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Stitching a Two-Part Scan
Software Used: Photoshop 5.5 (Any version with layers will work)

This tutorial was prompted by a forum member who needed to stitch together multiple images that were scanned from one piece because the original art work was to large to fit on the scanner bed. I've created this tutorial to demonstrate how a multi-part scan can be pieced together quite easily using layers in Photoshop. (Continued below...)

1.) The first step, of course, is to scan all the parts of your image. When scanning, the most important thing you can do is take care in keeping the image as straight as possible and try to get as much overlap between the parts as you can. My example is shown below.

The two halves of my scanned image.

2.) Next, each of the images will need to be rotated so they are facing the same direction. For my examples, the first image was rotated 90 degrees clockwise, and the second image was rotated 90 degrees counter-clockwise. You can rotate the images by selecting the image and going to Image > Rotate Canvas, then choosing any of the rotate commands from the submenu. the top half after rotating
the bottomhalf after rotating

3.) If you do not have your rulers showing, turn them on by going to View > Show Rulers. We can use the rulers to calculate the dimensions we'll need for the new image. In my example, each of the parts are approximately 400 pixels wide and 300 pixels tall. Since we have at least 100 pixels of overlap, we can assume we need to make our new image 400 pixels wide and 500 pixels tall. It's better to make the new image larger than you need, because it will be cropped later.

4.) Go to File > New and type in the width and height for your new image. For the resolution, be sure to use the same resolution that you used when the image was scanned.

Entering the dimensions for a new image

5.) Select the Move tool move tool, then drag and drop each of your scanned images into the new image. Here's my result after dragging the scanned parts into the new image:

After dragging each of the parts into a new image.

The layers palette displays each of the parts on its own layer6.) If your layers palette is not showing, activate it by going to View > Show Layers. In the layers palette, you can see that each part of our scan is on its own layer. You can select a layer by clicking on it in the layers palette. When a layer is selected you can use the move tool to move it around within the canvas.

To make things easier, I'm going to rename my layers. To rename a layer, double click on it in the layers palette, then type a new name in the resulting dialog box.

Renaming a layer.

The stacking order can be changed by draggin layers up and down in layers palette7.) I've renamed the top section "top" and the bottom section "bottom".

8.) You can change the stacking order of the layers by dragging them up or down in the layers palette. I've moved my top layer to the top of the stacking order.

9.) Use the Move tool move tool to move the layers into place so that the seam between the two parts is aligned. When the move tool is active, you can use the arrow keys on the keyboard to nudge a layer in one pixel increments. Nudge the layers around until the alignments is as accurate as possible. It may be necessary to change the stacking order of the layers to get the best results. My example is shown here:

After positioning the layers with the move tool... some seams are still visible.

10.) You can see in my example that there are still some slight seams showing due to color variations from the scanner. I've indicated the most obvious seam with a red arrow in the image above. Depending on your scanner, your seams may be more or less obvious than this. I'm going to use the eraser tool to conceal the seam.

Eraser tool options11.) Select the Eraser tool eraser tool, then choose a fairly large, soft brush from the brushes palette, and set the eraser opacity to 50%. You can access the eraser options by double clicking on the eraser tool icon. My options are shown to the right.

12.) With the top layer selected, drag your eraser brush along the seam using a series of small strokes to erase away the seam and reveal the underlying layer. By hiding the underlying layer, you can see the results of your work with the eraser. You can hide and unhide layers by clicking the eyeball next to the layer in the layers palette.

Erasing away part of the top image to conceal the seam.

13.) After using the eraser tool to conceal the remaining seams, we're ready to crop the image. Select the Rectangle selection tool rectangle selection tool and drag a selection inside your image. You can hold the spacebar down to reposition the selection as you are drawing it. (If you prefer you can use the crop tool instead of the selection tool.)

creating a selection marquee

14.) When you're happy with the selection, go to Image > Crop. Lastly, go to Layer > Flatten Image and then save the image to the format of your choice. The final cropped image from my example is shown here:

The final cropped image

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