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8 total messages Started by Tim Scarborough Wed, 10 Jul 2002 20:27

#1544

Author: Tim Scarborough
Date: Wed, 10 Jul 2002 20:27

1 lines
1086 bytes

I've just started with postscript, and I need a little help.  We have files that contain CMYK image data in separate channels (all the C, then all the M, etc).  We would like to compress the separate channels using RunLengthDecode/Encode.  Can this be done using MultipleDataSources using postscript?  Can it be done at all?  Thank you very much for any help.

Re: Help with MultipleDataSources

#1545

Author: Aandi Inston
Date: Wed, 10 Jul 2002 21:36

3 lines
860 bytes

How (in outline) are the channels separated at the moment?

Aandi Inston

Re: Help with MultipleDataSources

#1546

Author: Marc Antoni Malagarriga i Picas
Date: Thu, 11 Jul 2002 11:19

9 lines
1038 bytes

Hi Tim, 

Read the Image Dictionaries details in the PostScript Language Reference Manual, section 4.10.5 

Hope this helps, 

( ][  MaRC anToni 
 
PostScript&PDF Tools Developers

Re: Help with MultipleDataSources

#1547

Author: Tim Scarborough
Date: Thu, 11 Jul 2002 12:03

1 lines
1122 bytes

Currently the channels are separated into C,Y,M, and K in a file.  Right now we dither the data and send it to the printer, but the images are pretty big and we want to try to increase the speed.  I was hoping the RunLengthDecode filter with separate channels would do this.  Is this true?

Re: Help with MultipleDataSources

#1548

Author: Aandi Inston
Date: Thu, 11 Jul 2002 12:22

15 lines
1440 bytes

Compression can increase speed. RunLength is often a pretty
ineffective compressiom, though - if the printer is level 3, the
FlateDecode filter is much better. The public domain zlib library can
be used to compress.

Still, I don't yet see how compression and MultipleDataSources
overlap.  What PostScript technique are you currently using to make
these separate image data sources into a single image?  It isn't
obvious how you are doing that, so I can't (yet) see how it could be
converted.

Or - do you mean that the data is currently interleaved by pixel or
row, and you want to separate it?

Aandi Inston

Re: Help with MultipleDataSources

#1549

Author: Tim Scarborough
Date: Thu, 11 Jul 2002 12:42

3 lines
1354 bytes

We use a C++ app to read the data from a file.  We use this to send the PostScript commands to the printer.  We combine the separate image data sources into a single image before we send it to the printer (level 3).  I don't use PostScript to do this.  We're PostScript rookies, so we simply use the image "command" and we send the binary data to the printer.   

I can send the data separated or interleaved.  We thought that maybe separating them into MultipleDataSources and compressing would give us the speed gains we are looking for.  Are we wrong?

Re: Help with MultipleDataSources

#1550

Author: Aandi Inston
Date: Thu, 11 Jul 2002 13:32

12 lines
1454 bytes

Ok, so the sources are currently interleaved.

My recommendation would be to keep them interleaved and compress. Not
with RunLength which (as you probably recognise) is useless for
interleaved samples, but all together with Flate.

There is no practical way to run with separate channels to be combined
in one image.  Level 3 has a ReusableStreamDecode filter, but even
with that you hit a brick wall with big images; the images all have to
be held in RAM and you may not have enough.

Aandi Inston

Re: Help with MultipleDataSources

#1551

Author: Tim Scarborough
Date: Thu, 11 Jul 2002 14:30

5 lines
859 bytes

Aandi, 

Thanks for the help!  I'll take a look at Flate.  Hopefully I can get this thing working. 

Tim Scarborough

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