gnuplot-info

[Gnuplot-info] Can't set background color in 4.2.5 on jpeg terminal

[rodgilchrist <rod...@ya...>]

The following script produces a plot with a black background and a red trace
on gnuplot 4.0.0, but produces a plot with a white background and red trace
on gnuplot 4.5.2.

One from a fresh install on OSX 10.5.7 via Fink. The other from a fresh
install via Macports. (As in both Fink and Macports were completely removed
and both port systems reinstalled from scratch.)

Is this a known bug or a known library configuration issue?

Thanks.

- Rod

gnuplot > file.jpg  <<XXX
set term jpeg size 1200,90 x000000 xffffff x0000ff xff0000
set datafile separator ","
plot [0.01: 3] 'file.csv' using 1:2 notitle  with lines
XXX

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Re: [Gnuplot-info] Can't set background color in 4.2.5 on jpeg terminal

[Thomas S. <t.s...@fz...>]

has something to do with the fact that the gd-library
sets the background to black for truecolor graphics.
this is repaired by gnuplot's gd terminal by drawing
a white background and then plotting over it.
but the old mechnism for non-truecolor graphics (1st
color is background color) doesn't work anymore.

you can see this when plotting a png-file with
set term png notrue
or
set term png true

BTW, using the jpeg terminal for plots with colored
background gives you a really poor plot quality, due
to the lossy compression algorithm, see 
http://www.nabble.com/file/p24117334/ts.jpg 
(this plot was done with a patched version of gnuplot)

it is better to use the png or gif terminal.


rodgilchrist wrote:
> 
> The following script produces a plot with a black background and a red
> trace on gnuplot 4.0.0, but produces a plot with a white background and
> red trace on gnuplot 4.5.2.
> 
> One from a fresh install on OSX 10.5.7 via Fink. The other from a fresh
> install via Macports. (As in both Fink and Macports were completely
> removed and both port systems reinstalled from scratch.)
> 
> Is this a known bug or a known library configuration issue?
> 
> Thanks.
> 
> - Rod
> 
> gnuplot > file.jpg  <<XXX
> set term jpeg size 1200,90 x000000 xffffff x0000ff xff0000
> set datafile separator ","
> plot [0.01: 3] 'file.csv' using 1:2 notitle  with lines
> XXX
> 
> 

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Re: [Gnuplot-info] Can't set background color in 4.2.5 on jpeg terminal

[rodgilchrist <rod...@ya...>]

Perfect Thomas, thank you. Both gif and png terminals work.
Also the jpeg comment is right on.

Can I suggest that this is a bug in the jpeg terminal that I believe could
be fixed by
changing line 1360 in gd.trm (PNG_graphics()) from:

        rgb = gdImageColorAllocate(png_state.image, 255, 255, 255);

to
        rgb = png_state.rgb_table[0];
        rgb = gdImageColorAllocate(png_state.image, (rgb >> 16) & 0xff, (rgb
>> 8) & 0xff, rgb & 0xff);

The 'terminal jpeg' statement is loading the background color entry. Might
as well just use it instead of a fixed white color.


- Rod



has something to do with the fact that the gd-library
sets the background to black for truecolor graphics.
this is repaired by gnuplot's gd terminal by drawing
a white background and then plotting over it.
but the old mechnism for non-truecolor graphics (1st
color is background color) doesn't work anymore.

-- 
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Re: [Gnuplot-info] Can't set background color in 4.2.5 on jpeg terminal

[Thomas S. <t.s...@fz...>]

i uploaded a patch on sourceforge yesterday which contains
your suggestion plus another correction (background color
of patterns):
http://sourceforge.net/tracker/?func=detail&aid=2809200&group_id=2055&atid=302055
(but for version 4.3 not for 4.2.x)


Perfect Thomas, thank you. Both gif and png terminals work.
Also the jpeg comment is right on.

Can I suggest that this is a bug in the jpeg terminal that I believe could
be fixed by
changing line 1360 in gd.trm (PNG_graphics()) from:

        rgb = gdImageColorAllocate(png_state.image, 255, 255, 255);

to
        rgb = png_state.rgb_table[0];
        rgb = gdImageColorAllocate(png_state.image, (rgb >> 16) & 0xff, (rgb
>> 8) & 0xff, rgb & 0xff);

The 'terminal jpeg' statement is loading the background color entry. Might
as well just use it instead of a fixed white color.


- Rod



Thomas Sefzick wrote:
> 
> has something to do with the fact that the gd-library
> sets the background to black for truecolor graphics.
> this is repaired by gnuplot's gd terminal by drawing
> a white background and then plotting over it.
> but the old mechnism for non-truecolor graphics (1st
> color is background color) doesn't work anymore.
> 
> 

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