We are delighted to publish Jerry Jobe’s latest mobile photography/art tutorial for our viewing pleasure. This time Jobe takes a look at some crucial miscellaneous issues that help will you understand more about some technical aspects to mobile photography. Take it away Jerry…(foreword by Joanne Carter).
“While I generally write articles about how to operate an app, along with articles about how to achieve a certain look, I will sometimes get drawn into discussions of a more general nature. When Snapseed introduced the ability to Export images in the PNG format, as well as the ability to edit RAW files, it drew me into a discussion on file and image sizes that I thought would make a good article. I also wanted to talk about some added features of Snapseed and Over, and those will be discussed at the end.
First, let’s talk about the size of a file. This is how much space it takes up on your device. All image file formats (JPG, PNG, BMP, TIFF, GIF, all the RAW formats, etc.) compress the data in some way so that the files are not enormous. JPG, the most common file format, offers several levels of compression, but the act of compressing the files loses some of the information. JPG is a lossy format. Lossy compression means that if adjacent pixels are similar enough, they are considered to be the same. When recreating the image from the data, these similar pixels will now be identical. Smooth gradients become stripes through file compression.
PNG format can result in either a lossy or lossless compression. Snapseed’s new Export format is a lossless PNG. It means the PNG will be a large file, but there is none of that “striping”. However, a Save or Save As in Snapseed will not result in a PNG, but in a JPG as always. That is because Snapseed wants you to be able to modify the edits you’ve made after saving the file, so they save a JPG and a “sidecar” file, an additional file with edit information.
Some people can see the effects of compression easily, even without the destruction of large areas of smooth gradients. These people are very concerned with the file compression that takes place with the different formats, and are willing to sacrifice space on their device as long as they can avoid compression “artefacts”. I am not one of these people. Some visual destruction that I can see easily has to do not with file size, but with image size – the pixel dimensions of an image.
Each pixel in your image is a square. When you resize an image downward – say, a 3952×2960 to a 2048×1533 – then pixels have to be discarded. Detail is lost. When you resize an image upward, pixels have to be created. This results in the “jaggies” – a smooth line becomes jagged, like stair steps. Why is this? Imagine a single white pixel on a black background. To us, it looks like a dot – it has no shape. But it is actually a square. Now, imagine that we resize the dot from 1×1 to 2×2, an increase from 100% (original size) to 400%. Now that there are four square pixels grouped together, it becomes obvious to us, just by looking, that we have a square. At a lower size, that square could be a circle, a curve, a smooth edge – but as you make it larger its square quality becomes obvious.
There are computer algorithms that try to compensate for the “jaggies”. One of the best is on the desktop, in a program called Genuine Fractals (now bundled with On1 Software as Resize). There does not seem to be anything comparable on mobile devices. When I want to resize an image, I use Big Photo, an app I covered in part a few years ago. The interface has changed somewhat, so let’s cover the entire app now”.