How to enhance video frames in while cycle

Hi, I've a problem with the enhancement of video frames and I hope you can help me.

First, I have worked on a .png image taken from a .MOV video, converted it in gray scale, adjusted contrast and equalization, the following is the code:

image = 'name.png';
IMG = imread(image); % read image
I = rgb2gray(IMG);   % convert image to gray scale
I2 = wiener2(I);     % filter
I3 = imadjust(I2);   % adjust contrast
contrast = 0.01; 
I4 = adapthisteq(I3,'clipLimit',contrast,'Distribution','uniform'); % equalization
figure, hh = imshow(I4,'InitialMagnification', 'fit');

Now, I would like to do the same but directly with the video frames. Here is what I did:

xyloObj = VideoReader('name_video.MOV');

while hasFrame(xyloObj)
    % Read frame
    vidFrame = readFrame(xyloObj); 
    % Enhancement
    I = rgb2gray(uint8(vidFrame));
    I2 = wiener2(I);
    I3 = imadjust(I2);
    contrast = 0.01;
    I4 = adapthisteq(I3,'clipLimit',contrasto); 
    figure (100), imshow( uint8(I4), 'InitialMagnification', 'fit');

      pause(0.01)

end

The figure (100) shows an almost black image, despite the enhancement is the same of above (for the .png image worked quite well). I wonder why...

Thanks for the help!

Giovanni

ps. I attached 3 images to help you to understand my problem. Maybe you can suggest me also I to enhance that properly :)

Answer 1

[Geoff Hayes]

Giovanni - in your while loop, you cast I4 as 8-bit unsigned integers which you don't do with your initial example. What can you tell us about the I4 from your while loop? Try executing the following commands

 class(I4)
 min(I4(:))
 max(I4(:))

to determine the data type (class), minimum and maximum values in this matrix. It could be that they are doubles and in the interval [0,1] and so when you cast to the unsigned integers, you get zeros or ones. And if most of the values are zeros, then you would see a black image. I suspect that you may want to remove the cast...

[Giovanni Pavese]

_Hi Geoff, I'm not sure to have understood your answer. I supposed that the problem was in the input of imshow, so I put uint8 in the while loop, but I'm not so expert in video processing. However I wrote

I4 = adapthisteq(I3,'clipLimit',contrast);
class(I4)
min(I4(:))
max(I4(:))

and the result was

class = uint8
min = 4
max = 255

thanks for answering :)