Retrieve the pixel values of an image with Haskell

Question

Is there a way or a library available that can load an image (jpeg, png, etc) and assign the pixel values of that image into a list or matrix? I'd like to do some experiments with image and pattern recognition.

A little nudge in the right direction would be appreciated.

score 4 · Answer 1 · answered Oct 15 '12 at 19:10

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You can use JuicyPixels, a native Haskell library for image loading. This is rather easy to convert to REPA as well (manually or with JuicyPixesl-repa).

answered Oct 15 '12 at 19:10

Thomas M. DuBuisson

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Thomas, would you happen to know where I could find some usage examples? The documentation is reading very cryptically for me. – subtlearray Jun 02 '13 at 00:36
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I can't help much without knowing the task. I suggest starting with `func file = onImg someRepaFunction \`fmap\` readImage file`. Using that line you should only need to define `someRepaFunction`. – Thomas M. DuBuisson Jun 02 '13 at 00:47
I'm sorry for bothering you. I don't know what a repa is, and I can't get repa-devil to install in Windows because of some -dev C library dependency. My patience has finally ran out. I like Haskell, but I can't deal with this anymore. Thank you again for your time. – subtlearray Jun 02 '13 at 01:45
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Repa is an array library, there are tutorials you can find online - one linked in the below answer. If you are looking for more real-time help then I suggest you try IRC (#haskell on freenode.net) – Thomas M. DuBuisson Jun 02 '13 at 01:50

score 3 · Answer 2 · answered Oct 15 '12 at 18:52

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Try the repa library .Also there is a small tutorial here

answered Oct 15 '12 at 18:52

user1105045

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Very helpful tutorial. I've saved it for offline viewing. Thank you. – subtlearray Oct 19 '12 at 21:04

score 3 · Accepted Answer · answered Oct 15 '12 at 19:09

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I've used the repa-devil package for this in the past. It lets you work with a bunch of formats using Developer's Image Library (DevIL). You can read and write all the formats you are likely to care about.

The actual image data is given as a Repa array. This is a great library for array operations and makes it very easy to write parallel code.

answered Oct 15 '12 at 19:09

Tikhon Jelvis

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Just a note to self (and others): The "Missing C library: IL" is likely libdevil-dev. – subtlearray Nov 23 '12 at 21:34

score 1 · Answer 4 · answered Apr 17 '16 at 08:24

Here is a new Haskell Image Processing library, which uses JuicyPixels for encoding, provides interface for you to read and write all of the supported formats in a very easy manner and manipulate them in any way you can imagine. Just as a simple example on how easy it is:

>>> img <- readImageRGB "image.jpg"
>>> writeImage "image90.png" $ rotate90 img

Above will read a JPG image in RGB color space, rotate it 90 degrees clockwise and save it as a PNG image.

Oh yeah, it also can use Repa, so you will get parallel processing for free as well.

score 0 · Answer 5 · answered Oct 15 '12 at 19:07

GTK supports loading and saving JPEG and PNG. [AFAIK, no other formats though.] There is a Haskell binding named Gtk2hs. It supports vector graphics very well, but bitmap graphics, while supported, isn't especially easy to figure out. So I wrote AC-EasyRaster-GTK, which wraps GTK in a more friendly interface. (It still needs Gtk2hs though.) The only real down-side is that Gtk2h is a bit fiddly to set up on Windows. (And it's arguably overkill to install an entire GUI toolkit just to load and save image files.)
I gather the "GD" library supports writing several image formats, and is quite small and simple. I believe Hackage has Haskell bindings for GD as well. I haven't tried this personally.
There is a file format called PPM which is deliberately designed to be ridiculously easy to implement (it's a tiny header and then an array of pixels), and consequently there's at least a dozen packages on Hackage which implement it (including my own AC-PPM). There are also lots of programs out there which can display and/or convert images in this format.

Retrieve the pixel values of an image with Haskell

5 Answers5