When we take multiple images into an HDR program, during the registration (alignment) process the program will twist and turn each image to align it with the image below, using either common features or horizontal/vertical lines. When it does so, at the end (if enabled) the program will then crop the image so that there are no ragged edges.
The problem is that those crops may not be a standard size or aspect ratio. Part gets cut off, this may just be a few pixels if the camera was on a steady tripod but can easily equal an inch or two if you attempted a handheld 3 shot image ( I have successfully). 
So what needs to be done after you finish the entire HDR process and have your final Tiff/JPEG image is to now take the image into a photo editing software of choice ( you can crop in Photomatix, but I prefer other editors) and crop the image to a standard size.
This standard size can be one of two things: a standard image size that comes out of a camera or a 2:3 aspect ratio image ( or 3:4 for some point and shoots) Or you could crop to standard Frame/Matt sizes that can be very different.
Standard camera sizes in inches would be 6 x 9, 8 x12, 12 x 18, 16 x 24, 20 x 30 etc.
Standard Frame sizes are: 8 x 10, 11 14, 13 x 19, 16 x 20 etc.
Your choice your descion. I always crop to standard Camera sizes and then will do special crops if I decide to have a image a certain frame size. Be aware that you can get some frame sizes in size the same as camera sizes.
When you do crop an image, you really only want to throw away the pixels that aren’t necessary, you want to try to not change the pixels that are left behind. Either making less of them or creating more than were there in that space originally. If you do that will require Interpolation on the part of software. This interpolation can cause some ( mostly not visible) softness or color shift in our images. We want to minimize that.
So when we do crop try to do so that no pixels inside the crop area are harmed. To do that in Photoshop, set a crop size in the tool bar, Say 12 x 18 and then leave the resolution box blank. This will crop the image to the document size of 12 x 18 but will not alert the pixel within in any way.
All this will tidy up your images and make for an easier time when it comes to print your images, and I DO want you to print your images. Either at home or by a High Quality Lab. You will love the results and the sense of finish that a print brings.
Hope that helps!
PT
One Comment
Very timely article! Thank you, I’ve been wondering about this! I crop to standard frame and mat sizes so I don’t have to pay for custom, it’s mostly worked for the pictures I’ve printed.