Convert BMP of 24 bits to 8 bits

John

Delphi Developer

Convert BMP of 24 bits to 8 bits

2006-11-06 07:26:19 PM
delphi35
Hello,
I have a BMP of 24 bits that has a maximum of 32 colors used, how would
like to compress it to a 8 bit bitmap, any tips ?
thanks
John

Nicholas Sherlock

Delphi Developer

2006-11-06 08:38:49 PM

Re:Convert BMP of 24 bits to 8 bits

John writes:

Quote

I have a BMP of 24 bits that has a maximum of 32 colors used, how would
like to compress it to a 8 bit bitmap, any tips ?
Since you know that there is <=256 colors, this should be fairly easy.

I'd look at using some sort of hashing structure to store the palette
index for each pixel. Just iterate over the pixels in the image, look up
in the hash table to see if they have been assigned an entry, if not,
allocate one and put back into the table.
Alternatively, if your bitmaps are small or speed is not an issue, you
could just use a 256-entry array and do a linear search for each pixel.
Cheers,
Nicholas Sherlock
--
www.sherlocksoftware.org

John

Delphi Developer

2006-11-07 07:14:08 AM

Re:Convert BMP of 24 bits to 8 bits

Thanks Nicholas!

Andrew Jameson

Delphi Developer

2006-11-07 05:16:39 PM

Re:Convert BMP of 24 bits to 8 bits

Just curious ... what happens when you do Bitmap.PixelFormat := pf8bit ?
... you might expect it to do exactly what John wants but it doesn't.
Andrew

David J Taylor

Delphi Developer

2006-11-07 06:30:06 PM

Re:Convert BMP of 24 bits to 8 bits

Andrew Jameson writes:

Quote

Just curious ... what happens when you do Bitmap.PixelFormat :=
pf8bit ? ... you might expect it to do exactly what John wants but it
doesn't.
Andrew
IIRC, by default it uses the Windows 256 colour palette, and may not give

pleasing results. it is certainly worth a test before writing much
code....
David

Mat Ballard

Delphi Developer

2006-11-08 07:21:17 AM

Re:Convert BMP of 24 bits to 8 bits

John writes:

Quote

I have a BMP of 24 bits that has a maximum of 32 colors used, how would
like to compress it to a 8 bit bitmap, any tips ?
TGifImage.ReduceColors();

5690AD

Delphi Developer

2006-11-17 05:43:19 PM

Re:Convert BMP of 24 bits to 8 bits

John writes:

Quote

Hello,

I have a BMP of 24 bits that has a maximum of 32 colors used, how would
like to compress it to a 8 bit bitmap, any tips ?

thanks

John
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