TImageEnProc.CastAlpha

Declaration

procedure CastAlpha(BmpX, BmpY: Integer; NewAlpha: Integer; Tolerance: Integer; SampleSize: Integer = 1; MaxFilter: Boolean = False; ColorFill: TColor = clNone);

Description

Perform a flood-fill starting at the bitmap coordinates BmpX, BmpY, i.e. replacing all encountered pixels that match the color at the starting position with alpha.

Parameter	Description
BmpX, BmpY	Pixel specifying the color to be made alpha
NewAlpha	Specifies the Alpha level to apply to matching pixels in the range 0: Fully Transparent - 255: Opaque
Tolerance	The maximum difference from the starting pixel (0 to 255, where 0 requires an exact color match, whereas 255 would match every color)
SampleSize	The diameter of the area to sample (centered on BmpX, BmpY) to determine the seed color. If 1 is specified (Default) only the color of the specified pixel is used
MaxFilter	Apply a maximum filter for more aggressive color selection (remove the "black hole")
ColorFill	Specify to also fill the matching pixels with the specified color. The image must be ie24RGB

Note:
◼ To flood fill an area to a new color, use CastColor
◼ If the image PixelFormat is not ie24RGB, it will be converted
◼ An AlphaChannel will be added to the image, if it does not exist
◼ A UI for this is available to your users in the Image Processing dialog

CastColor vs CastAlpha

These methods can be used interchangeably.

// These two methods have the same effect (Flood filling Red)...
ImageEnView1.Proc.CastColor( x, y, clRed { NewColor }, 0, 1, False, -1 { NewAlpha } );
ImageEnView1.Proc.CastAlpha( x, y, -1 { NewAlpha }, 0, 1, False, clRed { NewColor } );

// These two methods have the same effect (Flood filling alpha to 125)...
ImageEnView1.Proc.CastColor( x, y, clNone { NewColor }, 0, 1, False, 125 { NewAlpha } );
ImageEnView1.Proc.CastAlpha( x, y, 125 { NewAlpha }, 0, 1, False, clNone { NewColor } );

// These two methods have the same effect (Flood filling Red with alpha of 255)...
ImageEnView1.Proc.CastColor( x, y, clRed { NewColor }, 0, 1, False, 255 { NewAlpha } );
ImageEnView1.Proc.CastAlpha( x, y, 255 { NewAlpha }, 0, 1, False, clRed { NewColor } );

Demo

Demos\ImageEditing\EveryMethod\EveryMethod.dpr

Examples

// Assuming X, Y are mouse coordinates, make the area transparent
ImageEnView1.Proc.CastAlpha( ImageEnView1.XScr2Bmp(X), ImageEnView1.YScr2Bmp(Y), 0, 0 );

// On mouse down flood fill the area opaque with a blue fill
procedure TForm1.ImageEnView1MouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
ImageEnView1.Proc.CastAlpha( ImageEnView1.XScr2Bmp(X), ImageEnView1.YScr2Bmp(Y), 255, 0, 1, False, clBlue );
end;

// Load test image
ImageEnView1.IO.LoadFromFile( 'D:\TestImage.jpg' );

// Flood file transparency from the top-left of the image
ImageEnView1.Proc.CastAlpha( 0, 0, 0, 50 );

TImageEnProc.CastAlpha