[SATLUG] nnOT: Graphics knowledge / preparing (TIFF) images for

Borries Demeler demeler at biochem.uthscsa.edu
Mon Aug 29 09:47:34 CDT 2011


> Questions:
> 1. Are PNGs used in print publications? Would quality degradation be
> apparent by simple graphs?

I submit png images to publishers all the time instead of much larger
TIFFs. Even though they don't officially list them as acceptable
formats I have never seen one reject a png.

> 2. I used imagemagick:
>  for i in *png; do convert $i -colorspace cmyk $(echo $i | sed -e
> 's/.png/.tif/g'); done
> to convert PNGs to TIFF files (with cmyk colorspace). When resized the
> print becomes unreadable. Why? How might this be avoided?

Not sure on this, but I would try to convert one image manually in gimp
to see if the same problem exists. There should never be any loss when 
converting between TIFF/png as long as the size is not changed. I wonder
if it is even necessary to specify the color space, this should be 
implicitely conserved.

> Wondering - The graphs should be 300 or 600dpi. The approximate image
> sizes for many are 1.87 x 2.89 inches. Should the images be generated as
> 1122 x 1734. This does not seem to help when rescaled to smaller images.

That would seem to be the right size for 600 DPI. The way I usually
generate publication quality graphs is to first output them as a 
scalable postscript image (not bitmap based) and then load the image
into gimp, manipulate whatever else it needs, and then save it as a PNG.
Scaling can be done as well. I have always gotten excellent results
without loss of quality when using pngs (except when downscaling of course).
JPGs do not work well in this respect, there is always loss of information
and artifactual pixellation.

> 3. R creates images in many formats. I used almost the identical command
> - basically only changing tiff for png - to create tiff graphs. The
> dimensions (though the same) aren't coming out right. (I don't know if
> this is an R issue or something I don't understand about graphics.)

This could be a printer driver issue. You don't want to change the
aspect ratio because it may make your fonts look funny, but instead you
could include some white space if the publisher is picky.

-b.


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