605 Auto-stitching scanned artwork in Photoshop

- Hey gang, this is Deke McClelland. Welcome to Deke's Techniques. This week I'm going to show you how to stitch together multiple scans automatically inside Photoshop, and to put things in context I'm going to share with you a personal story if you'll permit me. I have a girlfriend named Colleen. She is very beautiful but that has nothing to do with this story. Her grandfather owned and operated a deli in Fort Bragg, California. This is his drawing of the deli, so he was secretly an artist, and he would create their print ads including this accomplished piece of craftsmanship right here.

Thing is it's more than 50 years old, so I wanted to digitize it and bring it into Photoshop. Now, I could have had it scanned professionally of course, but supposedly I'm a professional, so I decided to make use of our four-in-one printer here at the studio which doesn't do any of its four activities very well. It only supports by the way eight a half by 11 sheets of paper, so I had to scan the thing in two passes, and by necessity one of the passes was upside down. Now, at the center of the art, the art starts coming away from the surface of the glass, and as a result, these edges right here are a little bit blurry, and yet miraculously Photoshop is capable of treating these scans as a panorama and stitching them together automatically as we're seeing in this final piece of artwork.

And if you look very closely at the center, you will see that there are no seams. Here, let me show you exactly how it works. All right here's the final pristine version of the ad, just so you can see it on screen, and here are each of the scanned halves, which I haven't edited at all by the way, which is why this guy's upside down. The first step is to combine the two into a single document, and so armed with my Rectangular Marquee Tool, which you can get by pressing the M key, I'll right-click inside the image window and choose Duplicate Layer, and then I'll go ahead and send this guy to the first scan and click OK.

Now I'll switch to that document so that we can see both of the layers. I'll double-click on the name for this guy and change it to R for Right, and then I'll double-click on the Background to convert it to a layer, and I'll name it L for Left, and then I'll click OK. All right now the next step is to select both of the layers, very important. By clicking on one and Shift + Clicking on the other here inside the Layers panel, and then you want to go up to the Edit menu and choose Auto-Align Layers. You can leave Projection set to Auto as by default. These are scans, not photographs, so you don't need to worry about the Lens Correction checkboxes.

In fact you want them to be turned off, at which point I'll go ahead and click OK in order to automatically align those layers. Notice that Photoshop is smart enough to flip the right-hand scan. The problem is that auto-projection setting requires Photoshop not only to flip the scan but to distort the two scans as well, and that all happens in a single operation, which is pretty calculation intensive. So if you zoom in here, and then you select the right layer and tap the 5 key to reduce its opacity to 50%, you'll see that the alignment is pretty sketchy.

Turns out we can get better results if we give Photoshop a little bit of assistance. So I'll press Control + 0 or Command + 0 on the Mac to zoom out, and then I'll press Control + Alt + Z a couple of times, that's Command + Option + Z on the Mac in order to reinstate the original layers. Then with the R layer selected, I'll just go up to the Edit menu, choose Transform and then choose Rotate 180 degrees, and that will go ahead and rotate that layer so it's upright. Now Shift + Click on the L layer, so that both of them are selected there inside the Layers panel.

Return to the Edit menu and choose Auto-Align Layers. We don't need to do anything inside the dialog box, just click OK, and then a moment later you'll see the two layers aligned with each other. All right I'm going to go ahead and zoom in again. This time I might as well Control + Spacebar + Drag, that's a Command + Spacebar + Drag on the Mac. Then I'll click on that right layer to select it, and I'll tap the 5 key in order to reduce the opacity to 50%, and notice this time we've got a dead on match, so things are looking much, much better.

All right now I'll press Control + 0 or Command + 0 on the Mac to zoom out. I'll tap the 0 key to reinstate an opacity value of 100%. I'll Shift + Click on the L layer once again so that they're both selected, and now you want to return to the Edit menu and choose Auto-Blend Layers this time around. Now it's tempting to select Stack Images because after all the two images are stacked on top of each other but that's designed to accommodate a single scene that you shoot multiple times, and then overlay to get rid of things like noise and people in the shot, and stuff like that.

In our case, because the two scans are side by side, they amount to a panorama, so go ahead and select Panorama. You do want Seamless Tones and Colors to be turned on. There's no sense in turning on Content Aware Fill, it'll just waste time. At which point I will click OK in order to get the ball rolling and we can see a moment later that we have what ultimately amounts to a seamless composition, but we do need to test that just to make sure that we really don't have any seams. So I'm going to zoom in once again and now I'll Control or Command + Click on the layer mask thumbnail for that right layer so that we can see the seam, and notice the top of the frame looks great, and it's totally uncanny how Photoshop is able to divide the words apart from each other with the exception of gourmet.

