Read an image pixel by pixel in Ruby

Question

I'm trying to open an image file and store a list of pixels by color in a variable/array so I can output them one by one.

Image type: Could be BMP, JPG, GIF or PNG. Any of them is fine and only one needs to be supported. Color Output: RGB or Hex.

I've looked at a couple libraries (RMagick, Quick_Magick, Mini_Magick, etc) and they all seem like overkill. Heroku also has some sort of difficulties with ImageMagick and my tests don't run. My application is in Sinatra.

Any suggestions?

Answer 1

You can use Rmagick's each_pixel method for this. each_pixel receives a block. For each pixel, the block is passed the pixel, the column number and the row number of the pixel. It iterates over the pixels from left-to-right and top-to-bottom.

So something like:

pixels = []

img.each_pixel do |pixel, c, r|
    pixels.push(pixel)
end
# pixels now contains each individual pixel of img

Answer 2

I think Chunky PNG should do it for you. It's pure ruby, reasonably lightweight, memory efficient, and provides access to pixel data as well as image metadata.