How to create a gray scale image

Hi, i want to create a gray scale image in matlab so I write a matrix 5x7 lets say A=[0 0 0 0 0 0 0; 80 80 80 80 80 80 80;200 200 200 200 200 200 200; 110 110 110 110 110 110 110; 160 160 160 160 160 160 160;255 255 255 255 255 255 255] . Then i use the imshow command and I expect an image where every row has a different intensity, the first black, the last white and the others with intermediate values. Instead of that i get a picture where only the first row is black and the rest of them are white. what am i doing wrong?

Answer 1

[Image Analyst]

A is a double. Cast it to uint8:

imshow(uint8(A));

or else use [] if you want to keep A as a double:

imshow(A, []);

[maria]

thanks a lot, it worked :) but what is actually difference between double and uint8 ?

[Image Analyst]

A double is a 8 byte (64 bit number) that can represent a wide range of numbers, including those of fractional values. A uint8 is a 1 byte (8 bit) number that represents only integers in the range of 0 to 255.

[maria]

great, but even in that case matrix A has only integers. should't it be able to give me a grayscale image even though it's double?

[Image Analyst]

It is a grayscale image - a floating point grayscale image. But it's not an integer class . It's a double class that happens to have only integers in it, but it's still a double. Look:

A=[0 0 0 0 0 0 0; 80 80 80 80 80 80 80;200 200 200 200 200 200 200; 110 110 110 110 110 110 110; 160 160 160 160 160 160 160;255 255 255 255 255 255 255] 
whos A

 A     6x7    336  double

[maria]

but my matrix represents a filter, and i want to impose it in an image. should i convert it to uint8 or is it fine if it is double?

[Image Analyst]

It's fine if it's a double. You'll get more accuracy that way. You only need to convert it to an integer if you want to do certain things, like store it in a standard image format.

[maria]

oh ok, thank you so much for your help :)