Sort image files by average luminance and by average hue?

Question

Hi.  I would like to be able to sort images by average luminance and by average hue.  Is there anything in OS X that will let me determine the average luminance or average hue of an image, and save that datum to the image?
Ultimately, I would like to use this within Aperture (my sole area of expertise {all my ASC points are from the Aperture forum}).  After I posted the question there, a regular suggested I post in this forum to find out what is possible:  specifically, are there any AppleScript hooks that might allow this?  (Sadly, I don't script, but it helps me know what can be done.)
I know of one program which does this: CF/X's Photo Mosaic, which uses the averages to match an image to a tile in the "master image".  I don't know of any way to attach the Photo-Mosaic-generated averages to the files themselves.  I asked CF/X about this today.
Thanks.

Answer 1

Hello
You may try the AppleScript script listed below. It is a simple wrapper of rubycocoa script which uses CIFilter to calculate average brightness and hue of each image (jpg|jpeg|png) in specified directory tree. It is a skeleton just to generate a TSV output of [brightness, hue, file] records sorted by brightness and then hue on desktop. I don't know how to embed these info into image metabata.
Script is briefly tested under 10.6.8.
Hope this may help somehow,
H
PS. If copied code has extra spaces in front of every line, which appears to be the case with some browsers including Firefox, please remove them before running the script.
-- SCRIPT
set d to (choose folder with prompt "Choose start folder")
set args to d's POSIX path's quoted form
do shell script "/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby -w <<'EOF' - " & args & " > ~/desktop/test_out.txt
#     get average brightness and hue of image files (jpg|jpeg|png)
#     * output record = B=brightness [TAB] H=hue [TAB] file [LF]
#     * sorted by brightness and then hue
require 'osx/cocoa'
include OSX
EXTS = %w[ jpg jpeg png ]    # target extensions
module OSX
    class << CIContext
        def contextWithSize(w, h)
            br = NSBitmapImageRep.alloc.objc_send(
                :initWithBitmapDataPlanes, nil,
                :pixelsWide, w,
                :pixelsHigh, h,
                :bitsPerSample, 8,
                :samplesPerPixel, 4,
                :hasAlpha, true,
                :isPlanar, false,
                :colorSpaceName, NSCalibratedRGBColorSpace,
                :bytesPerRow, 0,
                :bitsPerPixel, 0)
            c = NSGraphicsContext.graphicsContextWithBitmapImageRep(br)
            CIContext.objc_send(:contextWithCGContext, c.graphicsPort , :options, {})
        end
    end
    class CIFilter
        def setParameters(dict)
            self.setValuesForKeysWithDictionary(dict)
        end
        def output
            self.valueForKey('outputImage')
        end
    end
    class << CIVector
        def vectorWithRect(r)
            self.vectorWithX_Y_Z_W(r.origin.x, r.origin.y, r.size.width, r.size.height)
        end
    end
end
# process ARGV and retrieve image files with given extensions under specfied directory
raise ArgumentError, %Q[Usage: #{File.basename($0)} directory] unless ARGV.length == 1
dir, = ARGV.map { |a| a == '/' ? a : a.chomp('/')}
ff = %x[find -E \"#{dir}\" -type f -iregex '.*/.*\\.(#{EXTS.join('|')})$' -print0].split(/\\0/)
# get CIContext and CIFilter
cic = CIContext.contextWithSize(5000, 5000)  # let it be large enough
cif = CIFilter.filterWithName('CIAreaAverage')
cif.setDefaults
# retrieve average brightness and hue of images
hh = {}
ff.each do |f|
    u = NSURL.fileURLWithPath(f)
    ci = CIImage.imageWithContentsOfURL(u)
    civ = CIVector.vectorWithRect(ci.extent)
    cif.setParameters({'inputImage' => ci, 'inputExtent' => civ})
    ciout = cif.output
    cgout = cic.objc_send(:createCGImage, ciout, :fromRect, ciout.extent)
    colr = NSBitmapImageRep.alloc.initWithCGImage(cgout).colorAtX_y(0, 0)
    hh[f] = { :b => colr.brightnessComponent, :h => colr.hueComponent}
end
# sort criteria
brightness          = lambda { |k| hh[k][:b] }
hue                 = lambda { |k| hh[k][:h] }
brightness_and_hue  = lambda { |k| b, h = hh[k].values_at(:b, :h); b * 1e6 + h }
# print sorted records
hh.keys.sort_by(&brightness_and_hue).each do |k|
    b, h = hh[k].values_at(:b, :h)
    puts %Q[B=%f\\tH=%f\\t%s] %  [b, h, k]
end
EOF"
-- END OF SCRIPT