crop_borders.m

function [A, vA, vB, bb_rel] = crop_borders(A, bcol, padding)
%CROP_BORDERS Crop the borders of an image or stack of images
%
%   [B, vA, vB, bb_rel] = crop_borders(A, bcol, [padding])
%
%IN:
%   A - HxWxCxN stack of images.
%   bcol - Cx1 background colour vector.
%   padding - scalar indicating how much padding to have in relation to
%             the cropped-image-size (0<=padding<=1). Default: 0
%
%OUT:
%   B - JxKxCxN cropped stack of images.
%   vA     - coordinates in A that contain the cropped image
%   vB     - coordinates in B where the cropped version of A is placed
%   bb_rel - relative bounding box (used for eps-cropping)

% 06/03/15: Improved image cropping thanks to Oscar Hartogensis

    if nargin < 3
        padding = 0;
    end
    [h, w, c, n] = size(A);
    if isscalar(bcol)
        bcol = bcol(ones(c, 1));
    end
    bail = false;
    for l = 1:w
        for a = 1:c
            if ~all(col(A(:,l,a,:)) == bcol(a))
                bail = true;
                break;
            end
        end
        if bail
            break;
        end
    end
    bcol = A(ceil(end/2),w,:,1);
    bail = false;
    for r = w:-1:l
        for a = 1:c
            if ~all(col(A(:,r,a,:)) == bcol(a))
                bail = true;
                break;
            end
        end
        if bail
            break;
        end
    end
    bcol = A(1,ceil(end/2),:,1);
    bail = false;
    for t = 1:h
        for a = 1:c
            if ~all(col(A(t,:,a,:)) == bcol(a))
                bail = true;
                break;
            end
        end
        if bail
            break;
        end
    end
    bcol = A(h,ceil(end/2),:,1);
    bail = false;
    for b = h:-1:t
        for a = 1:c
            if ~all(col(A(b,:,a,:)) == bcol(a))
                bail = true;
                break;
            end
        end
        if bail
            break;
        end
    end

    % Crop the background, leaving one boundary pixel to avoid bleeding on resize
    %v = [max(t-padding, 1) min(b+padding, h) max(l-padding, 1) min(r+padding, w)];
    %A = A(v(1):v(2),v(3):v(4),:,:);
    if padding == 0  % no padding
        padding = 1;
    elseif abs(padding) < 1  % pad value is a relative fraction of image size
        padding = sign(padding)*round(mean([b-t r-l])*abs(padding)); % ADJUST PADDING
    else  % pad value is in units of 1/72" points
        padding = round(padding);  % fix cases of non-integer pad value
    end

    if padding > 0  % extra padding
        % Create an empty image, containing the background color, that has the
        % cropped image size plus the padded border
        B = repmat(bcol,(b-t)+1+padding*2,(r-l)+1+padding*2);
        % vA - coordinates in A that contain the cropped image
        vA = [t b l r];
        % vB - coordinates in B where the cropped version of A will be placed
        vB = [padding+1, (b-t)+1+padding, padding+1, (r-l)+1+padding];
        % Place the original image in the empty image
        B(vB(1):vB(2), vB(3):vB(4), :) = A(vA(1):vA(2), vA(3):vA(4), :);
        A = B;
    else  % extra cropping
        vA = [t-padding b+padding l-padding r+padding];
        A = A(vA(1):vA(2), vA(3):vA(4), :);
        vB = [NaN NaN NaN NaN];
    end

    % For EPS cropping, determine the relative BoundingBox - bb_rel
    bb_rel = [l-1 h-b-1 r+1 h-t+1]./[w h w h];
end

function A = col(A)
    A = A(:);
end