TIEBitmap.HasAlphaChannel

Declaration

function HasAlphaChannel(Validate: Boolean = False): boolean;

Description

Specifies whether the current image has an alpha channel.

If Validate is False, HasAlphaChannel will return true even if the alpha channel is not used (image is completely opaque, but AlphaChannel is valid).
If Validate is true, it will check that the image uses the alpha channel, i.e. some parts of the image are transparent. The AlphaChannel is removed if not used.

Examples

if ImageEnView1.IEBitmap.HasAlphaChannel() then...  // Image has alpha channel, may or may not be used

if ImageEnView1.IEBitmap.HasAlphaChannel( True ) then...  // Image has alpha channel, part of the image are transparent

// Show the percentage of pixels that are partially or fully transparent
// Same as TImageEnProc.CalcImageNumColors()
var
  px: pbyte;
  y, x, l: integer;
  alphaCount, denom: Integer;
  bmp: TIEBitmap;
begin
  bmp := ImageEnView1.IEBitmap;

  alphaCount := 0;
  if bmp.HasAlphaChannel() then
  begin
    l := IEBitmapRowLen( bmp.AlphaChannel.Width, bmp.AlphaChannel.BitCount, 8);
    for y := 0 to bmp.AlphaChannel.Height - 1 do
    begin
      px := bmp.AlphaChannel.Scanline[y];
      for x := 0 to l - 1 do
      begin
        if px^ < 255 then
          Inc( alphaCount );
        inc(px);
      end;
    end;
  end;

  denom := bmp.Width * bmp.Height;
  ShowMessage( format( 'Image has %d%% transparent pixels', [ Round( alphaCount / denom * 100 )]));
end;

if bmp.HasAlphaChannel(True) and bmp.AlphaChannel.IsAllBlack() then
  ShowMessage( 'Image is completely transparent' )
else
  ShowMessage( 'Image NOT transparent' );

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