Creating gray scale image from selcted values

Hi, I am having trouble producing an gray scale image from selected values. I tried with the following code to convert my values in gray scale. But it's prodcuing a very tiny image. How can I get a regular size image?

P = [47 61 57; 68 53 39; 60 57 51];

grayimage = imshow(P, [0 255]);

I have also tried this one but having the same output

P = [47 61 57; 68 53 39; 60 57 51];

grayimage = uint8(255 * mat2gray(C));

I = imshow(grayimage);

Could you please help me in this matter? Thank you.

Answer 1

[Ameer Hamza]

Just create a random 2D matrix

img = rand(1000, 1000);
imshow(img);

[Koushik Paul]

Actually, the values will be in that range which I have provided here. So how can I use that value to create a regular size image?

[Ameer Hamza]

What is the range of values?

[Koushik Paul]

The range is between 0 to 80. Thank you.

[Ameer Hamza]

Use following code to generate values in range [0, 80]

img = randi([0 80], 500, 500, 'uint8');
imshow(img)

[Koushik Paul]

Thank you for your reply. I think I did not explain my problem properly. In my case, the number of values are fixed which is a 3x3 matrix. Therefore, the image which is generating is very small. But I need to produce that small image as a bigger one so that it is presentable. Thank you.

[Ameer Hamza]

Ok, I got it now. Try

P = [47 61 57; 68 53 39; 60 57 51];
img = imresize(P,[400,400],'nearest');
imshow(uint8(img));

[Koushik Paul]

Thank you so much. It worked. I have an additional question. What should I do if I want to reverse the color? Right now it shows the darkest color for the minimum value. What should I do to show the darkest color for the maximum value?

[Ameer Hamza]

There are several way to do this. You just need to subtract the values of matrix from an appropriate number. For example, reverse the entire colorspace

P = 255-[47 61 57; 68 53 39; 60 57 51];
img = imresize(P,[400,400],'nearest');
imshow(uint8(img));

It will make all the values to have a light color, however, the maximum value will have darkest color among them.

Similarly, you can also try

P = [47 61 57; 68 53 39; 60 57 51];
P = max(max(P)) - P;
img = imresize(P,[400,400],'nearest');
imshow(uint8(img));

All the elements are still dark, and maximum value is darkest.

[Koushik Paul]

Thank you so much for your help! Now the code is workng as I wanted it to.