delphi convert gif to png with transparency - delphi

Question

I am trying to convert a gif to png, that's easy, but the problem is the result image is not transparent, also I would like to have in the png image the alpha channel.
This is my code:
procedure TForm1.Button1Click(Sender: TObject);
var
png: TPngImage;
p : TPicture;
begin
p := TPicture.Create;
p.LoadFromFile('C:\temp\php.gif');
png := TPngImage.CreateBlank(COLOR_RGB , 8, p.Width, p.Height);
png.Canvas.Draw(0,0, p.Graphic);
png.SaveToFile('C:\Windows\Temp\test.png');
end;
The new picture has the background black, should be transparent.
If I try to add the ALPHA in the constructor, is 100% transparent.
png := TPngImage.CreateBlank(COLOR_RGBALPHA , 8, p.Width, p.Height);

Answer 1

Since Delphi XE 2 GDI+ is supported, which offers real easy to use options for conversions.
You just need to create TGPImage providing the image file to load and save this image with the wished encoder, found by the desired mime type.
uses Winapi.GDIPAPI, Winapi.GDIPOBJ, Winapi.GDIPUTIL;
procedure TForm8.Button1Click(Sender: TObject);
var
encoderClsid: TGUID;
stat: TStatus;
IMG: TGPImage;
begin
IMG := TGPImage.Create('C:\temp\transparent.gif');
try
GetEncoderClsid('image/png', encoderClsid);
stat := IMG.Save('C:\temp\transparent.png', encoderClsid, nil);
finally
IMG.Free;
end;
if (stat = Ok) then
Showmessage('Success');
end;
examples for the mime types:
image/bmp
image/jpeg
image/gif
image/tiff
image/png

Answer 2

Just by drawing GIF image on PNG canvas will not move transparency information from GIF image to PNG.
You will have to do it yourself.
ForceAlphaChannel procedure will create alpha channel for any PNG image based on given TransparentColor.
procedure ForceAlphaChannel(Image: TPngImage; BitTransparency: Boolean; TransparentColor: TColor; Amount: Byte);
var
Temp: TPngImage;
x, y: Integer;
Line: VCL.Imaging.PngImage.pByteArray;
PixColor: TColor;
begin
Temp := TPngImage.CreateBlank(COLOR_RGBALPHA, 8, Image.Width, Image.Height);
try
for y := 0 to Image.Height - 1 do
begin
Line := Temp.AlphaScanline[y];
for x := 0 to Image.Width - 1 do
begin
PixColor := Image.Pixels[x, y];
Temp.Pixels[x, y] := PixColor;
if BitTransparency and (PixColor = TransparentColor) then Line^[x] := 0
else Line^[x] := Amount;
end;
end;
Image.Assign(Temp);
finally
Temp.Free;
end;
end;
If you add call to ForceAlphaChannel after you have drawn GIF image you will get transparency based on transparent color you define.
procedure TForm1.Button1Click(Sender: TObject);
var
png: TPngImage;
p : TPicture;
TransparentColor: TColor;
begin
p := TPicture.Create;
p.LoadFromFile('C:\temp\php.gif');
TransparentColor := clFuchsia;
png := TPngImage.CreateBlank(COLOR_RGB , 8, p.Width, p.Height);
// set png background color to same color that will be used for setting transparency
png.Canvas.Brush.Color := TransparentColor;
png.Canvas.FillRect(rect(0, 0 , p.Width, p.Height));
png.Canvas.Draw(0, 0, p.Graphic);
ForceAlphaChannel(png, true, TransparentColor, 255);
png.SaveToFile('C:\Windows\Temp\test.png');
end;

Answer 3

For older/new Delphi versions (in newer version - change TPngObject to TPngImage).
If you need to save every frame of (animated) GIF into PNG (works for non-animated GIFS also):
The first variant code is compatible with the newer pngimage Version 1.56+ (which supports the CreateBlank constructor)
procedure TForm1.Button1Click(Sender: TObject);
var
Gif: TGifImage;
Png: TPngObject; // for new Delphi versions use "TPngImage"
Bmp: TBitmap;
TransparentColor, Pixel: TColor;
I, X, Y: Integer;
AlphaScanline: pByteArray;
IsTransparent: Boolean;
ColorType: Cardinal;
begin
Gif := TGifImage.Create;
try
Gif.LoadFromFile('C:\Downloads\ajax-loader.gif');
for I := 0 to Gif.Images.Count - 1 do
begin
IsTransparent := Gif.Images[I].Transparent;
TransparentColor := Gif.Images[I].GraphicControlExtension.TransparentColor;
Bmp := Gif.Images[I].Bitmap;
if IsTransparent then
ColorType := COLOR_RGBALPHA
else
ColorType := COLOR_RGB;
Png := TPngObject.CreateBlank(ColorType, 8, Bmp.Width, Bmp.Height); // for new Delphi versions use "TPngImage"
try
AlphaScanline := nil;
for Y := 0 to Bmp.Height - 1 do
begin
if IsTransparent then
AlphaScanline := Png.AlphaScanline[Y];
for X := 0 to Bmp.Width - 1 do
begin
Pixel := Bmp.Canvas.Pixels[X, Y];
Png.Pixels[X, Y] := Pixel;
if IsTransparent then
begin
if (Pixel = TransparentColor) then
AlphaScanline^[X] := 0
else
AlphaScanline^[X] := 255;
end;
end;
end;
Png.SaveToFile(Format('%d.png', [I]));
finally
Png.Free;
end;
end;
finally
Gif.Free;
end;
end;
For old pngimage version before 1.56 which do not support TPngObject.CreateBlank:
procedure TForm1.Button2Click(Sender: TObject);
var
Gif: TGifImage;
Png: TPngObject; // for new Delphi versions use "TPngImage"
Bmp: TBitmap;
TransparentColor, Pixel: TColor;
I, X, Y: Integer;
AlphaScanline: pByteArray;
IsTransparent: Boolean;
begin
Gif := TGifImage.Create;
try
Gif.LoadFromFile('C:\Downloads\ajax-loader.gif');
for I := 0 to Gif.Images.Count - 1 do
begin
IsTransparent := Gif.Images[I].Transparent;
Png := TPngObject.Create; // for new Delphi versions use "TPngImage"
try
if IsTransparent then
begin
Bmp := TBitmap.Create;
Bmp.Assign(Gif.Images[I].Bitmap);
Bmp.PixelFormat := pf24bit;
Png.Assign(Bmp);
Png.CreateAlpha;
TransparentColor := Gif.Images[I].GraphicControlExtension.TransparentColor;
for Y := 0 to Bmp.Height - 1 do
begin
AlphaScanline := Png.AlphaScanline[Y];
for X := 0 to Bmp.Width - 1 do
begin
Pixel := Png.Pixels[X, Y];
if (Pixel = TransparentColor) then
AlphaScanline^[X] := 0;
end;
end;
Bmp.Free;
end
else
Png.Assign(Gif.Images[I].Bitmap);
Png.SaveToFile(Format('%d.png', [I]));
finally
Png.Free;
end;
end;
finally
Gif.Free;
end;
end;