Images in PDF -> JPG/BMP are they encoded differently?

Images in PDF -> JPG/BMP are they encoded differently?

Post by Dr Jool » Wed, 16 Jul 2003 21:21:16

Dear all, I am using PDEImageGetData and have found out that the pixel data
returned differs between different original picture format. I tried writing
the pixel data to jpg using jpeglib and I found that if the original image
came from a JPG, then it will write out to jpg ok, but if it was e.g. BMP,
it will not come out well even if it's also using DeviceRGB, 8 bits per
component, and same Filter. I don't see anything obvious between the JPG and
BMP... I thought PDF would decode all images into its own pixel array format
and it should make no difference whether it was originally a jpg or bmp or
whatever? Or am I wrong in thinking that? (I must be...)

Aandi said something before about BMP having GRB values rather than RGB or
something like that, so does it mean the pixel array is triplets of G R B
values? Wouldn't it be confusing, how do you know what to do with the pixel
data if you didn't produce the PDF yourself then? Any ways to find out its
colour depth (24bit, 32 bit etc) and its original format?

Please enlighten...

Cheers, Jules

***24 hours in a day...24 beers in a case...coincidence?***


Images in PDF -> JPG/BMP are they encoded differently?

Post by Carsten Neubau » Thu, 17 Jul 2003 18:23:13

hi jules,
you are right, JPEGs are inserted directly and BMPs are
transformed into some PDF-format.  
there's an official explanation to the PDF-format, named
"PDFReference.pdf", which tells you all about the details.
you can download it for free and google can tell you where.
carsten neubauer


1. PSD => BMP or JPG

Excuse me,
I've got a problem.
I bought my first scanner,and I use PhotoShop to edit the picture.
But, I  found that the size of the picture is too large, even if I use 100
DPI,100% settings.
Is there anyway to shrink the picture under 500 Kbytes?
How can I save the picture from .PSD file to .BMP file or .JPG file ?

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