[gs-devel] Getting a JPX stream's colorspace
ralph.giles at artifex.com
Thu Nov 29 14:48:25 PST 2007
On Fri, Nov 30, 2007 at 01:11:26AM +0300, Igor V. Melichev wrote:
> Well, now we have 3 spaces with no parameters (DeviceGray, DeviceRGB,
> and 2 with parameters : CIEBasedABC and ICCBased.
Indexed also has parameters.
> I think we must not assume that the PDF spec won't be improved with it.
> So lets keep in mind that Separation and DeviceN may be possible
> in future.
There's also the issue of transparency. The PDF spec currently leaves
this fairly unspecified, but I expect we'll see it at this point. I
understand the graphics library has support for images with a separate
transparency mask, but not direct RGBA-style image data?
> If it is restricted with a specific RGB, it can't be used generally.
> It could be used if it converts to as parameterized RGB,
> such as an ICC profile. Please explain more if you want me to think
> in this direction.
I don't know what you mean by "parameterized RGB". I think the spec
defines sRGB as a default so that "simple" image streams are in fact
calibrated, and not in some unspecified device space as in formats like
baseline JPEG. Because sRGB was designed to more-or-less match computer
displays (and now some computer displays are designed to more-or-less
match sRGB) this is a good default. For advanced use, one can specify an
explicit ICC profile.
> Besides all this, I suspect we'll get another problem
> with the PDF interpreter code. As you know, it is coded in Postscript,
> and expects a Postscript representation of a color space.
> Will need to shunt it with passing the color space data
> around Postscript (because a converting the C structure to Postscript
> looks too cumbersome). Possibly we'll need structure object
> to handle gs_color_space_s by iref, and to extend the PDF interpreter with
This Alex's domain, of course, but I was expecting to have to translate
whatever is returned into Postscript structures. If we do this, it
should be something we can reuse in porting the PDF interpreter to C.
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