Why is the lenna image rotated?

Opened lenna.raw file in figure.

By the way, the image is rotated 90 degrees counterclockwise. It was a 256x256 image, and I printed the image using mat2gray.

I'm curious as to why and how the image is spinning.

please help me thank you.

[DGM]

mat2gray() doesn't save or print anything. It just takes a weighted average of the image channels.

Without knowing what you did to the image and what you're doing now, nobody has any way of knowing. Attach a small example of the code which can demonstrate the problem.

I'm going to go out on a limb and guess that you're doing some point-by-point looping and you have your row and column subscripts swapped.

[niniki]

raw = fopen('lena.raw')

a = fread(raw,[256,256])

b = mat2gray(a)

figure(1)

imshow(b)

This is the code I wrote.

[DGM]

When you read the image into a rectangular geometry such as in this call:

a = fread(raw,[256,256])

understand that what you're doing is taking the raw data in the file (a vector) and devectorizing it. This is the same as reshaping any other vector.

Consider the example:

myimagevector = 1:25; % pretend this is the image data
myimagematrix = reshape(myimagevector,5,5)

myimagematrix = 5×5

1 6 11 16 21 2 7 12 17 22 3 8 13 18 23 4 9 14 19 24 5 10 15 20 25

The contents of the vector are placed columnwise into the output geometry. If the original data had been written out row-wise, then the result will be transposed -- not rotated.

@yanqi liu is correct. All you likely need to do is transpose the incoming image.

[niniki]

Thanks to your answer, I understood perfectly!!!! ^^b

Answer 1

[yanqi liu]

yes，sir，may be check

https://ww2.mathworks.cn/matlabcentral/answers/258485-how-to-read-a-raw-format-image-data-into-a-matrix

when read it，should use ' to transposition the matrix

fid = fopen('lena256.raw', 'rb');
x = fread(fid, [256, 256], 'uint8=>double').' ; 
fclose(fid);
figure; imshow(x, [])

[niniki]

thank you!!