Tuesday, April 3, 2012

Stitching Together Scans in Photoshop

A little project that I have been working on lately is scanning my smaller paintings on my desktop scanner/printer. Even my smallest pieces are too large for the 8.5" x 11" scanner bed. But with my smallest paintings I can at least get the whole image in just two passes. Which means that I have two nice 300ppi images that once I put together, I can hopefully use to make prints.


I put these scans together using Photoshop 7. The first thing I did was to open up both halves in Photoshop and make sure they were rotated correctly.




Then I go to Image > Image Size and check the size of my two images. I am mainly concerned with getting the width right for my new image. There is plenty of overlap in the scans, so the length of the new image just needs to be bigger than the two images. I will crop the new image when I have pieced it together. After I have checked the image sizes of my two scans, I go to File > New and when the dialogue box comes up, I copy and paste the width of my scans in for the width of the new image, and I guess about the length. Each scan was 8.5", so 17" for the height of the new image will work.




Next I select the move tool and drag and drop my two halves into the new image.





I line them up as best as I can with the move tool. When the move tool is active I can use the arrow keys on the keyboard to nudge the images into place pixel by pixel. Until they are merged each image is a separate layer, and I can navigate between them by clicking on the layer I want in the layers box, or by checking the auto select layer feature of the move tool and simply clicking on the layer I want to move.




Since there is a lot of overlap in the scans I can use one of the scans for a reference, as I nudge my pieces into place. I put both my new image and my reference scan side by side and zoom in to actual pixel size to make sure I've got my new stitched image as close as possible.




Once I get my pieces aligned as best as I can, I have to deal with a very noticeable seam. This seam must be due to color variations in the two scans. The edge of one scan appears to make a shadow on the other. I can fix this with the handy eraser tool. I click on the eraser tool in the toolbox, adjust it to the size I want and set the opacity to 50%. I then drag my eraser along the seam of the upper layer several times to blend it with the layer beneath. This works amazingly well!




You can zoom in to the actual pixel size to make sure you've really got it blended well.




Once I have erased my seam, all I have to do is crop my new image with the crop tool, and go to Layer > Flatten Image to merge the two layers into one so that it can be saved as a .jpeg and not just a .psd.










And that's it. There may be easier ways to do this with photo-merging software for panoramic photos, but I'm happy with the results I got with the method I used for now.

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