Crop image by removing edges with homogeneous intensity

Crop image by removing edges with homogeneous intensity and leaving a specified width

USAGE
img2 = crop_img(img)
img2 = crop_img(img,border)

INPUT
- IMG: MxNxC matrix, where MxN is the size of the image and C is the number of color layers
- BORDER: maximum number of pixels at the borders

OUPUT
- IMG2: cropped image

EXAMPLE
>> img = imread('my_pic.png');
>> img2 = crop_img(img,0);
>> imwrite(img2,'my_cropped_pic.png')