Images and canvas size

[stopfordian]

A bit of a long shot but as we have very knowledgeable people in this forum, I thought I can only ask (and I've spent too many hours trawling search engines to find nothing)...
I have images which I do not want to resize or scale - I simply want to increase the canvas size without altering the image size.
As I have several thousand images, I need to do this using some sort of batch processing method.
I want to be able to input a minimum width for the canvas - if the image width is greater than my input, do nothing. And, if the image width is less than my input, increase the canvas to my minimum width. I also want the same thing for height.
I have searched for, and tried, many graphics resize programs. The best, by far, has been FastStone Photo Resizer - but this only lets me change the canvas to a set size. I also own Fireworks 8 but again, I can see no way to do what I want.
I have also tried Photoshop and Paint Shop Pro to no avail.

Does anyone know of a suitable program?

You will help stop me going insane!

[jont]

Have you seen Marks post here http://community.actinic.com/showthread.php?t=23922&highlight=fireworks

[stopfordian]

Have you seen Marks post here http://community.actinic.com/showthread.php?t=23922&highlight=fireworks

Yes, I had tried that but it gives me the same canvas size for all images (although it did solve another problem I have been having:) . I am after something slightly different:

If my image is 150x439 and I want a minimum width of 200, I need the outcome as 200x439.
If my image is 256x512, my minimum width of 200 will leave this image as 256x512.

I think I am going to have to change my approach and start using several standard canvas sizes, say 100x100, 200x200, 300x300, etc., so my 150x439 will have to go in at 500x500.

Ah well, I'll just have to alter my ways of working.

[jont]

Using windows explorer navigate to the image folder, ensure view is set to details and then click the "dimensions" column .. this will then list the images by size ... simply copy the smaller than needed images to a temp folder .. run the batch on the temp folder then copy back into the main images folder