How to Extract a certain Shape from Image

I would like to distinguish between "background" pixels and the "orange plastic bag" pixels in order to manipulate those pixels (count, hist, etc).

I can't use indx = I(I ~= 1) because there are some white pixel inside the orange plastic bag.

Moreover, this bag is aligned but it might be rotate in other images.

Thanks.

Image URL: http://snag.gy/tk7kH.jpg

[Rakshit Kothari]

So what you basically need is some form of object recognition, am i correct? If you just need to extract the bag of chips, image segmentation using Otsu's method is probably what you need.

If you need recognition i suggest you read up on SIFT or SURF.

Answer 1

[Walter Roberson]

convert to gray, threshold to select non-white, imfill() 'holes'. The result should be a mask you can use to select from the larger image.

[Max]

it is a problematic since I can't use indx = I(I ~= 1) because there are some white pixel inside the orange plastic bag.

[Walter Roberson]

That's why you imfill() 'holes', to recover the "inside" part.

Answer 2

[Rakshit Kothari]

So what you basically need is some form of object recognition, am i correct? If you just need to extract the bag of chips, image segmentation using Otsu's method is probably what you need.

If you need recognition i suggest you read up on SIFT or SURF.

If its a quick thing that you are looking for, just invert the image, threshold and then use REGIONPROPS with filled holes option.

If you need the shape of the object:

Ratio = Area of Object/Area under bounding box

If Ratio is a reasonably high value, you object is a square or a rectangle. If its lower, its probably a triangle or circle.

[Darshan Drviruz]

Would you please explain this by using code? i couldn't understand well