How to Implement an “imshow” function?

How to Implement an “imshow” function by transforming the range [min, max] on the gray scale into the interval determined by 0 ≤ a, b ≤ 1? I need use variables and it should be suitable for any image not particular. Thank you!

Answer 1

[Anna Nazarova]

The result should be like this. And if I use your code than the image not changing

[Rik]

Because you posted your comment as answer it is not clear who you are responding to.

If you are responding to Walter: What exact code did you use? Because the mat2gray function should do this for you.

If you are responding to me: What values did you set a and b to? Please post the code you used.

[Anna Nazarova]

Rik, this code:

IM=imread('girl.jpg');%generate 'image'

a=0;b=255;%define upper and lower bound

IMsc=double(IM);%make sure it is a double

IMsc=(IMsc-a)/(b-a);

IMsc(IMsc<0)=0;IMsc(IMsc>1)=1;

figure(1),clf(1)

subplot(1,3,1)

imshow(IM,[])

title('original')

subplot(1,3,2)

imshow(IM,[a b])

title('original (scaled)')

subplot(1,3,3)

imshow(IMsc,[])

title('scaled result')

[Rik]

Of course the image is not changing: you have defined a and b is such a way that it will not change. The data type that most images will have when loaded is uint8. This has a minimum of 0 and a maximum of 255. If you want to change how the image looks, there are multiple methods:

1. the method I showed you, where you will have to define a and b yourself, or use a=min(IM(:));b=max(IM(:));
2. the method Walter suggested: use mat2gray(IM) (note that mat2gray(IM,[a b]) is equivalent to my method. mat2gray is in the image processing toolbox, but you appear to have that anyway.)
3. the method Image Analist just suggested: don't change the data, but use the empty square brackets to display you image with a scaled color scheme by using imshow(IM,[])

Which of these you think is best for your situation is for you to decide.

[Image Analyst]

I also suggested #2. And there is yet another way that might be useful. It's imadjust(). With imadjust(), you can specify a percentage of the way to come in on the tails of the histogram to determine the range. that way, outliers (like salt and pepper noise) will not prevent a nice picture from appearing.

Answer 2

[Image Analyst]

To display a gray scale image without changing the values of the array, but only changing the displayed values, do this:

imshow(grayImage, []);

To change the actual matrix, use mat2gray():

% Scale grayImage to between 0 and 1: min goes to 0, max goes to 1
grayImage = mat2gray(grayImage);

[Anna Nazarova]

Thanks everyone, it works!

[Anna Nazarova]

So I have a problem. It works with imadjust() function, but I don't know how to use

imshow(grayImage, []);

I need to use this function. If you know, please write a code. Thank you!!

[Image Analyst]

Not sure what you're asking.

imshow(grayImage, []);

works, as does

imshow(imadjust(grayImage));

The [] are not needed if you use imadjust since the output of imadjust is already scaled from 0 to 255.

[Anna Nazarova]

Can you please send full code?

[Image Analyst]

Yes, you can find it here