I need to change a single color (clLime, shipped by us) on a bitmap
palette to a different color (various, user selected depending on
variables). When I have done this with a loop, it worked fine on my 64k
color machine, but the colors were all wrong on a 256 color machine. So
I figure that the palette is the problem. Is there any way of making
sure that the colors I need are avaiable on the bitmap canvas?

And, I was thinking that I should be able to just change the one color
in the palette that I know needs to be changed, not have to loop through
the whole canvas. Am I right? How would I do this?

Thanks
Ed Dressel

news:387A52D0.D9B50A6A@brandentech.com...

What is the PixelFormat of your image?  pf8bit or pf24bit?

How are you changing the color?  Are you using the canvas.Pixels
property (which will be fairly slow), or are you changing the palette
and filling in the Scanlines?

While working on pf8bit scanline examples, described at
http://www.efg2.com/Lab/ImageProcessing/Scanline.htm, I observed
the only way I obtained reliable results was to set the palette for a new
bitmap and then fill in the scanlines.   This is fairly fast using the
Scanline property.

I'm only guessing, but when you try to change a palette on a bitmap
and leave the scanlines untouched, Windows tries to find the "nearest"
color for you and can modify the scanline data as part of what it does.
I found I had to fill in the scanline data once the palette was set to
get reliable results.

For links about using palettes in Delphi, try Section A of
http://www.efg2.com/Lab/Library/Delphi/Graphics/Algorithms.htm

--
efg

Earl F. Glynn     E-Mail:  EarlGl...@att.net
Overland Park, KS  USA

efg's Computer Lab:  http://www.efg2.com/Lab

Hi Earl,

"Earl F. Glynn" schrieb:

I believe that the right approach here is to use the SetDIBColorTable
API call to replace the respective entries in the DIB's color table.
You then don't need to modify the scanline data.

Greetings, Robert
--
Robert Ro?mair
http://home.t-online.de/home/Robert.Rossmair/
Programming environment: Delphi 5 Professional, WinNT 4.0 SP6

Hi,

Ed Dressel schrieb:

There is a function named "MapBitmapColors" in my rrColors unit
(freeware + source, see http://home.t-online.de/home/Robert.Rossmair/).
Since it works on DIBs, you need Delphi 3 or above to use it.

Greetings, Robert
--
Robert Ro?mair
Programming environment: Delphi 5 Professional, WinNT 4.0 SP6

Ed,

I had a similar problem a while back, and the following worked for me.  Hope
it helps you...

MyBitmap.Handle := CreateMappedBmp(MyBitmap.Handle, [clLime], [NewColor]);

CreateMappedBmp is in the graphics.pas unit.

-Eric Harmon