Assembling Panoramic Photos: A Designer's Notebook

2.4. Stage 4

2.4.1. Superimposing two pictures

To superimpose the two pictures in Photoshop, I used the layer masks linked to the layers. The upper image (the one I just placed) covers the background only where the layer mask is white. My task: create a layer mask on the upper layer (called "Under-exposed") and paint it black wherever I didn't want any under-exposure—everywhere except the center of the table.

This is too delicate an operation for the Brush tool, so I used the under-exposed image as a mask.

To create a layer mask on the upper layer, I clicked the "Add a mask" icon at the bottom of the Layers palette.

I brought up only this mask—totally white at this point —by unclicking the eyes next to the Red, Green, and Blue channels in the Channels palette. The channel for the mask itself must be left selected. (A quick way to do this: simply click the mask in the Layers palette while pressing the Alt key.)

The mask, which is white by default and thus transparent, appeared onscreen. I pasted the image onto it (Ctrl-V), creating a single grayscale layer.

At this stage I could see the over-exposed areas in white, and all the others in levels of gray. This was perfect, because the outlines of the mask matched the outlines of my photographs exactly. I had managed to paint my mask with just two mouse clicks!

To finish this mask, I boosted its contrast and removed the gray from the darkest areas. Using Image→Adjustments→Curves, I moved the black threshold to the right and the white ...