Matrix multiplication within a function not working

2021 9 19
2 个回答
更新时间：2021 9 19
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0 个投票

The following function creates a column vector and an image histogram:
function lutlum = lutlummer(image)
for i = 1:1:265
lutlum(i, 1) = i-1;
end
%multiplying the LUT with the luminescence histogram of the image
%Finding luminance image 'L' (Formula gained from class slides)
L = uint8(sum(bsxfun(@times,double(image),reshape([0.299 0.587 0.114],[1 1 3])),3));
%Finding luminance histogram'HL'
HL = histcounts(L,[0:256])';
lutlum = lutlum*HL;
end
The function is called with an image such that HL is a 1x2 matrix, so multiplying a 265x1 matrix ('lutlum') with a 1x2 matrix should be no problem. however, i still get this message:
Matrix dimensions must agree.
Error in ImageProcessingLab2>lutlummer (line 469)
lutlum = lutlum.*HL;
Please do let me know where i am going wrong
thanking yall in advance!! :D

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Image Analyst
Image Analyst 2021-9-19
image is a built-in function. Do not use it as the name of an input variable.
What is the size of your image?
Bharath Nagarajan
Bharath Nagarajan 2021-9-19
Dully note, thank you for tyhe feedback! my image is 387x713x3
Image Analyst
Image Analyst 2021-9-19
What is L? Is it the gray scale version of the color image like you'd get from rgb2gray()? If so, why would you multiply the 1-D histogram bin count by a 2-D image?
Bharath Nagarajan
Bharath Nagarajan 2021-9-19
L is supposed to be the 'Luminescence image' and it appears that it is a greyscale image. Howvere, I am trying to multiply lutlum (256x1 matrix) with HL (a 1x2 matrix). this should still work though right? since the matrix dimentions are compatable?

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回答（2 个）

0 个投票

There is an err, here is how it is to be:
lutlum = HL.'*lutlum; % creates 2 - by - 256

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Bharath Nagarajan
Bharath Nagarajan 2021-9-19
Unfortunately it still throws the same error
Error using *
Incorrect dimensions for matrix multiplication. Check that the number of columns in the first matrix matches the number of rows in the second matrix. To perform elementwise multiplication, use '.*'.
Error in ImageProcessingLab2>lutlummer (line 481)
lutlum = lutlum.'*HL;
and even when the order of matrices are switched:
Error using *
Incorrect dimensions for matrix multiplication. Check that the number of columns in the first matrix matches the number of rows in the second matrix. To perform elementwise multiplication, use '.*'.
Error in ImageProcessingLab2>lutlummer (line 481)
lutlum = HL.'*lutlum;

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0 个投票

There are a couple of errs in the code. Here is the corrected version:
function lutlum = lutlummer(image)
for i = 1:1:256 % Has to be 256 NOT 265. 256 similar to 265 :)
lutlum(i, 1) = i-1;
end
%multiplying the LUT with the luminescence histogram of the image
%Finding luminance image 'L' (Formula gained from class slides)
L = uint8(sum(bsxfun(@times,double(image),reshape([0.299 0.587 0.114],[1 1 3])),3));
%Finding luminance histogram'HL'
HL = histcounts(L,[0:256])'; % Note the size of HL is 256 - by - 1 NOT [1 - by - 2] as you have stated
lutlum = lutlum*HL'; % Transpose is necessary
end

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