一个将图像的某个区域之外的区域变暗的函数

过程名: DarkBmp

作者: 不得闲

日期: 2009.02.04

参数: bmp: TBitmap;var DarkRect: TRect;const DarkValue: Integer;const HighValue: Integer = 0

DarkRect指定不变暗的区域

DarkValue: 指定暗化的数量值

HighValue: 指定矩形区域增亮化的数量值

功能： 将图像的某个区域之外的区域变暗的函数

返回值: 无

procedure DarkBmp(bmp: TBitmap;var DarkRect: TRect;const DarkValue: Integer;const HighValue: Integer = 0);
var
i,j : integer;
pB : PByteArray;
BmpFormatXs: Integer;
w,h:Integer;
begin
i := Integer(bmp.PixelFormat);
if i < 4 then
i := 4
else if i = 4 then
inc(i)
else if i > 7 then
i := 7;
BmpFormatXs := i - 3;
w:= DarkRect.Right - DarkRect.Left;
h:= DarkRect.Bottom - DarkRect.Top;

if DarkRect.Right > bmp.Width then
begin
DarkRect.Left:=bmp.Width - w;
DarkRect.Right:=bmp.Width;
end;
if (DarkRect.Bottom > bmp.Height) then
begin
DarkRect.Top:= bmp.Height - h;
DarkRect.Bottom:=bmp.Height;
end;
if DarkRect.Left <0 then
begin
DarkRect.Left:=0;
DarkRect.Right:=w;
end;
if DarkRect.Top <0 then
begin
DarkRect.Top:=0;
DarkRect.Bottom:=h;
end;
for i := 0 to DarkRect.Top - 1 do
begin
pb:=bmp.ScanLine[i];
for j:=0 to BmpFormatXs*bmp.Width - 1 do
if pb[j]<DarkValue then
pb[j]:=0
else dec(pb[j],DarkValue);
end;
for i := DarkRect.Top to bmp.Height - 1 do
begin
pb:=bmp.ScanLine[i];
for j:=0 to BmpFormatXs*DarkRect.Left - 1 do
if pb[j]<DarkValue then
pb[j]:=0
else dec(pb[j],DarkValue);
end;
for i := DarkRect.Bottom to bmp.Height - 1 do
begin
pb:=bmp.ScanLine[i];
for j:= BmpFormatXs*DarkRect.Left to BmpFormatXs*bmp.Width - 1 do
if pb[j]<DarkValue then
pb[j]:=0
else dec(pb[j],DarkValue);
end;
for i := DarkRect.Top to DarkRect.Bottom - 1 do
begin
pb:=bmp.ScanLine[i];
for j:= BmpFormatXs*DarkRect.Right to BmpFormatXs*bmp.Width - 1 do
if pb[j]<DarkValue then
pb[j]:=0
else dec(pb[j],DarkValue)
end;
if HighValue <> 0 then
for i := DarkRect.Top to DarkRect.Bottom - 1 do
begin
pb:=bmp.ScanLine[i];
for j:= BmpFormatXs*DarkRect.Left to BmpFormatXs*DarkRect.Right - 1 do
if pb[j]>(255-DarkValue) then
pb[j]:=255
else inc(pb[j],HighValue);
end;
end;

使用方法：
procedure TForm1.Button1Click(Sender: TObject);
var
bmp: TBitmap;
r: TRect;
begin
bmp := TBitmap.Create;
bmp.Assign(Image1.Picture.Bitmap);
r := Rect(0,0,50,50);
DarkBmp(bmp,r,40,10);
Image2.Picture.Bitmap := bmp;
end;