Image resizing and saving using imwrite

hi...i need to resize the images to 512x512 and then save the image....m using imwrite to save but it saving it as blank images...my code is as below...plz help asap..

a=imread('1.jpg');
b=double(a)+1;           %converting uint to double
c=imresize(b, [512 512]);
imwrite(c,'1f.jpg');
figure,imshow(a,[]);
figure,imshow(c,[]);

[Jan]

@Horia: setting a flag is though to inform the admins about a question which conflicts with the terms of conditions. So please remove this flag and post a new question instead. Thanks.

[Image Analyst]

I moved it.

Answer 1

[Jan]

If you work with images in DOUBLE format, limit the values to the interval [0, 1]. Therefore prefer IM2DOUBLE instead of double(a)+1.

[kunal bhandari]

it worked....thanks a lot for ur help..

[Horia]

At least when resizing .gif images, you should transform from 'double' to 'logical' before using resize.Otherwise,'imwrite' will save a black transparent image. I feel this aspect isn't covered under Matlab's 'Help'.

[Jan]

@Horia: I do not agree. Converting to logical can work for black&white images only. For color images working in the DOUBLE format is sufficient, when you call imwrite with the correct inputs. If you have troubles, please post the corresponding code and the used type of the inputs.

[Image Analyst]

Horia's "Flag" moved here:

I had to use: Convert grayscale to binary MyBinary = (MyGray > 0.5); when trying to resize a transparent .gif image. Otherwise (with double(imread(('image.gif'))), I had a correct image with imshow, but imwrite('...','TransparentColor',1) saved a totally black transparent image.

Answer 2

[Image Analyst]

Don't convert to double. jpg images expect uint8 values.

[kunal bhandari]

which format wil support double?

[kunal bhandari]

converting to double is necessary for my further prgms...i have tried saving in other formats also but with the same result...

[Image Analyst]

If you want to save double images and will use them only in MATLAB, then I recommend saving them as a .mat file. If you want a visualization so that you can see them in other programs, like a jpg file, then use 255 * mat2gray() to scale to 0-255 before saving in a standard format like BMP, TIF, PNG, JPG, etc.