PLY/ RGB to 2D Grayscale Image

I have a PLY from a stereo vision sensor (1024 x 1280). The PLY gives:

- Location (X,Y,Z) [1310442 x 3]

- Color (R, G, B) [1310442 x 3] and

- XLimits, YLimits, ZLimits.

I am trying to convert the Color into a grayscale image/matrix. My attempt has been the following:

Image = ptCloud.Color(:,:,1);
R = double(Image(:,1));
G = double(Image(:,2));
B = double(Image(:,3));

I = 0.2989 * R + 0.5870 * G + 0.1140 * B; % For grayscale

%
% Since the matrix size does not equal 1024 x 1280, I add zeros to the end of I to compensate
%

Image_2d = reshape (I, 1024, 1280)

The image on the left is by plotting the PLY with MatLab's pcshow feature. This is what I want to obtain as an image/matrix but instead by following the above code... I get the image on the right which does not look correct!

Answer 1

[Rohit Pappu]

Based on the above code,

• Image stores the Color Matrix of just the Red channel
• R, G, B refer to the values of first, second and third column of Image matrix respectively

A plausible workaround could be

Image = ptCloud.Color; %% Store the entire m-by-n-by-3 color matrix in Image

%% Extract the Red , Green and Blue Channels
R = double(Image(:,:,1));
G = double(Image(:,:,2));
B = double(Image(:,:,3));

%% the rest of the code is same

[Image Analyst]

Or

[R, G, B] = imsplit(Image);

Or

grayImage = rgb2gray(Image);

Answer 2

[Image Analyst]

What does this show?

whos Image

Assuming Image is an RGb image and you want grayscale, you can do

grayImage = rgb2gray(Image);

I'd recommend agains using Image as the name of your image since image is the name of a built-in function.

From the pseudocolored image on the right, it looks like you're using imagesc() which applies a colormap by default that is usually not wanted or helpful. I never use that. I use imshow(). So just use imshow() with no colormap.

imshow(grayImage);

If you need more help, attach ptCloud in a .mat file:

save('answers.mat', 'ptCloud');