Re: [Plplot-general] PNGs are fully transparent (i.e. no image)

[Andrew R. <and...@us...>]

Torquil,

There are some limitations with the gd driver support for transparency.
One of those is that 8-bit doesn't work well. It is generally best to
stick to 24-bit truecolor. Having said that, this sounds like it might
be a bug to me. I will try to investigate further.

Andrew

On Tue, Feb 05, 2008 at 09:08:24PM +0100, Torquil Macdonald S?rensen wrote:
> Hello, I had this working before but for some reason I now get fully 
> transparent PNG files, i.e. with no images in them, for all _except_ the first 
> PNG file I generate. E.g. the program below makes a good 1.png, but 
> 2.png is just transparent (pnginfo says all the colours used in it are 
> transparent). I know this because if I use "optimise", it says e.g. "2 
> colours, 2 transparent". Everything works fine when not using the 8bit 
> option.
> 
> Best regards,
> Torquil S?rensen
> 
> ********* "pnginfo" has the following to say about 1.png and 2.png: ***
> 
> 1.png...
>   Image Width: 800 Image Length: 600
>   Bitdepth (Bits/Sample): 8
>   Channels (Samples/Pixel): 1
>   Pixel depth (Pixel Depth): 8
>   Colour Type (Photometric Interpretation): PALETTED COLOUR (256 colours, 0 
> transparent)
>   Image filter: Single row per byte filter
>   Interlacing: No interlacing
>   Compression Scheme: Deflate method 8, 32k window
>   Resolution: 0, 0 (unit unknown)
>   FillOrder: msb-to-lsb
>   Byte Order: Network (Big Endian)
>   Number of text strings: 0 of 0
>   Offsets: 0, 0
> 
> 2.png...
>   Image Width: 800 Image Length: 600
>   Bitdepth (Bits/Sample): 8
>   Channels (Samples/Pixel): 1
>   Pixel depth (Pixel Depth): 8
>   Colour Type (Photometric Interpretation): PALETTED COLOUR with alpha (256 
> colours, 144 transparent)
>   Image filter: Single row per byte filter
>   Interlacing: No interlacing
>   Compression Scheme: Deflate method 8, 32k window
>   Resolution: 0, 0 (unit unknown)
>   FillOrder: msb-to-lsb
>   Byte Order: Network (Big Endian)
>   Number of text strings: 0 of 0
>   Offsets: 0, 0
> 
> ****************** Here is the program: ********************
> 
> #include <plplot/plplot.h>
> using namespace std;
> 
> int main()
> {
> plsdev("xwin"); // Screen plot
> plinit();
> plenv(0, 1, 0, 1, 1, -2);
> 
> plsstrm(1); plsdev("png"); // PNG plot
> plsfam(1,0,1); plsfnam("%n.png");
> plsetopt("drvopt", "8bit");
> plinit();
> plenv(0, 1, 0, 1, 1, -2);
> 
> double x[] = {0.0, 1.0}, y[] = {0.0, 0.5};
> 
> plsstrm(0);
> plbop(); plline(2, x, y); pleop();
> 	
> plsstrm(1); plcpstrm(0, 1);
> plbop(); plreplot(); pleop();
> 
> plsstrm(0);
> plbop(); plline(2, y, x); pleop();
> 
> plsstrm(1); plcpstrm(0, 1);
> plbop(); plreplot(); pleop();
> 
> plend();
> return(0);
> }
> 
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