Re: Who"s right?
Re: Who"s right?
- Subject: Re: Who"s right?
- From: Graeme Gill <email@hidden>
- Date: Tue, 08 Jun 2004 11:25:16 +1000
- Organization: Color Technology Solutions
lagado wrote:
Am I mistaken or did you just answer my question posted as Mapping black &
white June 3. Do I understand you to be saying if a profile has been properly
gamut mapped, L*0 is automatically converted to the maximum shadow point of
the device, independent of the necessity for any other compression or
compensation algorithm?
I can't say, as it depends on the details of the source profile, destination
profile, the particular gamut mapping algorithm, and the intent of the user.
For perceptual rendering though, it might be generally regarded as a good thing
if the lightness axis of two colorspace are first brought into accordance.
And, wouldn't this, in theory at least, preclude
the necessity for any end point targeting?
I don't really know what you mean by "end point targeting". If you mean
adjusting a scanned/photographed image so that its black is black, and
its white is white, then no, they are rather different things, since the first
involves two colorspaces, and the second is image specific, within a single
colorspace (although the algorithms used might be rather similar).
Personally, my testing shows BPC to be redundant when used with perceptual
rendering.
If you're using conventional ICC tools, then I'd guess this is more by
luck than anything else. The whole point about BPC is that it takes the
specific black points of the actual source and destination colorspaces
into account, whereas the gamut mapping incorporated in the B2A table of
a destination profile, can't actually know what the source black point is
(although the operation of perceptual intent is subject to some debate
as to how it should operate at all. Should the perceptual A2B table expand the
luminance range to the PCS min and max ? Should the perceptual B2A table
assume that the source luminance range is the PCS min and max ? How do
matrix/shaper profiles that don't support intents fit into this ? The ICC
specification is difficult to interpret on these sorts of issues, and
interoperability between different profiles & CMMs is therefore uncertain).
Graeme Gill.
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