Setting TBitmap.PixelFormat is broken?

[domasz]

Very simple code. Reading a 24bit BMP, converting to 32bit and saving:

Code: Pascal  [Select][+][-]

1.   Bmp := TBitmap.Create;
2.   Bmp.LoadFromStream(Str);
3.   Bmp.PixelFormat := pf32bit;
4.   Bmp.SaveToFile('hejka.bmp');

Saved image is still 24bpp.

[marcov]

Setting the pixel format afaik doesn't convert. It just prepares the buffer for the next (write to the image) action to be 32-bit sized.

[domasz]

So this needs to be changed because in Delphi this does convert and is used by a lot of graphic libraries and functions.

[theo]

You could try this:

Code: Pascal  [Select][+][-]

1. uses FPReadBMP, FPImage, FPWriteBMP;
2. ....
3. var
4.   Image: TFPCustomImage;
5.   Reader: TFPCustomImageReader;
6.   Writer: TFPWriterBMP;
7. begin
8.   Image := TFPMemoryImage.Create(10, 10);
9.   Reader := TFPReaderBMP.Create;
10.   Writer := TFPWriterBMP.Create;
11.   Image.LoadFromFile('test.bmp', Reader);
12.   Writer.BitsPerPixel:=32;
13.   Image.SaveToFile('test32.bmp', Writer);
14.   Image.free;
15.   Reader.free;
16.   Writer.free;
17. end;    

[KodeZwerg]

Hello theo, thank you for your snippet, I just tried it, partially I can transform BPP from-to but now I run into an error where the created file is 0 byte.
Is there also a method to convert/adjust palette for destination BPP?

My try was to convert from 32bpp to 8bpp.

[KodeZwerg]

Setting the pixel format afaik doesn't convert. It just prepares the buffer for the next (write to the image) action to be 32-bit sized.

I did try what you was writing, unsuccessful.
I loaded 32bpp Bitmap and create a second TBitmap with 16bits PixelFormat, draw the source on and saved = 32bpp 

[theo]

My try was to convert from 32bpp to 8bpp.

For 8bpp you need a palette (Color Quantization).
I don't know how to do this with fpImage.
It seems to work with BGRABitmap though.
See: https://forum.lazarus.freepascal.org/index.php/topic,61252.0.html

[KodeZwerg]

My try was to convert from 32bpp to 8bpp.

For 8bpp you need a palette (Color Quantization).
I don't know how to do this with fpImage.
It seems to work with BGRABitmap though.
See: https://forum.lazarus.freepascal.org/index.php/topic,61252.0.html

Thanks! That was what I needed for my little project to easy reduce/slim very big pictures! (yes, with loss of colors...)