How to color an image according to orientation of objects?

I use the following code:

I = imread(picture);
BW = imbinarize(rgb2gray(I));
figure()
h = imshow(BW); 
axis on
props = regionprops(BW, 'Orientation');
allAngles = [props.Orientation];
histogram(allAngles);

to get orientation histogram of all the objects on an image.

How can I get an image with orientations assigned for all the objects?

The following code seems not to work properly:

y= ismember(BW,find([props.Orientation]));
imagesc(BW+y )
title('Objects according to their orientations')
colormap()

As it shows only 2 colors, not the entire orientation spectrum.

I know it's probably like taking candy from a baby, but I'm a Matlab newbie.

Answer 1

[Walter Roberson]

When you regionprops(), also ask for PixelIdxList .

Now, create a matrix

orient = zeros(size(BW));

And loop through the struct array you got from regionprops:

orient(props(K).PixelIdxList) = props(K).orientation;

After this you can imshow() or imagesc() orient .

Note that very high orientations and very low orientations are close to each other, so you might want to use an hsv colormap or something similar that is "circular"

[youl]

clear all;clc
I = imread('picture.png');
BW = imbinarize(rgb2gray(I));
figure()
h = imshow(BW); 
axis on
props = regionprops(BW, 'Orientation','PixelIdxList');
allAngles = [props.Orientation];
histogram(allAngles);
orient = zeros(size(BW));
    for k = 1 : length(props)
    y=props(k).PixelIdxList;
    orient(y) = props(k).Orientation;
    end
imagesc(BW+orient )
title('Objects according to their orientations')
colormap()

Like that? It's looking pretty decent now, but I just want to make sure

[Walter Roberson]

That looks okay. I might be tempted, though, to use

h = imagesc(y, [0 360]);
h.AlphaData = double(BW);

Providing the range permits you to compare image to image, in case some do not have as high maximum orientation as others. Using AlphaData that particular way makes the orientation image transparent where there are no objects.

[Walter Roberson]

That would replace

imagesc(BW+orient )

[Image Analyst]

How about you upload your picture so we can actually try it and see rather than guessing?