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# How to use Scanline property of bitmap to read an entire line of pixels into a 2d array?

Posted on 2003-03-10
Medium Priority
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I am trying to read in the RGB Values and currently am using this piece of code using standard image1.canvas.pixels[22,33] = ...
The image i am using is in greyscale so basically i take one of the RGB values and convert it into an integer in the range 0-255.  Below all that Valueofpix function does is do this conversion into 256 grey value.

i.e:

for N := 2 to 511 do
begin
for M := 2 to 383 do
begin
p1 := ValueofPix(image1.Canvas.Pixels[n-1,m-1]);
p2 := ValueofPix(image1.Canvas.Pixels[n,m-1]);
p3 := ValueofPix(image1.Canvas.Pixels[n+1,m-1]);
p4 := ValueofPix(image1.Canvas.Pixels[n-1,m]);
p5 := ValueofPix(image1.Canvas.Pixels[n+1,m]);
p6 := ValueofPix(image1.Canvas.Pixels[n-1,m+1]);
p7 := ValueofPix(image1.Canvas.Pixels[n,m+1]);
p8 := ValueofPix(image1.Canvas.Pixels[n+1,m+1]);
Facefinder[n,m] := ((p1+p2+p3+p4+p5+p6+p7+p8)/8);
end;
end;

I have been told that scan line is so much more quicker albeit less easier (as i have found) but i would like to use scanline for the speed issue regarding my program.  Any help would be helpful heh

Thx alot i also need an answer fairly soon i.e. by tuesday night.  Thx
0
Question by:DarkGant
• 6
• 4

LVL 1

Expert Comment

ID: 8107044
How have you drawn to the canvas?

If you have loaded a bitmap then the Scanline property is available with the Bitmap property of TImage.Picture and is the way to access the bitmap data of a Windows DIB associated with the Image(BMP files or files that are converted to a DIB on reading). You read the scanline like any other array.  Delphi Help on Scanline has a very good coding example.

Regards
Roger Fedyk
0

LVL 9

Expert Comment

ID: 8109961
type
TRGB32 = packed record
B, G, R, A: Byte;
end;
TRGB32Array = packed array[0..MaxInt div SizeOf(TRGB32)-1] of TRGB32;
PRGB32Array = ^TRGB32Array;

TRGB24 = packed record
B, G, R: Byte;
end;
TRGB24Array = packed array[0..MaxInt div SizeOf(TRGB24)-1] of TRGB24;
PRGB24Array = ^TRGB24Array;

function Pixel32Color(bmp: TBitmap; const X, Y: integer): TColor;
begin
with PRGB32Array(bmp.ScanLine[Y])[X] do
Result := TColor(RGB(R, G, B));
end;

function Pixel24Color(bmp: TBitmap; const X, Y: integer): TColor;
begin
with PRGB24Array(bmp.ScanLine[Y])[X] do
Result := TColor(RGB(R, G, B));
end;

var
bmp: TBitmap;
begin
bmp := Image1.Picture.Bitmap;
bmp.PixelFormat := pf24bit; // or pf32bit; or comment out if you have already
for N := 2 to 511 do begin
for M := 2 to 383 do begin
p1 := ValueofPix(Pixel24Color(bmp, n-1, m-1));
p2 := ValueofPix(Pixel24Color(bmp, n, m-1));
p3 := ValueofPix(Pixel24Color(bmp, n+1, m-1));
p4 := ValueofPix(Pixel24Color(bmp, n-1, m));
p5 := ValueofPix(Pixel24Color(bmp, n+1, m));
p6 := ValueofPix(Pixel24Color(bmp, n-1, m+1));
p7 := ValueofPix(Pixel24Color(bmp, n, m+1));
p8 := ValueofPix(Pixel24Color(bmp, n+1,m+1));
Facefinder[n,m] := ((p1+p2+p3+p4+p5+p6+p7+p8)/8);
end;
end;
end;

mo.
0

LVL 9

Expert Comment

ID: 8110323
to get 8bit (256) pixel color using scanlines:

uses Windows;

type
TPal256EntryArray = array[0..255] of TPaletteEntry;
PPalEntryArray = ^TPal256EntryArray;

