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Date Posted: 10:23:20 10/25/03 Sat
Author: LoST
Subject: Detecting PNG Transparency and Progressive

Hi,

I want to write a simple program that decompress PNG files, but keep all other properties (transparency and progressive_mode). Here is what i wrote :

/**********************************************************/

PNGSource := TPNGGraphic.Create;
PNGSource.LoadFromFile(Fp);

if PNGSource.Transparent then PNGSource.SaveTransparent:=True;
Else PNGSource.SaveTransparent:=False;

PNGSource.SaveProgressive:=False;
PNGSource.CompressionLevel:=pcLow;
PNGSource.SaveToFile(Fp);
PNGSource.Free;

/**********************************************************/

Problems are :

1/ PNGSource.Transparency is always False (even with a png file that shows transparency in paint shop pro)

2/ I can't know if the original png file was saved using progressive mode or not

3/ You can add a pcNone in the TPngCompressionLevel that sets zlib compression to None :)

If one of you can help, thanks in advance !

LoST

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