Sort image files by average luminance and by average hue?

I'm not aware of anything in Aperture that provides this information. It's nothing I've ever seen either in the script hooks or within Aperture itself.

It would be something that would need to be computed by looking at the values in the image itself. Searching turns up a number of hits describing how to do it, such as Mean luminance Values of an Image - MathWorks but knowing the math and actually performing the operation on an image are two different things.

Perhaps with some further searching something might turn up

I'm working on a scripting tool that provides as part of its functionality access to Apple's CoreImage routines.

CoreImage has a area average filter that calculates the average value for each colour component (RGB space) of an image.

I can write a script that will get the average image colour value for your images. But I perceive a couple of problems.

How do you convert the RGB result to Luminance and Hue values? I don't know the math. Secondly there may be issues with color matching though I believe this is solvable.

If your interested let me know.

Kevin

Just had a quick look, there seems to be some fairly standard algorithms for converting from rgb to hsl, though I couldn't see anything that told me what rgb color profile those algorithms were using. I am assuming an equivalent of a core graphics generic linear rgb color space.

Though my scripting tool can be used from AppleScript I've written a library of methods using ruby to drive it. Ruby comes with OS X.

Kevin

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