Grayscale
lazarus / 39-Graphics

----------------------------------------------------------------------
pcurtis · 2020-06-09 07:18

How can I convert a colour image into grayscale?

P.S. I dont want to use external tools.

Thanks in advance.

----------------------------------------------------------------------
eljo · 2020-06-09 07:36

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i uses   
Graphics, GraphUtiuls, .....; procedure ToGrayscale(const
aBMP:TBitmap);var  X, Y: Integer;begin   For X :=0 to aBMP.Width -1
do    For Y := 0 to aBmp.Height -1 do begin     
aBmp.Canvas.Pixels[X,Y] :=  ColorToGray(aBmp.Canvas.Pixels[X,Y]);   
End;end; 
Warning the above code is just a hint. It has never been compiled or
checked for errors and of course this is not a recommendation on how
to do it. In fact I would suggest to avoid the pixels property at all
costs.

----------------------------------------------------------------------
pcurtis · 2020-06-09 07:44

Cant it be be done in one operation?

----------------------------------------------------------------------
eljo · 2020-06-09 07:55

Quote from: pcurtis on June 09, 2020, 09:44:18 amCant it be be done in
one operation?
no. an image is a collection of pixels you need to convert each pixel
individually.

----------------------------------------------------------------------
circular · 2020-06-09 08:14

With BGRABitmap you can with the InplaceGrayscale function.

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i image :=
TBGRABitmap.Create('image.png');image.InplaceGrayscale(True); //with
gamma correction

----------------------------------------------------------------------
wp · 2020-06-09 08:29

Quote from: eljo on June 09, 2020, 09:36:42 amIn fact I would suggest
to avoid the pixels property at all costs.

Yes, the Pixels property is very slow. This is a faster version using
LazIntfImage:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i uses 
LCLType, FPImage, IntfGraphics; procedure ToGrayscale(const ABitmap:
TBitmap);var  img: TLazIntfImage;  i, j: Integer;  clr: TFPColor; 
gray: Word;  bmpHandle, maskHandle: HBitmap;begin  img :=
ABitmap.CreateIntfImage;  for j := 0 to img.Height - 1 do    for i :=
0 to img.Width - 1 do    begin      clr := img.Colors[i, j];      gray
:= (clr.Red + clr.Green + clr.Blue) div 3;      clr.Red := gray;     
clr.Green := gray;      clr.Blue := gray;      img.Colors[i, j] :=
clr;    end;  img.CreateBitmaps(bmpHandle, maskHandle); 
ABitmap.Handle := bmpHandle;  ABitmap.MaskHandle := maskHandle;end;

----------------------------------------------------------------------
pcurtis · 2020-06-09 08:43

@Circular - Thanks, its simple and works.

@wp, I'll have a look later

----------------------------------------------------------------------
PaulRowntree · 2020-06-09 17:43

If you are trying to maintain visual comparisons, the three colour
components are usually not equally weighted.

https://en.wikipedia.org/wiki/Grayscale

----------------------------------------------------------------------
flowCRANE · 2020-06-15 18:47

Fastest way, no external libraries needed, no temporary image needed,
good final quality:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
GrayBuffer(ABuffer: TBitmap);type  TBitmapPixel = record B, G, R:
UInt8 end; type  PBitmapLine = ^TBitmapLine;  TBitmapLine = array
[UInt16] of TBitmapPixel;var  Line: PBitmapLine;  LineIndex,
PixelIndex: Integer;  GrayShade: UInt8;begin  ABuffer.BeginUpdate();  
for LineIndex := 0 to ABuffer.Height - 1 do  begin    Line :=
ABuffer.ScanLine[LineIndex];     for PixelIndex := 0 to ABuffer.Width
- 1 do      with Line^[PixelIndex] do      begin        GrayShade :=
Round(0.299 * R + 0.587 * G + 0.114 * B);              B :=
GrayShade;        G := GrayShade;        R := GrayShade;      end; 
end;   ABuffer.EndUpdate();end;