You can see that it goes down the center of the M, but if you're concerned about that, you can press Control + H or Command + H on the Mac to see if you see a seam, which I don't, I think it looks great, and so I'll press Control + H or Command + H on the Mac to bring back that selection outline. Look at how the selection goes between the words of and, what is that word, nostalgia, so that looks great. We do have some problem in the Gouda however. Notice that we've got a bad edge right there, and so we'll take care of that in just a moment. But continuing down everything looks great all the way to the bottom of the frame, so I'm just going to press Control + D or Command + D on the Mac in order to deselect the image, and now let's take care of that piece of cheese by first turning off the mask for the left layer.

Because notice, if I turn off the right layer, we have the mask right there which is not doing us any good, so I'll just go ahead and Shift + Click on it here inside the Layers panel to turn it off. You don't have to delete it, because you might want to come back to it one day. Then go ahead and turn the right layer back on like so, and I want you to see something about these layer masks. If I Alt or Option + Click on this layer mask thumbnail so we can see it independently of the rest of the image, notice it's very jagged. So every pixel is either black or white, nothing in between.

Which means that if we're going to modify this mask, we need to keep it jagged as well, so I'm going to go ahead and Alt + Click on this layer mask thumbnail. You want it to be selected here inside the Layers panel, and then go ahead and click and hold on the Brush Tool and select the Pencil Tool from the fly-out menu, because after all the Pencil tool always produces jagged brush, because after all the Pencil tool always produced jagged brush strokes. All right now I'll increase the size of my brush cursor to, let's say about six pixels should do, and then you want to tap the D key in order to instate the default foreground and background colors.

Followed by the X key so that the foreground color is black. And now, just go ahead and paint over this line like so, and you want to be very careful that you don't paint into the neighboring line, but I do want to bring back the natural antialiasing that's associated with this scan, and so I'm going to paint that edge in until it looks nice and smooth, as we're seeing right here, and that is it, that's all we need to do, where stitching the scans together is concerned.

Now obviously we need to apply some clean up, and so the first step is to click on the layer thumbnail here inside the Layers panel, and then I'll go up to the Window menu and choose the Channels command to switch to the Channels panel, like so, and notice the Blue channel is very dark. The Green channel is a little bit brighter, and the Red channel is the brightest still, and most closely resembles the final effect we're looking for. That is to say we have the most contrast between black and white which is all we want in the end, and so I'll just go ahead and switch back to the RGB image, switch back to the Layers panel as well.

I'm going to select both of these layers here, and I'm going to group them together by going to the Layers panel fly-out menu and choosing New Group from Layers and I'll go ahead and call this group stitched, let's say, and that'll just protect them from further harm. Now I'll go up to the Layer menu, choose New Adjustment Layer, and choose Channel Mixer, and I'll call this layer red only, and click OK. All right now I ultimately want a monochrome image. That is, black and white, so I'll turn on the Monochrome checkbox, and we're looking for red all by itself, so I'll change the Red value to 100%, and I'll take both the Green and Blue values down to 0%, and that's all there is to that.

All right now we need to increase the contrast by returning to the Layer menu, choosing New Adjustment Layer, and this time around, choosing the Levels command. I'll go ahead and call this new layer contrast, and then I'll click in this black point value and I'll press Shift + Up Arrow a bunch of times in order to increase that value to 70 so that anything with a luminous level of 70 or darker is becoming black. That is going to clip some colors, but that's exactly what I want. I want some nice, rich blacks inside of the final ad.

Now I also need to clip some whites so I'll go ahead and double-click on the thumbnail for this layer to bring back the Properties panel and I'll reduce that white point value to 200 so that we have this pristine effect right here. Or at least, it's mostly pristine. Notice that we do have a little bit of garbage, and that stuff that I'm just going to have to hand paint away using the Brush Tool by the way, and to make that happen, you would select the Brush Tool, you'd create a new layer by the way to accommodate your brush strokes. Then you would right-click inside the image window and crank the Hardness value all the way up to 100%, and then you would very carefully paint, which is a little boring to watch.

So thankfully I've done it in advance, and so I'll just go ahead and switch over to that image, and notice this whiteout layer right here. That is my layer of paint, and so to bring it into my image in progress, I'll go ahead and switch to the Rectangular Marquee Tool, I'll right-click inside the image window, choose Duplicate Layer, and then go ahead and select that first scan once again, and click OK, and now if I switch back to that image, you can see that all is well. So here's the image without that layer, and here's the image with, and now everything is exactly the way I want it.

At which point I'll press Shift + F to switch to the full screen mode, and I'll press Control + 0 or Command + 0 on the Mac to center my zoom. And that, friends, is how you stitch multiple scans together, whether it's two, or three, or four scans, using a combination of two commands known as Auto-Align Layers and Auto-Blend Layers here inside Photoshop. If you're a member of lynda.com, I have a followup movie in which I show you how to automatically trim the artwork without clipping it at all, so this is all nondestructive, so that every boundary is exactly the same size.

If you're waiting for next week, I'm going to show you how to infuse the artwork with a crinkly paper texture using the Clouds filter. Deke's Techniques each and every week. Keep watching.