function Pixel8Color(bmp: TBitmap; pal: PPalEntryArray; const X, Y: integer): TColor;
begin
with pal[PByteArray(bmp.ScanLine[Y])[X]] do
Result := TColor(RGB(peRed, peGreen, peBlue));
end;

var
bmp: TBitmap;
pe: TPal256EntryArray;
begin
bmp := Image1.Picture.Bitmap;
bmp.PixelFormat := pf8bit;
Res := GetPaletteEntries(bmp.Palette, 0, 256, pe);
if res > 0 then begin
for N := 2 to 511 do begin
for M := 2 to 383 do begin
p1 := ValueofPix(Pixel8Color(bmp, @pe, n-1, m-1));
p2 := ValueofPix(Pixel8Color(bmp, @pe, n, m-1));
p3 := ValueofPix(Pixel8Color(bmp, @pe, n+1, m-1));
p4 := ValueofPix(Pixel8Color(bmp, @pe, n-1, m));
p5 := ValueofPix(Pixel8Color(bmp, @pe, n+1, m));
p6 := ValueofPix(Pixel8Color(bmp, @pe, n-1, m+1));
p7 := ValueofPix(Pixel8Color(bmp, @pe, n, m+1));
p8 := ValueofPix(Pixel8Color(bmp, @pe, n+1,m+1));
Facefinder[n,m] := ((p1+p2+p3+p4+p5+p6+p7+p8)/8);
end;
end;
end;
end;
0

Author Comment

ID: 8110511
mocarts i tried the 8 bit version which works fine for the first loop i.e. it gets all the pixel data correctly when N= 2 and M= 2 to 383 for the first line but when it tries to go onto the 2nd line it says:

Scan Line Index out of Range

0

LVL 9

Expert Comment

ID: 8110535
scanlines have zero based index, try this:
for N := 1 to bmp.height -2 do begin
for M := 1 to bmp.width -2 do begin

mo.
0

LVL 9

Expert Comment

ID: 8110563
oo..
you should exchange N and M in loop declarations

for M := 1 to bmp.height -2 do begin
for N := 1 to bmp.width -2 do begin

mo.
0

Author Comment

ID: 8110718
isnt there a quicker way to just place all RGB values into a 2 d array so that i can access them easier?.
0

LVL 9

Accepted Solution

mocarts earned 200 total points
ID: 8110871
type
TPal256EntryArray = array[0..255] of TPaletteEntry;
TColorMatrix = array of array of TColor;  // [Row, Col]
// TColorMatrix = array of array of byte; // if you want to convert in ColorMatrix8 to gray scale (to do it once)

function ColorMatrix8(bmp: TBitmap): TColorMatrix;
var
pe: TPal256EntryArray;
Line: PByteArray;
x, y, res: integer;
begin
if bmp.PixelFormat <> pf8bit then exit;
Res := GetPaletteEntries(bmp.Palette, 0, 256, pe);
if res > 0 then begin
SetLength(Result, bmp.Height);
for y := 0 to bmp.Height -1 do begin
Line := bmp.ScanLine[y];
SetLength(Result[y], bmp.Width);
for x := 0 to bmp.Width -1 do
with pe[line[x]] do
Result[y, x] := TColor(RGB(peRed, peGreen, peBlue));
// or
// Result[y, x] := ValueOfPix(TColor(RGB(peRed, peGreen, peBlue));
end;
end;
end;

0

Author Comment

ID: 8113117
Thx alot for all your help i believe i understand how scanline works a bit better and your code worked wonderfully.  Thx again
0

LVL 9

Expert Comment

ID: 8118200
I wrote stupid inefficient code... :(
Performance will increase only if we get ScanLine and work with it as long as we need it. and then get next.
my functions Pixel32(24,8)Color probably will work slowly than Canvas.Pixel[x,y].. as in every call of these functions they retrieve whole scanline instead of one pixel..
right way is to pass to Pixel32Color scanLine not bitmap.

function Pixel32Color(ScanLine: PRGB32Array; const X: integer): TColor;
begin
with ScanLine[X] do
Result := TColor(RGB(R, G, B));
end;

mo. :(
0

Author Comment

ID: 8123484
thx alot anyways u made my code run fast enough for me (it increased the speed by a factor of 2 :) )

So thx alot if id have had more points id have given u more
0

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