uint8函数有什么作用？

Question

I'm trying to show the negative of an image and as you know it has a very simple code.
This is the original image:

When I use the code:

Out = 255-img;
%Out = uint8(OutNeg);
imshow(Out);  

The result will be:

But using the code:

OutNeg = 255-img;
Out = uint8(OutNeg);
imshow(Out);  

Will make the right answer:

Now I am wondering

1 - what does the function uint8() does in fact?
2 - Do these codes make the same results? In fact what is the usage of uint8?

Code1:

img2 = uint8(img1);  
imshow(img2); 

Code2:

imshow(img1,[0 255]);  

3 - Do I need to normalize the image before showing it with the following code?

img2 = 255/(max(max(img1))-min(min(img1)))*(img1-min(min(img1)));  

Or using uint8 or [0 255] does the same thing and no need to normalize??

4- what is the difference between normalizing, using uint8 and using [0 255]??????

please consider transformations like Log and power-low in your answers.

Answer 1

From help imshow :

If your grayscale image is , the default display range is
[0 1]. If your image's data range is much larger or smaller than the default
display range, you may need to experiment with setting the display range to
see features in the image that would not be visible using the default
display range. For all grayscale images having , the default
display range is [intmin(class(I)) intmax(class(I))].

By making your data an 8-bit unsigned integer ( uint8 ) array, the data is expected by imshow to be on [0 255] . RTM.