Re: epson 2200 > blackpoint compensation
Re: epson 2200 > blackpoint compensation
- Subject: Re: epson 2200 > blackpoint compensation
- From: Graeme Gill <email@hidden>
- Date: Wed, 17 Dec 2003 23:27:46 +1100
Roger Breton wrote:
Graeme Gill wrote:
A real gamut mapping process will map the luminance range (including
white and black) appropriately for the chosen intent.
You mean map ReferenceRGB 255,255,255 to DeviceCMYK 0,0,0,0 for the white
point "luminance" and ReferenceRGB 0,0,0 to DeviceCMYK c75, m68, y67, k90
(MaxTIL300% for US WebCoated SWOP v2) for the black point "luminance"?
No. I meant what I said. Mapping appropriately depends on the
characteristics of the two devices, the intent desired, and the
choice of mapping algorithm aimed at achieving the desired result.
For instance, the gray axis mapping function in Argyll, has 6
parameters that control how this mapping is achieved. Parameter
settings are the way an intent is implemented. The additional
factors fed into the mapping are the white and black points of
the source and destination gamuts, as well as the input image
white and black points (the latter being identical to
the source gamut white and black points if there is no separate
image gamut).
How would knowledge of the source gamut influence this conversion
differently?
By establishing the extremes that are to mapped. Of course this is
no great trick, nor is BPC. The point is that BPC is a very simple
version of what correct gamut mapping does. Given the full knowledge
of the source and destination gamuts, construct a mapping from one
to the other, that achieves the best possible result, guided by
the chosen intent.
Graeme Gill.
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