image editing/correcting for different scan resolutions

from HTYP, the free directory anyone can edit if they can prove to me that they're not a spambot
Jump to: navigation, search

Let's say you have two images that need to be "the same size" (or, more importantly, objects within the images – such as text – need to have a consistent size from one image to the other), but they've been scanned at different resolutions. You want to correct one of the images so that the two will be on the same scale when you put them together (e.g. if you are making two images adjacent).

Assuming the two images have not been re-scaled already, i.e. you are working more or less directly from the original scanned image, there is an easy way to do this.

  1. For each image, find the scanning resolution: select Image → Image Information... (or type SHIFT-I). Look in the "Image" box, after "pixels per inch" (or possibly "pixels per cm", depending on your settings). Write this number down for both images. We'll call this the "DPI" (dots per inch) for each image, and we'll call the image with the smaller DPI "image S", and the other one "image L".
  2. Re-scale the "smaller" image": For image S, do the following:
    • Image → Resize...
    • Take image S's "Original Dimensions" width, divide by image S's DPI, and multiply by image L's DPI. Put that number in image S's "New Dimensions" width.
    • Do the same for image S's height (note: if the aspect ratio is "locked", PaintShop will do the calculation for you automatically).
    • Press the [ Ok ] button to make the change.
  3. Both images should now be on the same scale.