interchange space
Re: LAB as working/interchange space
- Subject: Re: LAB as working/interchange space
- From: Chris Cox <email@hidden>
- Date: Thu, 24 May 2001 11:02:41 -0700
At 12:49 AM -0600 5/24/01, Chris Murphy wrote:
Chris Cox writes:
16 million colors in 8 bit/channel sRGB will transform to only 2.47
million colors in 8 bit/channel LAB (without dithering).
and
But if you look into
the details at all, you quickly find that LAB is not a great
representation for your image data. It's a nice mathematical
construct for interchanging data -- but whenever you use LAB you have
to keep around extra bits of precision to maintain image quality.
Why is it that I can take a wide variety of RGB images defined with
Adobe RGB, convert them to Lab, then take the Lab set of images and the
RGB set of images - and convert them properly from their respective
source to a destination using a suitable output device profile - and end
up with visually the same thing? From inkjets to printing presses, I
don't see the decrease in image quality.
Usually, you won't see the effects, but sometimes you do.
And if you apply lots of adjustments, the quantization effects become
VERY noticable.
I have no doubt what you're saying is true, I'm just wondering to what
degree this actually affects the reproducibility of images? In what
respects should I be seeing image degradation just by converting a good
RGB image into 8-bit/channel Lab?
In PS6, turn off dithering in color preferences, and convert a high
quality 8bit RGB image to 8 bit CMYK, and convert the same source
from RGB to LAB to CMYK. Now compare the 2 CMYK results -- the one
that stopped in LAB will have more banding because of the
quantization in LAB. The directly converted image will have less
banding because it kept around a lot more bits when converting in and
out of LAB.
Chris