procedure TForm1.MakeTransparentByLightness(ImageEnView: TImageEnView; Threshold: Integer);
var
  x, y: Integer;
  IEBitmap: TIEBitmap;
  AlphaBitmap: TIEBitmap;
  PixelColor: TRGB;
  Lightness: Integer;
  AlphaScanLine: PByteArray;
begin
  ImageEnView.Proc.SaveUndo();

  IEBitmap := ImageEnView.IEBitmap; // Reference to the ImageEnView bitmap

  // Ensure the bitmap has an alpha channel
  if not IEBitmap.HasAlphaChannel then
    IEBitmap.AlphaChannel; // IEBitmap.AlphaChannel.Create alpha channel is undeclared

  AlphaBitmap := IEBitmap.AlphaChannel; // Reference the alpha channel bitmap

  // Process each pixel to make those below or above the threshold transparent
  for y := 0 to IEBitmap.Height - 1 do
  begin
    AlphaScanLine := AlphaBitmap.ScanLine[y];
    for x := 0 to IEBitmap.Width - 1 do
    begin
      // Access the pixel color as TRGB
      PixelColor := IEBitmap.Pixels_ie24RGB[x, y];

      // Calculate the Lightness value
      Lightness := PARGBToIntL(PixelColor);

      if Lightness <= Threshold then
        AlphaScanLine[x] := 0 // Make pixel fully transparent
      else
        AlphaScanLine[x] := 255; // Make pixel fully opaque
    end;
  end;

  // Ensure the alpha channel is in sync
  IEBitmap.SyncAlphaChannel;

  // Force the component to redraw:
  ImageEnView.Update;
  IEBitmap.AlphaChannel.SyncFull(); // it works! https://www.imageen.com/ieforum/topic.asp?TOPIC_ID=6072
  UpdateStatusBarWithImageEnView(False);
  Self.ActiveControl := ImageEnView;
end;

procedure TForm1.MakeTransparentByLightness(ImageEnView: TImageEnView; Threshold: Integer);
var
  x, y: Integer;
  IEBitmap: TIEBitmap;
  AlphaBitmap: TIEBitmap;
  PixelColor: TRGB;
  Lightness: Integer;
  AlphaScanLine: PByteArray;
  HasSelection: Boolean;
begin
  ImageEnView.Proc.SaveUndo();

  IEBitmap := ImageEnView.IEBitmap; // Reference to the ImageEnView bitmap

  // Ensure the bitmap has an alpha channel
  if not IEBitmap.HasAlphaChannel then
    IEBitmap.AlphaChannel;

  AlphaBitmap := IEBitmap.AlphaChannel; // Reference the alpha channel bitmap

  // Check if there is an existing selection
  HasSelection := not ImageEnView.SelectionMask.IsEmpty;

  // Process each pixel to make those below or above the threshold transparent
  for y := 0 to IEBitmap.Height - 1 do
  begin
    AlphaScanLine := AlphaBitmap.ScanLine[y];
    for x := 0 to IEBitmap.Width - 1 do
    begin
      // Check if the pixel is within the selection or if no selection exists
      if (not HasSelection) or (ImageEnView.SelectionMask.IsPointInside(x, y)) then
      begin
        // Access the pixel color as TRGB
        PixelColor := IEBitmap.Pixels_ie24RGB[x, y];

        // Calculate the Lightness value
        Lightness := PARGBToIntL(PixelColor);

        if Lightness <= Threshold then
          AlphaScanLine[x] := 0 // Make pixel fully transparent
        else
          AlphaScanLine[x] := 255; // Make pixel fully opaque
      end;
    end;
  end;

  // Ensure the alpha channel is in sync
  IEBitmap.SyncAlphaChannel;

  // Force the component to redraw
  ImageEnView.Update;
  IEBitmap.AlphaChannel.SyncFull;
  UpdateStatusBarWithImageEnView(False);
  Self.ActiveControl := ImageEnView;
end;