Resizing Images for a Digital Photo Frame

My wife recently returned to work after a year of maternity leave. I figured that she might miss being home with me and our son, so I bought her a digital photo frame for our anniversary. To seal the deal, I dug back through all of our digital photos and selected a few hundred that I felt best represent the different stages of our relationship.

The frame that I chose is pretty bare bones. After some shopping, I settled on the Aluratek ASDMPF09. It’s a 10″ frame with 4GB of internal memory and a 1024×600 pixel display.

Probably don’t buy one of these. The only redeeming thing about it is that it is incapable of connecting to the internet. God knows what a shit show that would be…

There’s not much to this device, but while researching, I found that the market leaders in this sector have gone full Internet of Shit in their offerings – Every device comes with a web service, cloud storage, and an email address. Some even require an internet connection to operate. And so I chose to stick with the low tech model in hopes of a better, more secure product, albeit with fewer bells and whistles.

What I didn’t bank on was this device’s absolute inability to rotate and resize images at display time. Here’s an example of what I mean:

The image on the left is the original. On the right, you can see the image as displayed on the digital picture frame. The colour, contrast, and pixelation is the result of taking a photo of the digital frame’s display. These artifacts aren’t present in person, but the horizontal squishing is, and it looks god awful, particularly on pictures of people.

At first, I thought that the problem was the height of the image. I figured that the frame was removing horizontal lines from the image to resize it to fit on the 600px tall screen. Perhaps in doing so, it decided to remove the same number of vertical lines from the image, causing it to look unnaturally squished in the horizontal direction. That would be stupid, but also understandable.

I tried to solve for this by resizing the source image such that it had a maximum width of 1024px and a maximum height of 600px, all while respecting the aspect ratio of the original image. In practice, this meant that the resulting image was either 800x600px or 600x800px, depending on its orientation.

Unfortunately, this did not solve the problem.

After a bit of digging, I remembered that older iPhone cameras used to save time when taking photos by writing files to storage in whatever orientation the phone happened to be in when the photo was taken. To compensate, they added an EXIF attribute to the file to indicate that the photo needed to be rotated at display time. Most devices, including Windows, implicitly handle this reorientation and you never notice that it’s happening. The digital photo frame that I purchased tries and fails, leaving the image stretched in nasty ways that make it look unnatural.

We can see this EXIF re-orientation magic happening in practice by running one of the affected photos through Phil Harvey’s excellent ExifTool. It spits out all of the metadata associated with the photo, including this attribute that instructs the display device to flip the image upside down:

Orientation: Rotate 180

To solve the problem, I can rotate the image such that the EXIF attribute is no longer necessary, and then remove that metadata so that the digital frame does not try to modify the image on the fly at display time. I actually wrote up a solution to this problem way back in 2016 when WordPress did not properly handle the issue. If you read that post back in the day, the rest of this one is going to look eerily familiar.

Then as now, the solution is to sprinkle a little bit of ImageMagick over my photos, resizing them to the dimensions of the digital photo frame while retaining their aspect ratio, re-orienting them as necessary, and stripping any unnecessary EXIF metadata along the way. The end result is an image that the device does not have to resize or rotate at display time.

With a little bit of help from StackOverflow and the folks on the ImageMagick forums, I figured out how to do all of this in a single command:

magick.exe convert -auto-orient -strip -geometry 1024x600 input.jpg output.jpg

This operation is pretty straightforward. Let’s break it down into pieces:

  • convert: tells ImageMagick that we want to modify the input image in some way, making a copy in the process
  • -auto-orient: rotates the image according to the EXIF Orientation attribute if present, effectively undoing the iPhone’s laziness
  • -strip: Removes any unnecessary EXIF data, including the Orientation attribute that is no longer required to correctly display the image
  • -geometry widthxheight: allows us to specify the desired width and height of the output image, in this case 1024×600. By default, this option preserves the input image’s aspect ratio
  • input.jpg: is the path to the file that we want to resize
  • output.jpg: is the path to write the resized image to. Note that this operation will not modify input.jpg

One thing that you’ll notice is that this command only resizes a single photo. Since I have an entire directory full of photos that I need to process, it would be ideal to batch them out. Unfortunately, ImageMagick’s convert utility can only operate on single files. No matter, though – I’m on Windows, so I can wrap the operation in a Powershell command that enumerates all of the files in the current directory and pipes each filename into the ImageMagick convert command for processing:

Get-ChildItem -File | Foreach {magick.exe convert -auto-orient -strip -geometry 1024x600 $_ resized\$_}

You need to run this operation from within the directory that contains all of the images that you want to process, since the Get-ChildItem -File command lists every file in the current directory. We pipe that list into the Foreach command, which loops over every file in the list, substituting its name in for every instance of $_ in the {} braces that follow.

The result is a resized and correctly oriented copy of every image, each with its original filename, all in a directory called resized that resides within original directory of images. One nice side-effect of this operation is that the 300 or so photos that I wanted to put on the frame shrunk in size from 1.7GB to around 80MB. That’s means that I can put significantly more photos on the device than expected, which is a bonus.

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