Hi,

After learning Delphi 5 for a while, I'm beginning to explore on the
graphics portion. A question - how do I create an interlace (TV lines)
effect on a TBitmap, and how can I vary the thickness of the lines, and the
'distance' between the lines.  Any help would be great!

Rgds
Ron

The easiest version would be

Bitmap.Canvas.Pen.Color := clBlack;
y := 0;
while y < Bitmap.Height do begin
  Bitmap.Canvas.MoveTo (0,y);
  Bitmap.Canvas.LineTo (Bitmap.Width,y);
  inc (y,2);
end;

Probably you want the lines not to be completely black but just a bit
darker. I recommend to use the ScanLine property (on a 24 or 32 bit
bitmap), do basically the same as above, but use a pointer that steps
through the lines and does something like Ptr^.Red := Ptr^.Red DIV 2
etc. (more on ScanLines can be found on
http://www.efg2.com/Lab/ImageProcessing/Scanline.htm)

inc (y,3) instead of (inc (y,2) makes the distance greater, for thicker
lines simply draw several ones directly after one another.

Jens

Hi Jens,

Thanks a lot.   I tried using another method of changing 'even' lines to
clBlack, and not touching the odd lines.  It worked like a standard
interlaced image.. but your method allows changing pen size.. which is what
I would like to do... Will explore your method as suggested.

Rgds
Ron

news:3C0AB8C6.6DA00175@pegtop.net...

The Even-Odd-Method brought me to an idea (even-odd is nothing but y MOD
2 = 0/1). This one is easier to cope with...

Bitmap.Canvas.Pen.Color := clBlack;
y := 0;
while y < Bitmap.Height do begin
  if (y MOD (SpaceBetweenLine+LineThickness)) < LineThickness then begin
    Bitmap.Canvas.MoveTo (0,y);
    Bitmap.Canvas.LineTo (Bitmap.Width,y);
  end;
  inc (y,1);
end;

Jens

Jens,

Yes... and by making the Pen.Color a variable, you'll have a VENETIAN BLIND
filter!. This is great.... :)

Rgds
Ronnie

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