How to display a 24 bit True Color bitmap image on a 256 color display (Views: 29)
Problem/Question/Abstract: How to display a 24 bit True Color bitmap image on a 256 color display Answer: You can take advantage of the new graphics capabilities of the TBitmap and TJPEGImage components of Delphi 3/4. When Delphi 3/4 loads a bitmap image, it keeps a copy of the device independent bitmap image it loads from a file in the background. The TJPEGImage component is very good at color reducing a full color image down to 256 colors. By Loading the bitmap, then assigning the image to a Jpeg and saving it to a temporary ".JPG" file, you can then load the temporary file back into a TImage with much better results than simply loading the bitmap file unconverted. The following example demonstrates the necessary steps to achieve these results. uses JPEG; procedure TForm1.Button1Click(Sender: TObject); var JP: TJPEGImage; IM: TImage; TempFileName: string; begin {Pop up an Open Dialog} OpenDialog1.Options := [ofNoChangeDir, ofFileMustExist]; OpenDialog1.Filter := 'Bitmap Files (*.bmp)|*.bmp'; if OpenDialog1.Execute then begin {Create a temporary TImage} IM := TImage.Create(nil); {Load the bitmap file} IM.Picture.LoadFromFile(OpenDialog1.FileName); {Create a temporary TJPEGImage} JP := TJPEGImage.Create; {Priority on quality} JP.Performance := jpBestQuality; {Assign the bitmap to the JPEG} JP.Assign(IM.Picture.Graphic); {Free the temp image} IM.Free; {Make a temp file name with the extension of .jpg} TempFileName := 'test.jpg'; {Save the JPEG to a temp file} JP.SaveToFile(TempFileName); {Free the JPEG} JP.Free; {Load the temp file to an image on the form} Image1.Picture.LoadFromFile(TempFileName); {Delete the temp file} DeleteFile(TempFileName); end; end; |