本文整理自网络，侵删。
所谓轮廓提取就是掏空图形的内部点：如果原图中有一点为黑，且它的8个相邻点都是黑色时（此时该点是内部点），则将该点删除。
procedure GetFigure(Bitmap: TBitmap);
var
b0, b1: Tbitmap;
i, j: Integer;
p1, p2, p3, p4: pbyteArray;
begin
b0 := Tbitmap.Create;
b1 := Tbitmap.Create;
b0.Assign(Bitmap);
b1.Assign(Bitmap);
b0.PixelFormat := pf24bit;
b1.PixelFormat := pf24bit;
for i := 1 to b0.Height - 2 do
begin
//扫描三条三邻的像素行
p1 := b0.ScanLine[i - 1];
p2 := b0.ScanLine[i];
p3 := b0.ScanLine[i + 1];
p4 := b1.ScanLine[i];
for j := 1 to b0.Width - 2 do
begin
if (p2[3 * j + 2] = 0) and (p2[3 * j + 1] = 0) and (p2[3 * j] = 0) then
begin
if ((p2[3 * (j - 1) + 2] = 0) and (p2[3 * (j - 1) + 1] = 0) and (p2[3 * (j - 1)] = 0)) and
((p2[3 * (j + 1) + 2] = 0) and (p2[3 * (j + 1) + 1] = 0) and (p2[3 * (j + 1)] = 0)) and
((p1[3 * (j + 1) + 2] = 0) and (p1[3 * (j + 1) + 1] = 0) and (p1[3 * (j + 1)] = 0)) and
((p1[3 * (j) + 2] = 0) and (p1[3 * (j) + 1] = 0) and (p1[3 * (j)]= 0)) and
((p1[3 * (j - 1) + 2] = 0) and (p1[3 * (j - 1) + 1] = 0) and (p1[3 * (j - 1)] = 0)) and
((p3[3 * (j - 1) + 2] = 0) and (p3[3 * (j - 1) + 1] = 0) and (p3[3 * (j - 1)] = 0)) and
((p3[3 * (j) + 2] = 0) and (p3[3 * (j) + 1] = 0) and (p3[3 * (j)]= 0)) and
((p3[3 * (j + 1) + 2] = 0) and (p3[3 * (j + 1) + 1] = 0) and (p3[3 * (j + 1)] = 0)) then
begin
p4[3 * j + 2] := 255;
p4[3 * j + 1] := 255;
p4[3 * j] := 255;
end;
end;
end;
Bitmap.Assign(b1);
end;
b1.Free;
b0.Free;
end;
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