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I've been working with ImageMagick on the Raspberry Pi (model B) and have noticed a bottle neck in the area of image conversions.

When converting between bmp, jpg, png, etc. the speeds are acceptable but I also have a need to convert RAW formats.

In particular, I have been converting NEF to jpg at 70% for benchmark tests.

The Raspberry Pi takes just over 5 minutes to convert a single 12.7 MB image compared with 14 seconds on my Ubuntu Laptop.

Of course, I understand the limitations of the Pi's hardware but I am very interested in how I can really get the most from the performance.

I already know about overclocking and intend to implement this tomorrow when I work on it next.

Information:

  • Raspberry Pi uses heavily modified version of Raspbian (lightweight, no X, unnecessary software stripped out, running Apache, running own software)
  • A class 10 4GB SD card is used
  • Benchmarks taken without overclocking
  • Totally headless

Some things I am considering:

  • Overclocking

  • Finding another piece of software which may be able to perform conversions on raw faster

  • Trying to find a way to utilise the GPU as well as the CPU (possibly forking the necessary code for conversions and attempting modifications to use GPU)

  • Allocating all possible RAM to CPU

Any help is greatly appreciated, whether it be advice on optimisations or another piece of software that could be used.

I don't expect it to be as fast as a laptop but ideally the speed would increase to around 1 - 2 minutes per image.

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Five minutes? You sure are doing something wrong (or are using some CPU-intensive options that you haven't told us about). For me, the command

gm convert -quality 70 DSC_1432.NEF DSC_1432.jpg

takes 53 s on a stock Raspberry Pi. The image is a 12 MB, 12 mpx file from my Nikon D90.

A quicker, simpler workflow is to use a pipeline of two simple command line tools, dcraw and cjpeg, which you can install like this:

sudo apt-get install dcraw libjpeg-progs

and run like:

dcraw -c DSC_1432.NEF | cjpeg -qual 70 > DSC_1432.jpg

This takes 50 s on my Raspberry Pi.

If you're willing to sacrifice some image quality (and if you're batch-converting RAW→JPEG without some knowledge of the contents, you're probably not too fussed about the JPEG quality), this is much faster still:

dcraw -q 0 -c DSC_1432.NEF | cjpeg -qual 70 > DSC_1432.jpg

This converts an image in 24 s.

Fastest of all — but resulting in a half-sized output image — is:

dcraw -h -c DSC_1432.NEF | cjpeg -dct fast -qual 70 > DSC_1432.jpg

This converts an image in just 9 s.

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  • This works fantastically, thank you. I was using imagemagick instead but I have no idea what was causing the slow down. Your solutions work nicely!
    – Arcana
    Aug 7, 2014 at 9:56
  • Ah, now that I try ‘real’ ImageMagick, it takes about four minutes for the first example. I'd assumed that Raspbian was like Ubuntu, where ImageMagick had been replaced by the more open-source-friendly GraphicsMagick fork. But seemingly, no.
    – scruss
    Aug 7, 2014 at 12:01

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