Digital Outback Photo
- Photography using Digital SLRs


Photoshop Corner #018

"Stitching in Photoshop"

by Dr. William Wolberg


Why I developed this Action
In the field, I usually  carry only my 70-180 mm f4.5-5.6 micro lens that allows me to take micros of flowers, bugs etc. and moderate tele pictures.  Wider-angle shots are not possible.  However, to solve this problem, I take two vertical pictures with about a 10% overlap and then use the described technique to stitch the images.  Additionally, the resolution is greatly improved by doubling the pixel content. Essentially my 70 mm is converted to a 35 mm lens and  the 2:3 35 mm camera format is converted to a 4:5 format.
What the Action does
I don't use any of the available panorama editors because they create a blur at the seam. Rather, I use Photoshop and proceed as follows. Make a new, blank file at the same resolution as the two pictures to be stitched, but make it  wider e.g. 4000 x5000 pixels at 300 pixels/inch in the case of the Nikon D100. Then, make 50% opaque layers of both pictures and move them to the new background file.  Precisely align the two and then use the rectangular marquee tool to draw down along the middle of the overlap.  From this point on, the provided Action takes over, saves the selection and makes a new layer from the selected area, loads and inverses the selection, makes another new layer from that selection, and flattens the image.  The operator then manually crops the final image to remove excess background.
Using the Action with other lenses
With wider angle lenses, some seam editing is necessary particularly with near-far shots. Never the less, even landscapes at taken with a 24mm lens tune out very well.   One of the reasons that this method works so well for me is that I use the method mainly with my 70-180mm lens.  That lens has its own mount and the optical axis does not change when the camera is panned while in the vertical  position.  Optical axis considerations come into play in situations where the lens' optical axis shifts when panning.
Instructions for using the Stitching Action
  • Load the action into your folder Photoshop/Presets/Photoshop Actions.
  • Before you start the action, make a new, blank file at the same resolution as the 2 pictures to be stitched.  Make it somewhat larger e.g. 4000 x5000 pixels at 300DPI.
  • Then, make Layers>Duplicate and label them RBackground copy for the right and LBackground copy for the left image. 
  • Make each layer 50% opaque and move each of them to the newly created background file. Move the layers into precise alignment. 
  • Then use the rectangular marquee tool to draw down along the middle of the overlap. 
  • Change the opacity of each of the Background copy layers back to 100%. 
  • Make the right layer active and start the action.
Action for download (ZIP)

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