Although the iPhone 4 camera’s full resolution is 2592x1936px, there are still quite a few apps which are unable to take advantage of the camera’s full 5MP resolution.

There are still a lot of apps that only support up to 2MP or 1600x1200px resolution. Saving full-res iPhone 4 images down to 2MP with these apps often results in an image size of 1600×1196 or 1195 pixels. What happens to the missing 4-5 pixels? It’s actually not a bug in the OS or in the apps themselves.

The answer lies in the aspect ratio of the new iPhone 4. The aspect ratio of a photo is the ratio of the width of the image to its height. On the iPhone 4, it’s just a little bit narrower than previous iPhone cameras.

The 2MP and 3.2MP cameras of the older iPhones have an aspect ratio of 1.3333:1. The iPhone 4 has an aspect ratio of 1.3388:1 which is just a hair narrower — and enough to cause a few pixels to drop off when the image is reduced.

Doing the math, if you reduce an iPhone 4 image 61.73% to 2MP, you get an image that’s 1600×1195 — still not 1196, but the math explains the missing rows of pixels. The extra pixel is probably rounded up to maintain an even pixel count. Computers like binary.

The same math explains the six pixel difference when an iPhone 4 image is reduced to 3.2MP and the resulting image is 2048×1530 pixels instead of 1536.

Apps like Mill Colour, FocalLab, NoiseBlaster and others aren’t losing your pixels. They’re simply accurately maintaining your original aspect ratio as they downsample your photos.