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Re: write JPEG

davidf@dfanning.com (David Fanning) wrote:

>It should have read something like this:
>  You can't specify the resolution when you write the file,
>  but you can specify the resolution of the image by
>  changing its size before you write to the file. 

Hm, actually this may not help. All that write_jped does
is to encode the bitmap and write it into the file. A JFIF
file has a header that contains the size of the picture 
when it will be printed by some other software.

If I cannot set the size of the encoded picture I will
need some more steps later to specify it. Even worse, 
some software will resample the bitmap before printing
and I have either supply parameters for this step or
- worse - I can't control it.

For a test I did  

  write_jpeg, "c:\temp\look.jpg", Bytscl(Dist(100))

and got a tiny file. Opening it with PaintShop Pro it tells
me the file has 72 DPI and a size of 100/72 inches.

Unfortunately there are more bitmap formats supported
by IDL that do not allow to pass the picture size for
printing. However, write_bmp does: Keyword header_define

It would be a great improvement to add this feature to
the other write_<your flavour> procedures.