<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN" "http://www.w3.org/TR/REC-html40/strict.dtd"> <html><head><meta name="qrichtext" content="1" /><style type="text/css"> p, li { white-space: pre-wrap; } </style></head><body style=" font-family:'DejaVu Sans'; font-size:12pt; font-weight:400; font-style:normal;"> On Monday, February 21, 2011 11:13:22 AM Alastair M. Robinson wrote: > Hi :) > > On 21/02/11 18:07, Hal V. Engel wrote: > > I can't find anything in either the autotools or cmake build systems for > > poppler that appear to turn CM for CMYK on or off. CM is either on or > > off and it does not appear to have any way to only turn it on for subset > > of object types or for specific output types. > > Well the default backend for poppler is Cairo, and Cairo (currently, as > far as I know) only supports RGB. Perhaps we'd need to use the other > backend, Splash, for CMYK support? configure --disable-cairo-output Might make CMYK output available? It definitly makes splash the default backend. For the cmake build it appears that WITH_Cairo=NO turns off cairo output. Using the splash backend needs to be tested to see if it will enable CMYK rendering. > > > But the way to get this tested is to start using it now so that issues > > can be ironed out as sooner. > > Yup > > > I don't think this will do too much for us if you are rendering > > everything to sRGB first and then to the final colorspace. > > I disagree - if you're rendering to sRGB as an intermediate step (which, > agreed, we don't really want to do - but it seems to be necessary for > CMYK output profiles at present) then using Relative Colorimetric when > rendering to the printer profile will result in black shades getting > crushed. > sRGB (normally, and in the case of the LCMS built-in sRGB which Poppler > uses) has a "perfect" blackpoint, with L* of 0, which no real-world > printer can achieve - so if you use relative colorimetric, any colours > darker than the blackpoint of the printer's profile will end up as black > as the printer can manage. > > For example - original image: > http://www.npandd.co.uk/coppermine/albums/userpics/10002/Bird.jpg > > Converted from sRGB to ISO Coated using Perceptual intent, then back to > sRGB (using rel-col+bpc to soft-proof). > > http://www.npandd.co.uk/coppermine/albums/userpics/10002/Bird_pc_p.jpg > > Finally converted from sRGB to ISO Coated using Relative Colorimetric, > then back to sRGB (again using rel-col+bpc for proof). > > http://www.npandd.co.uk/coppermine/albums/userpics/10002/Bird_rc_p.jpg > > Note how the rel-col version crushes the dark colours in the claws and > background. > > If we have to use sRGB (or some wider-gamut RGB space) as an > intermediate step, then we need to use Perceptual intent when converting > that to the printer profile. > > This isn't an issue when the printer's profile is RGB - poppler can > render directly to it - though my experiments last night suggest that's > not working properly either as yet. > > All the best > -- > Alastair M. Robinson </body></html>