convert image from uint8 to double

Hi,

Could someone tells me the difference between 'I=im2double(I);' and 'I=double(I);'. I have a simple image called 'I' with the following properties

Name Size Bytes Class Attributes

 I         512x512              262144  uint8

when I apply the first command it gives me the following error message:

??? Undefined function or method 'im2double' for input arguments of type 'uint8'.

But the second command is ok. Why?

I appreciate your help

S:)

Answer 1

[Steve Eddins]

You are getting the message "Undefined function or method 'im2double' ..." because that function is part of the Image Processing Toolbox, not MATLAB. Either you don't have the Image Processing Toolbox, or it is not installed correctly.

The function im2double scales the output double-precision values to the range [0.0, 1.0]. The function uint8 does not do this scaling.

[Sean de Wolski]

Personally, I avoid im2double for this very reason. ;)

Answer 2

[chelfremi]

I used

 pic = imread('wk2.gif');
 im2double(pic);

My original pic was Unit8

Then it gives me:

[Stephen23]

@chelfremi: As the first answer explains, that is exactly what im2double should do.

[Harizi Amira]

Where can I put this instruction to get the result in all cells ?

[Walter Roberson]

ffdouble = cellfun(@im2double, ff, 'uniform', 0);