[Gnuplot-info] png as a backgroung image

[Ethy H. B. <eth...@in...>]

Hi all

I am sploting some 3D data and trying to use a png file as a backgroung 
image (w/alpha channel). The image is a grayed black and white version of some colored drawing.

The problem is if I first splot the bg image and then the data, the image
is plotted as if it was not grayed. All gray tones are "converted" to
black (rgb=#000000) and the mess is obvious.

I used:
splot   './data.txt' using 2:3:4:5 with linespoints lc rgb variable lw 2 pt 6 ,\
        './some_file.png' binary filetype=png dy=0.00000485 \
         dx=0.00000565 origin=(-45.66515,-22.77950,-99) with rgbalpha

If I first plot the data point and then the image, it appear grayed as it
should be *BUT* it is overwriting/erasing some points/lines where they "coexist"
and this is not desirable.

I used:
splot	'./some_file.png' binary filetype=png dy=0.00000485 \
        dx=0.00000565 origin=(-45.66515,-22.77950,-99) with rgbalpha , \
	'./data.txt' using 2:3:4:5 with linespoints lc rgb variable lw 2 pt 6

How can I solve this? Is it possible to make the background image stay in the
background?

Note: zdata ranges from -89 to -30
Note 2: view is set to "0,0,1,1"

Gnuplot is  4.4 patchlevel 3 (Ubuntu 12.04)
Tried with 4.6.1 patchlevel 0 (downloaded and compiled) with same results.

Regards

Ethy