I recently had need to print an image I created in Gimp on a Canon Selphy CP910, and encountered more difficulty than I expected. Seaching for solutions on the Internet brought up very little useful information, so I thought I would write a quick note here, and maybe the search engine bots will take a liking to it.
The Canon Selphy is a dye sublimation photo printer that makes 4 inch x 6 inch prints on photo-quality paper. It's very good for printing "snaps" from your digital camera. But if you edit your prints before you try to print, there is a chance the Selphy will refuse to print your image. And to reinforce its stance that you should only print originals, it will advance the ink cartridge, and you will get one fewer print off the cartridge. Money down the drain. Here is one use case that can cause that to happen:
I needed to print a couple head shots for identification. The image had to fit within a 2 inch square, and the face had to fit within a minimum and maximum portion of that square. "No problem," I thought. I could take a couple of head shots with my DSLR, crop and resize them in Gimp, and combine them into one 4x6 image to save on printing. I could even add boxes to indicate where to trim the photos.
A 4x6 photo has an image ratio of 1:1.5. At 300 dpi, that's 1200 pixels x 1800 pixels, so that's the size I created my document in Gimp. After scaling my head shots so they fit within the ID requirements at that resolution, I imported them as layers into my Gimp document, and added nice, red boxes around the head shots to indicate where to cut. Then I exported the composite image as a jpeg, stuck it on an SD card, and went to print it on the Selphy.
"Unable to print photo," the Selphy informed me, as it spit out a blank photo, and advanced the ink cartridge.
Looking for solutions on the Internet, someone suggested that maybe putting the original image's EXIF data in the composite image would help. So I tried that.
"Unable to print photo," said the Selphy, and advanced the ink cartridge.
"Maybe if I use a Windows box to create the image instead of my Linux one?" I thought. I spun up Gimp on Windows and re-exported the image.
"Unable to print photo," said the Selphy, and advanced the ink cartridge.
Then I remembered that some years ago, I created a photo booth out of an old DSLR and a Raspberry Pi. It took multiple photos and composited them together using Image Magick. Those images successfully printed on the Selphy, and were effectively created on Linux, so maybe it was Gimp? I converted a PNG exported from Gimp to a jpeg using Image Magick and tried to print that.
"Unable to print photo," said the Selphy, and advanced the ink cartridge.
I dug up an old photo booth image, and examined its image information. The photo booth image had an image ratio of 1:1.48, so I cropped my composite image in Gimp, and exported it.
Et voila! The Selphy happily printed my image.
Moral of the story: If you want to crop an image, or create a new one on your computer to print on a Canon Selphy (at least the CP910), don't make the image ratio 1:1.5! Other ratios may work, but 1:1.48 works for sure.
