Very slow reading 1 bit-per-pixel BMP

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sanderton

Very slow reading 1 bit-per-pixel BMP

Post by sanderton »

Hello!
I've got some very large bitmap files (1 bpp), and the code seems awfully slow and convoluted. This is the code segment that just takes forever (from the ReadBMPImage() function in bmp.c):

Code: Select all

    switch (bmp_info.bits_per_pixel)
    {
      case 1:
      {
        /*
          Convert bitmap scanline.
        */
        for (y=(long) image->rows-1; y >= 0; y--)
        {
          p=pixels+(image->rows-y-1)*bytes_per_line;
          q=SetImagePixels(image,0,y,image->columns,1);
          if (q == (PixelPacket *) NULL)
            break;
          indexes=GetIndexes(image);
          for (x=0; x < ((long) image->columns-7); x+=8)
          {
            for (bit=0; bit < 8; bit++)
            {
              index=(IndexPacket) (((*p) & (0x80 >> bit)) != 0 ? 0x01 : 0x00);
              indexes[x+bit]=index;
              *q++=image->colormap[(long) index];
            }
            p++;
          }
          if ((image->columns % 8) != 0)
            {
              for (bit=0; bit < (image->columns % 8); bit++)
              {
                index=(IndexPacket) (((*p) & (0x80 >> bit)) != 0 ? 0x01 : 0x00);
                indexes[x+bit]=index;
                *q++=image->colormap[(long) index];
              }
              p++;
            }
          if (SyncImagePixels(image) == MagickFalse)
            break;
          if (image->previous == (Image *) NULL)
            if ((image->progress_monitor != (MagickProgressMonitor) NULL) &&
                (QuantumTick(y,image->rows) != MagickFalse))
              {
                status=image->progress_monitor(LoadImageTag,y,image->rows,
                  image->client_data);
                if (status == MagickFalse)
                  break;
              }
        }
        break;
      }
I'm curious to know why we need to make use of the indexes for an image that originally has only 1 bit per pixel. Couldn't this be made any faster?

My file has these details (from identify):
Image: C:\testing\BMP\DIB135.bmp
Format: BMP (Microsoft Windows bitmap image)
Class: PseudoClass
Geometry: 27543x14158+0+0
Type: Bilevel
Endianess: Undefined
Colorspace: Gray
Channel depth:
Gray: 1-bit
Channel statistics:
Gray:
Min: 0 (0)
Max: 1 (1)
Mean: 0.761977 (0.761977)
Standard deviation: 0.425873 (0.425873)
Colors: 2
Histogram:
92818039: #000000 black
297135755: #FFFFFF white
Colormap: 2
0: #000000 black
1: #FFFFFF white
Rendering intent: Undefined
Resolution: 28.34x28.34
Units: PixelsPerCentimeter
Filesize: 46.5014mb
Interlace: None
Background color: white
Border color: rgb(223,223,223)
Matte color: grey74
Transparent color: black
Page geometry: 27543x14158+0+0
Dispose: Undefined
Iterations: 0
Compression: Undefined
Orientation: Undefined
Signature: 818b67524accbaeec8646570dd052cf6b80661cc1ee45c6b218459f26929c686
Tainted: False
User time: 14.375u
Elapsed time: 6:34
Pixels per second: 1.11629mb
Version: ImageMagick 6.3.3 03/10/07 Q8 http://www.imagemagick.org

ftp://ftp.cadlink.com/pub/ImageMagick_/DIB135.bmp
Any ideas/help would be GREATLY appreciated!

Thanks,
sanderton

sanderton

Re: Very slow reading 1 bit-per-pixel BMP

Post by sanderton »

Hello Again!

Has anyone else had performance issues with 1 bpp BMP files?

Does anyone have any idea or suggestion on how this format can be made faster?

I've had to bypass all code that uses ImageMagick for this particular format, and use old code with other 3rd party libraries. I'd rather just use the IM library instead of having to use others too!

Thanks again,
sanderton

User avatar
magick
Site Admin
Posts: 11254
Joined: 2003-05-31T11:32:55-07:00

Re: Very slow reading 1 bit-per-pixel BMP

Post by magick »

You can find the answer to your questions in the ImageMagick architecture discussion. See http://magick.imagemagick.org/script/architecture.php.

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