Mega Code Archive
How to convert a color graphic into gray scale
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Title: How to convert a color graphic into gray scale
Question: How to convert a color graphic into gray scale
Answer:
procedure TForm1.Button1Click(Sender: TObject);
var
lo:tbitmap;
i,j:integer;
kl:longint;
rr,gg,bb:byte;
res:byte;
begin
lo:=tbitmap.create;
lo.Width:=image1.Width;
lo.height:=image1.height;
ProgressBar1.Max:=image1.Width+1;
for i:=0 to image1.Width+1 do
begin
for j:=0 to image1.height+1 do
begin
kl:=ColorToRGB(image1.Canvas.Pixels[i,j]);
rr:=byte(kl);
gg:=byte(kl shr 8);
bb:=byte(kl shr 8);
res:=(rr+gg+bb) div 3;
lo.Canvas.Pixels[i,j]:=rgb(res,res,res);
end;
ProgressBar1.Position:=i;
end;//for do
image1.Canvas.Draw(0,0,lo);
lo.free;
end;
the principle on which the code work is actually very simple
what is happening is that when you evaluete a color variable you will see that it consists of 4 parts. red green blue and windows pallete info this is split up like this
FF FF FF FF
Palletteinfo blue green red
when the blue,green and red values are added together and are devided by 3 you will always get a grey value.
This procedure works by moving the value we want to right
and then typecasting it to a byte. When we typcast something the we start with the least significant bit and work our way up until it is equal in size to the variable we are typecasting it.
if we look at a binary representation it looks like this
1111 1111 1111 1111 1111 1111 1111 1111 this is white
1111 1111 1111 1111 0000 0000 0000 0000 this is blue
{byte }
when a value like the above is shr the following happens
it changes to:
0000 0000 1111 1111 1111 1111 0000 0000 this is now yellow
this code is not very fast and can definitly be improved what could be used is the scanline procedure of tbitmap which would probably speed up things.
if you only want to split the rgb channels instead of counting the 3 rgb values together use each seperately to draw each channel.
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