aligning overlapping images and averaging the overlap

i have an empty matrix

canvas = uint8(zeros(10));

images are placed inside

image1=uint8(magic(3));

canvas(2:4,2:4)=image1;

a second image obviously overwrites the first

image2=uint8(magic(3));

canvas(3:5,3:5)=image2;

I would like to average the overlapping region

my attempt was to inspect each element in canvas to see if it was zero or non zero and then average each element(of subsequent images) one by one if it was non zero. sadly my code is really slow and doesn't work properly..

please help

Answer 1

[David Young]

I'm not quite sure what you want to do in the non-overlapping region, but if you want to leave the original images as they are, then you can do it like this:

canvas1 = uint8(zeros(10));
canvas2 = canvas1;

image1=uint8(magic(3));
canvas1(2:4,2:4)=image1;

image2=uint8(magic(3));
canvas2(3:5,3:5)=image2;

canvas = canvas1 + canvas2;
overlap = canvas1 & canvas2;

canvas(overlap) = canvas(overlap)/2;

I don't think this corresponds exactly to your code though. If you could say what the result in your example should be, it would be possible to be more certain of what to do.

[james]

this does what i want, it should be much faster than the for loops.

thank you

[David Young]

Just a thought - using uint8 for all the arithmetic might cause you problems. For example, it will mean that no value in the overlapping region can exceed 128. It might be wise to do all the arithmetic in floating point, if possible, and convert back to uint8 when definitely need the image in that format.

Answer 2

[james]

this method doesn't work..

canvas = uint8(zeros(10));

image1=uint8(magic(3));
image2=uint8(magic(3));

canvas(2:4,2:4)=image1;

for rowcounter=1:3;
    for colcounter=1:3;
        if canvas(rowcounter,colcounter)==0;
          canvas(2+rowcounter,2+colcounter)=image2(rowcounter,colcounter);
          elseif canvas(rowcounter,colcounter)~=0;            
              canvas(2+rowcounter,2+colcounter)=((canvas(2+rowcounter,2+colcounter))+(image2(rowcounter,colcounter)))/2;
          end
      end
  end

    image(canvas)

Answer 3

[Sean de Wolski]

To start: -use CONV2 with a ones kernel to figure out how many zeros are touching.

[james]

can you put that in the context of the ^^ code?

[Sean de Wolski]

No, since your above code "doesn't work" for you. I would guess what is wrong with your above code is that you're updating things and then checking the updates but I don't really know. CONV will do the averaging for you; you can use logical indexing to find if an element is zero. I don't totally understand what you're trying to do though, so more explanation would be better.

Answer 4

[james]

this works, could it be faster?

canvas = uint8(zeros(10));

image1=uint8(magic(3));
image2=uint8(magic(3));

canvas(2:4,2:4)=image1;

for rowcounter=1:3;
    for colcounter=1:3;
        if canvas(2+rowcounter,2+colcounter)==0;
            canvas(2+rowcounter,2+colcounter)=image2(rowcounter,colcounter);
        end
        if canvas(2+rowcounter,2+colcounter)~=0;
            canvas(2+rowcounter,2+colcounter)=((canvas(2+rowcounter,2+colcounter))+(image2(rowcounter,colcounter)))/2;
        end
    end
end

image(canvas);

[Sean de Wolski]

You do realize that the it will add image2 twice since you're using two if statements not an else-if statement right?

[james]

never assume! no i didn't realise thanks.