[fpc-devel] Extract the color data and alpha from a PNG image

[Mattias Gaertner]

silvioprog <silvioprog at gmail.com> hat am 5. Februar 2013 um 16:08 geschrieben:

>  2013/2/5 Mattias Gaertner <nc-gaertnma at netcologne.de
> <mailto:nc-gaertnma at netcologne.de> >
>    > >    On Tue, 5 Feb 2013 12:37:24 -0200
> >    silvioprog < silvioprog at gmail.com <mailto:silvioprog at gmail.com> > wrote:
> >
> >    > Hello friends,
> >    >
> >    > I'm trying to extract the color data and alpha from a PNG image. In PHP
> >    > it
> >    > is very easy to implement, but in FPC I don't know how to do it. I
> >    > tried to
> >    > do it via "chunk.data", "ZData" etc., but, without success.
> >    >
> >    > Attached two files to test it. To test the PHP code run this command in
> >    > your terminal:
> >    >
> >    > php -f fpdf.php
> >    >
> >    > The in FPC code is partially complete.
> >    Have you tried fpimage?
> >
> >    uses
> >      fpreadpng, fpimage;
> >
> >    var
> >      image: TFPCustomImage;
> >      reader: TFPCustomImageReader;
> >      x,y: integer;
> >      c: TFPColor;
> >    begin
> >      Image := TFPMemoryImage.Create(0, 0);
> >      Reader := TFPReaderPNG.Create;
> >      Image.LoadFromFile(AFileName, Reader);
> >      for y:=0 to Image.Height-1 do
> >        for x:=0 to Image.Width-1 do begin
> >          c:=Image.Colors[x,y];
> >          writeln(c.Alpha,' ',c.Blue);
> >        end;
> >      //...
> >
> >    Mattias
> >  > 
>  Yes, I tried it too, but, without success. :(
> 
>  See my new code in attached. It generates the data, but with wrong content.

c.Alpha, c.Blue are word, not byte.

BTW, reading and writing to/from Filestream should be done in chunks, not in
bytes. That's dog slow.
Use a TMemoryStream as cache.

Mattias