Why imwrite doesn't work??

I have a .mat file of Lena(greyscale) and i want to use imwrite to trnsfer it to a jpeg file. so i used:

load Lena;
imwrite (Lena, 'lena.jpg')

there is a jpeg file being generated but it is all white (all values are 255). I don't know why is that?

[Stephen23]

@Chen Ji: please show us the outputs of these commands:

class(Lena)
max(Lena(:))

[Chen Ji]

Oh! I worked out caz i found that the input matrix for imwrite should in [0,1] and my Lena element range is in [0,255]. Then i divide each element by 255 and then it worked. It should be a correct solution, right? Thx!!!

[Stephen23]

"found that the input matrix for imwrite should in [0,1] "

This is not correct: the input range actually depends on the image data class. If you have an image of class double then dividing by 255 may work, see my answer for another solution.

[Chen Ji]

I used the code in your answer and the commend is "double" and 240

Answer 1

[Stephen23]

Your image has double values on range [0,255], so you need to scale the values to [0,1] or change the class:

imwrite(uint8(Lena), 'lena.jpg')
imwrite(Lena/255, 'lena.jpg')