Photoshop's Photomerge: Pt. 2

In my previous post, I demonstrated using Photomerge to create a panorama. Nowadays, if I want a panorama, I'll probably just use my iPhone, but I still use Photomerge to piece together parts of an illustration that I scanned in sections. I used to accomplish this the old-fashioned way: Using the Difference Layer Blending Mode and painstakingly rotating and tapping the image over pixel-by-pixel, but now I let Photoshop's Photomerge do all the work.

Click here to see my previous post, Photomerge Pt. 1.

There are a few things I do to prepare to use Photomerge in this way. First, I am careful that my illustration's edges are at right angles. To do this, when I trim the edges of my illustration, I use a transparent gridded rectangle against a cutting board with a grid on it. Then, in my scanner, I make sure to push an edge flush against the frame of the scanner glass. Although Photoshop can rotate the image a few degrees in Auto Blend, you'll get better image quality by avoiding this (Photoshop uses "interpolation" on images that aren't rotated at 90 degree increments, which will cause slight image degradation).

It's also important to give your image a couple inches of overlap. This gives Photoshop a margin to use in computing how to align the sections and gives room to create the Layer Mask.

I make sure that my paper edges are square and I include a
generous overlap. Click any image to enlarge.

Now, File > Automate > Photomerge. I use the default settings: Layout > Auto and I make sure the box is checked for Blend Images Together.

These are the default settings, and I use them to piece
together scans.

This screen shot shows the Layer Masks. 

I turned off one of the Layers to show the effect of the Layer Mask that
Photoshop generated.

I always check to make sure that Photomerge blended the section seamlessly. To do that, I hit cmd-1 (View > Actual Pixels) and then scroll around the seam. Once I'm satisfied with the merged sections, I'll flatten the image and start correcting the scan for color and tone, and that will be the topic of my next Photoshop Tips blog post.