This operation is done if you have two images of the same area of an inscription, and want to make a common drawing that will reflect the information on both images.
1. Open the two images and choose the image that will be the "base" image to which all other images will be sized (we'll call that "Image 1"). We'll call the other image "Image 2."
2. Make sure both images are the same resolution.
a. Select menu item "Image - Image Size."
b. If both images are the same resolution, go on to step 3.
c. If the resolution of Image 2 is different than Image 1, make sure "resample image" is not checked, then type in the new resolution for Image 2 and click "OK." The overall size of the image will not actually change at this point.
3. In Image 1, select the measure tool. If the image has a measure or scale in it, click on both ends of it. A measuring line will appear between the two points. The ends of the line can be moved by clicking and dragging on the + at either end. The entire line can be moved by clicking and dragging on the line itself. Be sure to zoom in quite closely to make sure the ends of the measuring line are where you want them.
4. Check the length of the measuring line in the "Info" palette.
5. Follow the same procedure in Image 2.
6. Divide the length of the line in Image 1 by the length in Image 2. The result will be a decimal.
7. Convert the decimal to a percentage (e.g., .97 will become 97%). Select Image - Image Size. In one of the top dimensions, select "percent" and type in the number obtained above (Note: it has to be a number between 1 and 100--make sure it is not the decimal obtained in #6). Click "OK."
8. Go back and remeasure each image--they should now be extremely close to one another in scale.
9. If the image has no scale, choose an object in each of the images that is relatively easy to measure and use it to do the sizing.
There are two other aspects to an image which might make it difficult to match drawings in each of the images. One is rotation, which is easily fixed. The other is skew, which is extremely difficult and beyond the capabilities of Photoshop to address. Skew has to do with the relationship between the plane of the object and the plane of the film during photography. This relationship is rarely exactly the same between one photographic setup and the next and the problem is made worse when years or decades intervene between photographs. The problem is not too bad for two dimensional manuscripts, but can be a serious problem for three dimensional inscriptions such as monuments, seals, ostraca, etc. At this point, there is little that can be done to correct this problem using conventional imaging programs. We are working on the problem, however, and will keep you up-to-date on our progress.