crop.m

function crop(filename, eye0, eye1, top, left, dsize)
	%% Rotates an image around the eyes, resizes to destination size.
	%%
	%% Assumes a filename is structured as ".../subject/image.extension", so that
	%% images are saved in a the folder (relative to where you call the script):
	%% 	"crop_<subject>/crop_<filename>"
	%%
	%% Args:
	%%	filename: Image to preprocess.
	%%	eye0: [x,y] position of the left eye
	%%	eye1: [x,y] position of the right eye
	%%	top: percentage of offset above the eyes
	%%	left: percentage of horizontal offset 
	%%	dsize: [width, height] of destination filesize
	%%
	%% Example:
	%% crop("/path/to/file", [300, 100], [380, 110], 0.3, 0.2, [70,70])
	%% 
	%% Leaves 21px offset above the eyes (0.3*70px) and 28px horizontal
	%% offset. 20% of the image to the left eye, 20% to the right eye
	%% (2*0.2*70=28px).
	
	basename = sprintf("%s",strsplit(strsplit(filename, filesep){end}, "."){:})
	subject = ["crop_",strsplit(filename, filesep){end - 1}]
	
	% create folder if necessary
	if ~isdir(subject)
		mkdir(subject)
	end
	
	% pixel in original image
	vOffset = floor(top*dsize(2))
	hOffset = floor(left*dsize(1))

	eye2 = eye1 - eye0

	% rotation angle to align both eyes
	rotation = -atand(eye2(2)/eye2(1))

	% distance between them
	dist = sqrt(sum(((eye0-eye1).^2),2))
	
	% calculate reference eye-width
	reference = dsize(1) - 2*hOffset
	
	scale = dist/reference

	%% scale offsets
	cropX = eye0(1) - scale*hOffset;
	cropY = eye0(2) - scale*vOffset;
	
	% geometry string for ImageMagick crop 
	crop0 = sprintf("%dx%d+%d+%d", dsize(1)*scale, dsize(2)*scale, cropX, cropY)
	
	tmpfn = "tmp.png";
	outfn = [subject, filesep, "crop_", basename, ".png"];
	
	% rotate around left eye (http://www.imagemagick.org/script/command-line-options.php?#distort)
	cmd0 = sprintf("convert %s +distort ScaleRotateTranslate '%d,%d %d' %s", filename, eye0(1), eye0(2), rotation, tmpfn)
	% crop (http://www.imagemagick.org/script/command-line-options.php?#crop) and resize (http://www.imagemagick.org/script/command-line-options.php?#resize)
	cmd1 = sprintf("convert %s -crop %s -resize %dx%d! %s", tmpfn, crop0, dsize(1), dsize(2), outfn)
	
	% ... and now let the ImageMagick happen!
	system(cmd0);
	system(cmd1);
	
	% do cleanup
	system(sprintf("rm %s", tmpfn))
end