Convert PNG to 8-Bit Palette BMP

[nm-osm]

The PNG has 31 colors as reported from totalColors(). My code is:

Code: Select all

// img has a type with const char *data() and size_t length()
Magick::Blob inblob( img.data(), img.length() );
Magick::Image image;
image.read( inblob );
image.compressType( MagickCore::NoCompression );
image.type( MagickCore::PaletteType );
image.colorMapSize( 256 );
Magick::Blob outblob;
image.write( &outblob, "bmp3" );

The resulting image is barely visible, the colors are reduced to a dark grey. The CLI-tool convert works OK.

• $ convert x.png -type Palette -depth 8 -compress none bmp3:x.bmp

I have tried with various combinations of

• image.quantizeColors( 256 )
  image.depth( 8 )
  image.depth( 24 )
  image.classType( MagickCore::DirectClass )
  image.classType( MagickCore::PseudoClass )
  image.colorSpace( MagickCore::sRGBColorspace )
  image.colorspaceType( MagickCore::sRGBColorspace )
  image.quantize()

Has anyone an idea how to transfer the 31 colors from the PNR into the colormap with fidelity?

TIA

[fmw42]

I would suggest you provide your version of IM and platform and also post your PNG image so others can test using the command line.

[nm-osm]

The version is ImageMagick-6.9.1-1, platform is SUSE Linux Enterprise Server 11.

How do I post an image? I have seen images posted by others but not found a way to do it myself . There is no button to add an attachment.

[fmw42]

You must post to some free service such as dropbox.com and then put the URL here.

[nm-osm]

I have put the pictures on flickr:

imagemagick-input.png = https://www.flickr.com/photos/132066708 ... 310395011/
imagemagick-output.bmp = https://www.flickr.com/photos/132066708 ... 103444757/

Sorry about the delay but I was on vacation the last days.

[fmw42]

This seems to work for me on IM 6.9.1.3 Q16 Mac OSX in the command line.

Note your png file has a totally opaque alpha channel which I removed.

Code: Select all

convert 17310395011_f1a497f25f_o.png -alpha off -type palette BMP3:17310395011_f1a497f25f_o.bmp

Sorry, I do not know the Magick++ API equivalent.

[nm-osm]

As I wrote it's works for me on the command-line too. The problem is with the C++-API.

[nm-osm]

We have ceased to use IM for this -> problem solved.

[cuongvn08]

We have ceased to use IM for this -> problem solved.

I also have same problem as your issue. I would like to convert the original image to 8-bit palette bmp.
I am thinking to stop using IM and change to another library. My programming platform is Ubuntu, php.
So what is the library you are using now?
And how can you fix this issue.
Thanks.

[fmw42]

If it works from the command line, then there should be an equivalent for Magick++. Did you try prefacing your output image with BMP3:output.bmp? Sorry, I do not know Magick++, but someone should be able to help.

[nm-osm]

So what is the library you are using now?

Sorry, no library. We convert the pictures with an external script before the c++ program has to handle them.