Why does imshow() function in Matlab return a blank image?

I am trying to perform the inverse stationary wavelet transform on an image, but I can't view the output of the image using the imshow() or image(), they both return a blank figure. I have also tried imshow(Y,[]) this also returns a blank image.

This is what I am trying to do

[A,H,D,V] = swt2(i,3,'sym4'); %input i is an grayscale/intensity image%

Y = iswt2(A,H,D,V, 'sym4') ;

imshow(Y) % the figure is white/blank %

How can I resolve this issue?

[Adam]

Have you used the debugger to actually look at Y and see if there is anything in it? The most obvious reason why imshow and image return a blank image is because you are giving them blank data to plot.

Also double-check data types.

Answer 1

[Kushagr Gupta]

Another common mistake that can yield to white or black images is a mismatch in datatypes while casting from one to another.

For example:

>> I1 = im2double(imread('coins.png')); % reads an image and converts to double in range 0-1
>> imshow(uint8(I1)) % yields a black image

This happened as the image within range [0 1] was cast into uint8 whose range is [0 255]

A better way to cast, if it is required at all would be:

>> imshow(uint8(I1*255));

But in general it is a good practice to deal with images converted to double datatype using ' im2double ' and doing further processing on these matrices.