Quickly Spot Mistakes in Your Photoshop Masks

If you do any kind of Photoshop work using selections and cutouts, you’ll know how important it is to be as accurate as possible, particularly when working with images of people. It’s easy to miss areas of an object when using the Quick Selection tool, especially when working in intricate areas such as hands, bits of clothing and so on; irregularities can stick out like a sore thumb – or a missing one. They also have a habit of only showing themselves after we think we’ve finished the cutout, or worse still, we don’t notice them at all!

Here’s a little trick and technique for quickly highlighting areas that we’ve missed using the Difference blend mode. Difference works by comparing the currently active layer with the layer beneath. Any pixels in the two layers that match perfectly are turned black, any non-matching areas show up in their normal state, making it immediately obvious where we’ve missed areas in the original selection. The technique relies on using a layer mask to make the extraction, as we need to be able to restore the missed areas. This is good practice for any cutout, of course.

Let’s see it in action.

 

We’ll start off by making a selection of the woman using the Quick Selection tool (keyboard shortcut: W). I’ve deliberately left portions of the selection out to demonstrate the technique more clearly; in real-world situations the omissions would probably be more subtle.

 

Open up the Refine Edge dialog by clicking the button in the Options Bar or by going to the Select menu and choosing it from there.I’ve set the view mode to On White (shortcut W) as it will highlight areas of the original grey background, allowing us to adjust the edges and remove any haloing. As the background has been hidden, it’s difficult to spot where we’ve missed parts of the hat and the woman’s waist; even in this exaggerated version. I’ve made some minor adjustments and, most importantly, I’ve set the output to New Layer with Layer Mask. Click OK to apply the changes.

 

Here’s our cutout. Photoshop hides the original background layer once Refine Edge is applied with the layer mask output selected, so it’s isolated and set against the checkerboard pattern. Again, it would be difficult to see minor omissions in the selection at this point.

 

We’ll turn the original layer back on using its eyeball icon in the Layers panel. Now we’ll change the extracted layer’s blend mode to Difference. Any pixels in the top layer that match the original turn black, so we can instantly see the parts we’ve missed. We can also see the vague outline around the figure where we adjusted the edge.

 

All we need to do now is adjust the mask to reveal the missing areas. Grab the Brush tool (shortcut B). We’ll make sure the cutout layer’s mask is selected by clicking its thumbnail in the Layers panel. Now we can start to paint over the missing areas in white using a small, fairly hard brush tip for greater accuracy. As we do, the pixels start to turn black. Remember, we’re not painting over the image here, we’re merely revealing the masked area so it now matches the original and those pixels are blocked out.

 

We’ll continue painting over the omitted sections until the figure is complete. We can now hide the original layer again. Remember we’re still in Difference mode; the cutout now shows up correctly as it has nothing to blend with. Change the mode back to Normal. We’re ready to place our woman into a new scene.

 

I hope this short tip and technique is of use to you. Until the next time, take care!

David