Convert a 32Bit Png to a 24bit Bitmap - graphics

Question

What I'm trying to do is process a downloaded image at a pixel level, in a vb6 console application, these are the steps currently
I download a png file from a website, this comes down as a 32 bit image, the image is grey scale, when the image is first
downloaded I need to convert it to a 24 bit Bitmap in order to be able to process it, if I open the image in Paint and save
it as a 24 bit bitmap I'm able to process the image without issue, when saving in Paint I dod get a message when saving that
says "Any Transparency will be lost if you save this picture.", Once saved, I then do a binary read on the file then extract the
BITMAPFILEHEADER
BITMAPINFOHEADER
BMPData
I can then loop through the BMPData and extract and process the needed value's. If I try to load the image without first saving
it to a 24 bit bitmap in paint, I receive a an out of memory error in VB (Run-Time Error 7) and the BMPInfoHeader.biSizeImage is
very big compaired to the size it is after with has been saved via paint.
I have tried to convert with ImageMagick-6.9.0-Q16 ad and GraphicsMagick-1.3.21-Q8 but these just seem to mess up the converted file.
Anyone got any idea's ?
Regards
Potman100

Answer 1

I have tried everything I know to get ImageMagick to create a 24-bit colour BMP from a greyscale 32-bit PNG file, including:
+matte to remove the alpha channel
-type truecolor to force a colour output
BMP4:output.bmp to force a BMP4
BMP3:output.bmp to force a BMP3
BMP2:output.bmp to force a BMP2
-colors 16|256 to force number of colours
-depth 8|24 to set the bit depth
passing through PPM format and back to get rid of PNG settings
writing via NetPBM's ppm2bmp/ppmtobmp
and all to no avail. I cannot get ImageMagick to create a 24-bit color BMP from a grey 32-bit PNG.
Update
I have worked out a horrible hack that will make you a 24-bit BMP, as follows. In a greyscale image, the Red=Green=Blue intensity for every pixel. If we decide to multiply every Blue pixel by 0.99, then, with just 1% error, the blue pixel will be less than the red and green, so ImageMagick will simply be unable to use a grayscale image to save the BMP in... like this:
convert input.png +matte -channel B -evaluate multiply 0.99 image.bmp
I don't know if that will work for you, if so, good, stop here. If not, continue...
The only thing I can suggest is that you use PPM format which is even easier than BMP for you to read from
convert yourImage.png output.ppm
That will get you a P6 type PPM image, as described here. If you want the even easier ASCII P3 version, use this command
convert yourImage.png -compress none output.ppm
and your image will look like this:
P3
384 128
255
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 255 255 255

Answer 2

Wow, thanks for all the time and effort you have taken to try and get a working solution for me,
I have tried the above and probably the one that will work is
convert yourImage.png -compress none output.ppm
I would have to do some further testing to check the values, but I think it would work.
The need to be able to create a 24bit bitmap is part of a project I am doing, the site I get
the png image from generates this image to offer a £ price for an item that I may sell to
them, so the png will contain a £ Value (i.e £ 1.56), I wanted to be able to work out the
value of the offer in a dos program I have written, so it can be called from php.
I did find a way to do it, I use xmlhttp to download the image via an adodb stream and found
that I could save the image in a number of different formats other than a bmp, so I looked
at the format of different image formats and found that the tif file format look promising
and found some code online that used Microsoft Image Acquistion Library to manipulate the tif
file.
By loading the tif file in to a WIA.ImageFile and applying a WIA.Vector to it, you can then
itterate the pixels in the image and get the raw color values, by adding the values together
by column and taking into account that you have column's that are all white, these just being
a blank column I was able to generate a unique value per character.
Thanks for all your help.
Potman100