Methods to implement floor dirt detection algorithm

I'm trying to detect dirty floor areas in a series of images, using MATLAB and its Image Processing Toolbox, like the one that follows:

In the image above, there are two distinct areas, the whiter floor, which is considered clean, and the dirty floor, which is the area beyond the yellow warning sign. I'm looking for ways to detect these differences.

A relevant problem is that lighting intensity and colour may not be constant along the paths.

I've already tried 2D cross-correlation between a smaller sample image (taken from the image below), but it was not very effective.

My method was something like:

1. Mask out irrelevant features in input image (corridors other than the white ones, for example);

2. RGB to Grayscale conversion of input image (analysis target) and full sample image;

3. Extract a portion of the sample image and extract its histogram;

4. Use histogram equalization on input image, using the sample's histogram (histeq);

5. Run normxcorr2 between input and sample images;

6. Plot all points below an arbitrary constant (xCorr < 0.8, for example) over input image to detect "dirty" areas.

Maybe deep learning for image segmentation would be the most effective method, but I currently don't have the time to implement it.

Any other suggestions that would be any more effective on this situation?

• I can post the results on the cross-correlation test, other attempts I've made or the code itself, if they're any relevant for the question. Thanks! Commented Apr 23, 2018 at 16:35
• If you want to apply some modern tech to this problem, you could consider trying to use a convolution neural network with a training set of clean and dirty floor (sub)images to identify where portions of an image may be dirty. If you want something simpler, you could consider making a separate image by say coloring portions that are dirty in the original image with red pixels and portions that are clean with blue pixels. You could then feed the original image and marked image into some classification algo, like using Gaussian discriminants, and see how it does. Commented Apr 24, 2018 at 0:39
• How many labeled example pictures do you have? Are they in a public place we can contemplate them? Commented Nov 1, 2021 at 19:42