Convert file to 24bit bitmap

imagemagick

I'm using imagemagick convert to convert this image http://i.imgur.com/P1uqj9K.jpg to a bmp. However for some reason the tool I am using doesn't like the bitmap. If I save the image as a png and convert it to a 24bit bmp its fine. I tried using the following command bit it doesn't like it.

convert -verbose  -depth 8 -type truecolor infile outfile.bmp

Looking at the file I see that the 'bad' bmp has

BMÊp1 (0's) Š

The good one has

BMvp1 (0's) 6

Best Answer

I have had some trouble with BMP conversions too. I have typically specified BMP3:outfile.bmp and I normally get 24 bit BMP files. sometimes I get an 8 bit BMP when converting JPEG files. I just tried the -type truecolor (having seen it here) and now it looks like I get a 24 bit BMP in the cases where I used to get only 8 bits.

I also use these switches:

-units PixelsPerInch -density 72 -compress None -depth 24

the -depth 24 should do a 24 bit BMP (the depth -8 in your case may also be causing a problem) but as I said I sometimes get 8 bits even with the 24 specified.

the -units and -density cases corrected a problem where sometimes I would get a 0 for the biXPelsPerMeter and biYPelsPerMeter fields in the BMP header (it did not seem to cause a problem though). by the way I have not found a good explanation of these 2 fields.

the -compress None was required because sometimes a conversion generated a compressed BMP - no logical reason for doing that was found.

hopefully this will be of some help but I am not an expert on this subject - I just tried a few things and looked around using Google and came up with the above switch settings.

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Bulk convert PNG-24 to PNG-8 files with best quality

pngquant is exactly the tool for this. It generates palettes better than ImageMagick.

pngquant --quality=0-90 *.png

This will convert all png files in current directory, and automatically choose number of colors to achieve quality similar to 90%-quality JPEG.

(if it doesn't accept the --quality switch it means you have terribly outdated low-quality version and you should upgrade).

Linux – How to convert DICOM images to PNG

It looks like you're trying to convert at 16-bit image to 8-bit. It looks like a CT image, where pixel values typically go from -1000 (air) to 0 (water) to 3000 (dense bone).

I'm guessing the PBM program is mapping the 16-bit to 8-bit by rescaling the pixel values. It looks like the PNM version is only taking the lower 8-bits and ignoring the upper 8. The PNG image probably has the entire 16 bit data, since PNG supports it, but your viewer displays only the upper 8-bits, ignoring the lower 8.

You need to rescale the pixel intensities to 0-255 from -32768-32767 (or 0 to 63356 if you view them as unsigned 16 bit ints).

You can do this using SimpleITK in Python like so:

import SimpleITK as sitk

img = sitk.ReadImage("000005.dcm")
# rescale intensity range from [-1000,1000] to [0,255]
img = sitk.IntensityWindowing(img, -1000, 1000, 0, 255)
# convert 16-bit pixels to 8-bit
img = sitk.Cast(img, sitk.sitkUInt8)

sitk.WriteImage(img, "000005.png")

Best Answer

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Bulk convert PNG-24 to PNG-8 files with best quality

Linux – How to convert DICOM images to PNG

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