Re: Color Conversions and Dither
Re: Color Conversions and Dither
- Subject: Re: Color Conversions and Dither
- From: Graeme Gill <email@hidden>
- Date: Fri, 16 May 2008 10:07:48 +1000
Fleisher, Ken wrote:
So the question is do you think it¹s better to apply multiple dithers or to
allow quantization errors in the early steps followed by dither in the last
step?
If you have a high bit depth workflow, then of course you probably
want to avoid dither until it is needed or desired. But an interesting
aspect is that very low noise images (CGI generated for instance) are
extremely susceptible to quantization artifacts, whereas images with
noise in them due to real world texture, film grain, sensor noise
or dither are a lot less susceptible to quantization artifacts.
(A subtle side effect of JPEG compression is that it tends to reduce
noise in high frequency components, making the decompressed images
more susceptible in subsequent quantization than non-JPEG encoded
images.)
So I would guess that if your 16 bit images have rather low noise levels
at the end of your processing chain, and you judiciously introduce
a minimal level of noise by the use of dithering (or even Photoshop
"Add Noise") of a magnitude of about the 8 bit quantizing step size (e.g.
around 0.5% or so), then the resulting images will be more visually robust
in the face of any subsequent quantization due to color conversion or
screening.
Graeme Gill.
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