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Combining two image files in Photoshop

When turning two sided images such as postcards or small format letters into a single image for ease of posting online. This assumes that the two sides will have one matching dimension (i.e. 720 or 750 pixels as our approved longest dimension for posting online). See end for notes on how to change this process for items without any matching dimensions.

Open both jpg files in Photoshop. Decide if they’ll go side by side or top to bottom. You need to figure out the end dimensions of the overall image. Instructions for both are below but only top-bottom is pictured.

Pull up the second image file. For side by side, that will be the one that will be on the right, for top-bottom that will be the one that is on the bottom. You can get the dimensions of the image in 2 ways.

One is to select the image with the rectangular marquee tool, you’ll see as you’re holding the left click button down on the mouse, there will be a little pop-up with the dimensions in pixels for both width and height. For top-bottom orientation, note height. For side by side orientation, note width.

Looking at the image size via the rectangular marquee tool

Alternatively, click on Image on the tool bar, select either Image size or Canvas size and note the appropriate measurement there. You’ll want to work in pixels instead of inches (it may default to inches as the displayed measurement) for accuracy.

How to find the pixel count from the Image menu

Once you have the measurement noted, select the whole image and copy it. <ctrl>C is simplest.

Close out this image file. Look at the other image file. Go to Image on the toolbar, select Canvas size.

How to find Canvas size from the toolbar

Look at the relevant dimension: height for top-bottom, width for side by side.

Looking at the canvas size

Add the two heights or widths of the two image files together. In this example, we’d add the 473 pixels of the back image to the 467 pixels of the front image. Type that in the appropriate box (height for top/bottom, width for side by side). You’re increasing the overall canvas size of this image to make room to copy in the other image.

Next up, you’ll want to orient this image to the correct half of the increased size canvas, since it defaults to centering the image. To correct this, you need to click the appropriate arrow in the Anchor section of this pop-up. For top/bottom, click on the up arrow. For side by side, click on the left arrow. The Anchor graphic will move to show the change. Click okay.

You’ll now have an image that looks like the following.

Image placed on one half of the canvas

Use the rectangular marquee tool to select the bottom half of the image (the blank white area) and paste the other image in using <ctrl>v. You’ll end up with the two images pasted together.

Images pasted together

There’s one more step before you save the new jpg. Since Photoshop treats this copy/paste as multiple layers, it won’t allow you to save the current file as a jpg, since jpgs don’t allow for layers. Click on the Layer menu on the toolbar, head to the bottom–it’s nearly at the end of the list, and click on Flatten Image. Once that is complete, you can save the new image file as a jpg.

Finding Flatten Image from the toolbar.

If your images do not have matching dimensions in the direction you want to join them, such as a postcard that’s oriented portrait on the front and landscape on the back or similar, choose the larger of the two images as your base canvas file, and enlarge it to account for the additional width or height and using the Anchor function, move it to whichever size of the canvas is appropriate, and then you can paste in your second image. Remember that the canvas size is now larger than the final dimensions of what you are pasting in so you may want to select only a portion of the blank canvas to paste into—depending on if you want to center the second image, top, right, bottom, or left justify it.

And you’re done!

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