On Tuesday 21 July 2009 01:58:33 pm James Cobban wrote:

I am trying to combine images scanned from microfilm in the case where the lens on the microfilm scanner is too powerful to permit me to scan an entire page into a single image file. I believe that this application is similar to trying to create a landscape from multiple photographs.

I scan the original into a PDF containing multiple images. I then open this PDF as layers. I have been able to rearrange the layers, raise and lower them, and merge them to create a single image file, but I have 2 problems:

1) Sometime the key spots within the layers which I need to line up prior to merging the layers are not right on the edge of either layer. To perform the alignment I need to make at least the outer portion of the upper layer partially transparent so I can properly align them.
2) Once I am finished the contrast between the two layers is generally such that the edge of the upper layer is clearly visible in the merged result. Once again if I could make the outer edge of the upper layer transparent on a gradient to fully transparent at the edge, I could make the edge invisible. I think of this operation as "feathering" the layer, but searching through the documentation and web guides I can only find "feathering" as applicable to images, not layers.

The following is an example of the result I currently have:

http://www.jamescobban.net/Ontario/images/B1912_33007.jpg Combined image from microfilm.

This is described well in "The Artist's Guide to Gimp Effects", page 47. Basically it involves applying a gradient to a layer mask.