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September 2006
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2006.10.19 12:56 "Re: Status of ISO JBIG and CIELAB JPEG support", by Leridant Jean-yves
Joris a écrit : >Jean-Yves Le Ridant wrote: > > >>I agree and its for parts a result, when trying to add some general >>support for lab/jpeg/tiff files, of dealing with specs, some "state of >>art" of libtiff 3.7.3 ( don't know if things have changed ), tifftools >>( mainly tiffcp ), photoshop, and ... my own user's requests. >>;-) >> >> > >I think we've some communication problems going on... > Yes and no ! I didn't take anything in offense :-)) Just something like a "hard disk failure" on my main worstation added to parano network administration ..., and coming with Thunderbird Please, tell me what about this html <censored> for this list. Rather, I highly appreciate someone submit my files to his own "inspector". "Le diable habite les détails", especially when ... "enhancing" some small area of a so widely dispatched soft as libtiff, and some lack of feed back is one of the reason why this job is "suspended" since one year. >As far as this problem is concerned, the way my decoder handles this is >the following: > >- if colorspace is YCbCr > - if Subsampling tag is not present > -> assume TIFF 6.0 default [2,2] applies > - else > -> assume Subsampling tag is correct >- else if colorspace is CIE, ICC or ITU Lab > - if Subsampling tag is not present > -> assume writer thinks subsampling doesn't apply, i.e. assume >[1,1] > - else > -> assume writer thinks subsampling applies, i.e. that this tag >is correct >- else > -> assume no subsampling, regardless of tag presence > [...] >I've not yet made a definite choice in the encoder, though. So I for one >am hoping someone with authority tries to clean up this confusion in a >proper manner. (For example by allowing encoders to either disregard or >apply subsampling to CIE, ICC, and ITU Lab, at will, by making the >default for this tag be [1,1] as far as these Photometrics is concerned. >Messy to have the default depend on the value of another tag, but it may >very well be the only way out, and it certainly is consistent with the >files out there already.) > The above "policy" look very like where I came in my jobs, with some difference, there's no real "codec", and are handled by changes in libtiff ( not so much except tif_jpeg.c ) and tiffcp. This is a *bad thing*, resulting of historical reasons : I have been long to understand that no serious job could be done without exploring in depth some process involded around for example JPEG_COLOR_MODE pseudo tag ... ;-))) More, one of my major goal was to "way out horrible jpeg CIELAB files", so I used this pseudo tag to have a parallel relationship CIE/ICC as RGB/YCC defaut transformation. Then added a flag to "raw decompress" and it is "logic" : no color transform but no upsampling anymore ---> interleaved subsampled file as every one like them :-))) And ITU is proceeded at end exactely like YCC, except tags. This is approx "the state of my art". :-) Restarting this job ( has someone ITU lab files, is there some "authority" somewhere ?) I think all this policy could be handled by extendORing the JPEG_COLOR_MODE pseudo tag, with respect of "oldunaware" _RGB _RAW. It is not a tremendous job, as soon as some mechanism in the lowlevel part of tif_jpeg.c are reliable. It was not the case, in version 3.7.3 : I persist some of the problem of too many too few scanline, tiffcp crashes, ... are in tif_jpeg when leaving the usual sheme RGB --> YCC 2:2 ---> RGB Best regards -- Jean-Yves > > >