Why B44 compression does not reduce size of exr image?

[Shantanu Daithankar]

Hi,

I am trying play a bunch of frames as a video and for which I plan to use
the exr format for the frames. For doing the same I am using ImageMagick to
convert a set of dpx images to B44 compressed exr images. The problem is
that the dpx images do get converted to exr format, but the compression does
not happen in spite of specifying it with the appropriate command and the
size of the image remains massive( DPX - 8.1 MB to EXR - 21.7 MB ). Even
after performing only the conversion and without compression option
specified, the size of the image is still 21.7 MB so I figured that the
compression is not taking place even when its specified and after its error
free execution.

My question is why are the images not getting compressed even when the
compression scheme is specified? And is it normal and correct for the images
to expand this much in size when the conversion of format takes place from
dpx to exr. The image quality also seems to be very poor for the converted
exr's.

Below are the commands that I am using to convert and compress:

mogrify -format exr *.dpx -compress B44

Any help on this will be appreciated and if its in terms of literal commands
it will be even better.


Shantanu

[Fred Weinhaus]

try putting the output images last

mogrify -format exr -compress B44 *.dpx

[Fred Weinhaus]

I don't know that IM knows about B44 compression. See -compress
options at
http://www.imagemagick.org/script/command-line-options.php?ImageMagick=v5p6ppe4aoaliql9pk4nv603k2#compress