Read an image pixel by pixel in Ruby

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, GI开发者_C百科F 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?

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

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.

If you are only opening the file to display the bytes, and don't need to manipulate it as an image, then it's a simple process of opening the file like any other, reading X number of bytes, then iterating over them. Something like:

File.open('path/to/image.file', 'rb') do |fi|
  byte_block = fi.read(1024)
  byte_block.each_byte do |b|
    puts b.asc
  end 
end

That will merely output bytes as decimal. You'll want to look at the byte values and build up RGB values to determine colors, so maybe using each_slice(3) and reading in multiples of 3 bytes will help.

Various image formats contain differing header and trailing blocks used to store information about the image, data format and EXIF information for the capturing device, depending on the type. Probably going with a something that is uncompressed would be good if you are going to read a file and output the bytes directly, such as uncompressed TIFF. Once you've decided on that you can jump into the file to skip headers if you want, or just read those too to see or learn what's in them. Wikipedia's Image file formats page is a good jumping off place for more info on the various formats available.

If you only want to see the image data then one of the high-level libraries will help as they have interfaces to grab particular sections of the image. But, actually accessing the bytes isn't hard, nor is it to jump around.

If you want to learn more about the EXIF block, used to describe a lot of different vendor's Jpeg and TIFF formats ExifTool can be handy. It's written in Perl so you can look at how the code works. The docs nicely show the header blocks and fields, and you can read/write values using the app.

I'm in the process of testing a new router so I haven't had a chance to test that code, but it should be close. I'll check it in a bit and update the answer if that didn't work.