Remove shadows from an image as a form of preprocessing

[Oluwatoni]

Given an image of the track remove the shadows in that image

Acceptance Criteria
Inputs

• Left/Right camera stream

Outputs

• Image without shadows

Code should be fast enough to run realtime(30Hz)

[TranBrian10]

Implementing the shadow removal process found in: "Shadow Detection and Removal from a Single Image
Using LAB Color Space".

[Oluwatoni]

Deadline: 17th of MAy for MATLAB and 24th for Opencv

[TranBrian10]

Test image 1. Works well with default parameters.

THRESHOLD_TOLERANCE = 0.8;
MIN_SHADOW_AREA = 30;
MASK_DILATION = 6;
EXPANDED_SHADOW_MASK_DILATION = 10;
EXPANDED_EDGE_MASK_DILATION = 8;
MED_FILTER_KERNEL_SIZE = 15;

[TranBrian10]

Test image 2. Had to change THRESHOLD_TOLERANCE to 1.5 and MASK_DILATION to 8 to get it to detect shadows. Lines look pretty good before the over-illumination fix, but then get a little messed up because the shadows are pretty spotty (the over-illumination fix applies to edges of shadows). Still, the white lane lines are mostly visible and it's better than detecting no lane lines at all. This is probably the most difficult test image because the majority of the road is covered by spotty shadows.

[TranBrian10]

Test image 3. Had to change THRESHOLD_TOLERANCE to 1. Not much to say here since the shadows don't overlap the lane lines. The "Removed Shadows" stage looks pretty artsy though.

[TranBrian10]

Test image 4. Had to change THRESHOLD_TOLERANCE up to 1.5 since the original image had horribly blown out highlights. Didn't go too well, but this is a very non-ideal image and half the frame is pretty much white anyways.

[TranBrian10]

Test image 5. Works decently well with default parameters. Blurs some of the dotted white lane lines in the distance, but those probably wouldn't be in the region of interest anyways. More importantly, the lane line in the right foreground is brought out of shadow.

[TranBrian10]

Test image 6. Had to change THRESHOLD_TOLERANCE to 1.2 and MASK_DILATION to 8. Great results with the lane line in the foreground, although it cuts a bit off the top of the line with the over-illumination step. I could see this being an issue if a shadow just borders a lane line and the over-illumination fix runs the median filter over the line and erases it.

[TranBrian10]

Test image 7. Works well with default values. Not much to say here - the shadows don't cover the lane lines and the algorithm does its job.

[TranBrian10]

Test image 8. Had to change THRESHOLD_TOLERANCE to 1.2. Shadows don't overlap the lane lines here, and the white and yellow lane lines are mostly intact. However, the over-illumination step wipes out the second-nearest white dotted lane line, which is a bummer, but it's a very small part of the image (not sure if it would be picked up by the lane detection).