A while ago a talented Verizon salesman sold me an iPad mini 2 that I didn't really want or need. Now that I have it, I thought I might as well load some photos to show off on its pretty screen. I decided to make jpegs specifically optimized for that purpose.
I sync my photos to the iPad using iTunes on a PC.
Because the screen is reasonably wide even in its shortest dimension, I decided to make all my jpegs based on the assumption that the viewer would keep the iPad in its vertical (portrait) position all the time rather than turning it back and forth depending on the aspect ratio of the picture.
The iPad mini 2 screen is 1536 x 2048 pixels, with 326 pixels per inch resolution. This meant that I would make all landscape format photos 1536 pixels wide, letting the height fall where it may. I would make portrait format photos 2048 pixels high unless the width came out to more than 1536, in which case I would make them 1536 pixels wide.
This worked out fine until I discovered an iPad software bug (feature?), which is this: If a picture is pretty close to the same aspect ratio as the screen, the software zooms in to completely fill the frame, cropping off some of the picture, either from the sides or the top and bottom. (How close is "pretty close"? See below.)
This was not acceptable. I crop my pictures exactly as I want them to appear and don't want some piece of software second guessing me. If one double-taps the screen to zoom in on the picture, then double-taps again to zoom back out, the picture is displayed correctly: full-sized, with black bars filling out the unused edges of the screen. But the viewer would have to do this every time for every picture having this issue, which would be a pain in the neck and also not acceptable to me.
I am obviously not the first person to discover this bug/feature. Googling brings up various discussions but no cure that I could find.
The solution for me was to add my own black bars to the edges (left and right or top and bottom) to fill out the whole 1536 x 2048 frame when necessary. And when is it necessary?
By trial and error, I discovered that a picture that's a full 2048 pixels high and 1396 pixels or fewer wide will display correctly. But make it even one pixel wider than 1396, and the software zooms in, cropping the top and bottom of the image.
Going the other way, an image that is 1536 pixels wide and up to 1860 pixels high displays correctly. Any image taller than 1860 gets cropped from the left and right.
So the bottom line for me was this:
Image 2048 pixels high and 1396 or fewer pixels wide: OK as is
Image 2048 pixels high and more than 1396 pixels wide: pad sides with black to make the width 1536
Image 1536 pixels wide and 1860 or fewer pixels high: OK as is
Image 1536 pixels wide and more than 1860 pixels high: pad top and bottom with black to make the height 2048
Of course, one could just pad every image out to the full 1536 x 2048, but that would bloat some files unnecessarily. And anyway it was more fun to figure this out.
