procedure Grayscale(const Bitmap:TBitmap);
var
X: Integer;
Y: Integer;
R,G,B,Gray: Byte;
Color: TColor;
begin
for Y := 0 to (Bitmap.Height - 1) do
begin
for X := 0 to (Bitmap.Width - 1) do
begin
Color := Bitmap.Canvas.Pixels[X,Y];
R := Color and $FF;
G := (Color and $FF00) shr 8;
B := (Color and $FF0000) shr 16;
Gray := Trunc(0.3 * R + 0.59 * G + 0.11 * B);
Bitmap.Canvas.Pixels[X,Y] := Gray shl 16 or Gray shl 8 or Gray;
end
end
end;
{这段代码效率是非常低的,但可以方便我们理解同时一些问题}
Delphi的帮助中对TColor已经有了详细的描述,这可以方便我们理解上面的代码!
首先看:
R := Color and $FF;
G := (Color and $FF00) shr 8;
B := (Color and $FF0000) shr 16;
procedure Grayscale(const Bitmap:TBitmap);
const
PixelCountMax = 32768;
type
pRGBTripleArray = ^TRGBTripleArray;
TRGBTripleArray = ARRAY[0..PixelCountMax-1] OF TRGBTriple;
var
Row: pRGBTripleArray;
X: Integer;
Y: Integer;
Gray: Byte;
begin
for Y := 0 to (Bitmap.Height - 1) do
begin
Row := Bitmap.ScanLine[Y];
for X := 0 to (Bitmap.Width - 1) do
begin
Gray := Trunc(0.3 * Row^[X].rgbtRed + 0.59 * Row^[X].rgbtGreen + 0.11 * Row^[X].rgbtBlue);
Row^[X].rgbtRed:=Gray;
Row^[X].rgbtGreen:=Gray;
Row^[X].rgbtBlue:=Gray;
end;
end;
end;
procedure Grayscale(const Bitmap:TBitmap);
var
X: Integer;
Y: Integer;
PRGB: pRGBTriple;
Gray: Byte;
begin
for Y := 0 to (Bitmap.Height - 1) do
begin
PRGB := Bitmap.ScanLine[Y];
for X := 0 to (Bitmap.Width - 1) do
begin
Gray := Trunc(0.3 * PRGB^.rgbtRed + 0.59 * PRGB^.rgbtGreen + 0.11 * PRGB^.rgbtBlue);
PRGB^.rgbtRed:=Gray;
PRGB^.rgbtGreen:=Gray;
PRGB^.rgbtBlue:=Gray;
Inc(PRGB);
end;
end;
end;
for Y := 0 to (Bitmap.Height - 1) do
begin
p := Bitmap.ScanLine[Y];
for X := 0 to (Bitmap.width - 1) DIV 8 + 1 do
begin
p^:=1 or 2 or 4 or 8 or 16 or 32 or 64 or 128;
Inc(PRGB,3);
end;
end;
p^:=1 or 2 or 4 or 8 or 16 or 32 or 64 or 128;
这行代码什么意思呢?1=1(二进制),2=10(二进制),4=100(二进制),8=1000(二进制)...
for j := 0 TO Bitmap.Height-1 DO
begin
Row15 := Bitmap15.Scanline[j];
Row24 := Bitmap24.Scanline[j];
for i := 0 TO Bitmap.Width-1 DO
begin
with Row24^ do
Row15^ := (rgbtRed Shr 3) Shl 10 or (rgbtGreen Shr 3) Shl 5 or (rgbtBlue Shr 3);
Inc(Row24);
Inc(Row15);
end
end;
procedure Grayscale(const Bitmap:TBitmap);
var
X: Integer;
Y: Integer;
PRGB: pRGBTriple;
Gray: Byte;
begin
for Y := 0 to (Bitmap.Height - 1) do
begin
PRGB := Bitmap.ScanLine[Y];
for X := 0 to (Bitmap.Width - 1) do
begin
Gray := Trunc(0.3 * PRGB^.rgbtRed + 0.59 * PRGB^.rgbtGreen + 0.11 * PRGB^.rgbtBlue);
PRGB^.rgbtRed:=Gray;
PRGB^.rgbtGreen:=Gray;
PRGB^.rgbtBlue:=Gray;
Inc(PRGB);
end;
end;
end;
实际应用中,这种方法已经很快了,但实际上还存在可以优化的余地,什么呢?
Gray := Trunc(0.3 * Red + 0.59 * Green + 0.11 * Blue);//这句用的是浮点运算
在图像处理中,速度就是生命,能不用浮点运算,就最好不要用!
Gray := (30 * Red + 59 * Green + 11 * Blue) div 100;
虽然这样一改,运算次数多了一次,但在我的雷鸟1.1G上,处理速度大概能提高5%左右!而同主频下(或略低,如Athlon 1600+相当于P4 1.6G)AMD的CPU浮点运算能力比Intel的较强,整数运算能力较弱,所以用Intel的CPU在这里更能体现出优势!
注:x div 100 和 Trunc(x/100)的效果是相同的,但查看其汇编代码可知一个用的指令是div,而另一个是fdiv(即进行浮点运算),还要调用函数Trunc,其处理速度差距非常大,所以能用 x div 100 的时候就不要用 Trunc(x/100)。
但这还不是最快的,再看一个:
Gray := HiByte(77 * Red + 151 * Green + 28 * Blue);
即
Gray := (77 * Red + 151 * Green + 28 * Blue) shr 8;
(建议用后一种,不要调用函数)