Overlaying misregistered or offset images

[oz1]

I'm a total beginner at this so please bear with me. Also, this is my first post so "hello, all"

I have two images taken at different exposures to acquire details in a scene with very bright & dark areas.

I would like to combine them to produce a single image. I think I understand the process of using layer masks etc in PS. However, both images were acquired hand-held so they don't exactly overlay. I'll therefore need to crop both to end up with a common area with the same no of lines & pixels (x & y).

Is there any way of doing the overlaying & cropping automatically to produce two images of the same size that overlay either PS CS2 or another piece of software?

If these were satellite images, I would find a set of common ground control points to identify the image offset & then resample and or subset the two images but this is a pretty labour intensive procedure. I have done this in the past automatically using cross correlation techniques to find the image offsets but had to write the program myself.

I be very grateful for any help readers can offer.

[Daviskw]

Hi Oz

I'm sure someone here will have a much better option for you. But you can try this;

Have your two pictures on layers in the file. Change the top pictures blend mode to Difference.

Now select the move tool and get the alignment close then use the arrow keys to fine tune. When your top layer turns completely black I will be aligned with the picture below. Now just change the blendmode back to normal. There are several different procedures to blend the pictures together. If you need help there I'm sure someone can help.

Butch

[mistermonday]

Oz1, welcome to Retouch Pro!
Butch's method is probably the best when the images are copies of each other or have been taken at the same exposure settings. If no two areas of the same image are identical, alignment may be difficult. What I would try would be to reduce the opacity of the top layer to about 50-60% and get as close alignment as you can visually. Then change the top layer opacity back to 100% and nudge the layer using the Up / Down / Left /Right arrow keys. The position of most accurate alignment should appear obvious to you.
Regards, Murray

[NancyJ]

Even in different exposures you should be able to align them using a difference blend - it wont go black but you should be able to line it up correctly based on outlines

[oz1]

Thanks to all for replying.

I tried out the suggested method. The edges do show up nicely & I was able to overlay the images nicely. Now all I have to do is take good pictures!

[oz1]

There does seem to be a way of merging misaligned images automatically. Photoshop CS2 has a tick box "attempt to automatically align source images" in the "Merge to HDR" function.

See http://www.luminous-landscape.com/tutorials/hdr.shtml

I don't know how well it works but perhaps someone who has PS CS2 could advise.