[GRASSLIST:2270] Poor quality PNG file driver output

[Jason Horn]

Hi all,

I'm having trouble outputting images from the PNG file driver - the 
quality of the resulting .png images is very poor.  I put together the 
maps that I want to output using:

d.mon start=PNG
d.mon select=PNG
d.rast dem.relshade
d.mon stop=PNG

This does NOT give me what I'd see in the grass monitor if I'd used 
d.mon start=x0 instead of the PNG driver.  The colors in the image are 
interpolated, not enough shades of grey, for instance, as if the color 
palette was very small.  Lots of blotchy colors, and no smooth 
transitions and  gradients.

Markus, in your book you make the following reference on p. 187 in the 
section 8.1.3 on "Monitor output to PNG and HTML files"

"If the Gd2.x library is installed the driver supports true color 
output"

Because my images look like they don't have enough colors, I assumed 
this was the problem.  So, I installed the gd  2.0.9 library and tested 
it to make sure it was working.  I get the same poor quality images.  I 
AM setting the GRASS_TRUECOLOR=TRUE environment variable.

What's going on here?  Why is the output from PNG file driver so 
different from the output from the GRASS monitor?


Thanks in advance for any help.

Jason


Jason Horn
Boston University Department of Biology
5 Cumington Street  Boston, MA 02891

jhorn at bu.edu
617 353 6975