Writing graphics software gets much easier

A new programming language for image-processing algorithms yields code that's much shorter and clearer - but also faster.

Image-processing software is a hot commodity: Just look at Instagram, a company built around image processing that Facebook is trying to buy for a billion dollars. Image processing is also going mobile, as more and more people are sending cellphone photos directly to the web, without transferring them to a computer first.

At the same time, digital-photo files are getting so big that, without a lot of clever software engineering, processing them would take a painfully long time on a desktop computer, let alone a cellphone. Unfortunately, the tricks that engineers use to speed up their image-processing algorithms make their code almost unreadable, and rarely reusable. Adding a new function to an image-processing program, or modifying it to run on a different device, often requires rethinking and revising it from top to bottom.

Researchers at MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL) aim to change that, with a new programming language called Halide. Not only are Halide programs easier to read, write and revise than image-processing programs written in a conventional language, but because Halide automates code-optimisation procedures that would ordinarily take hours to perform by hand, they're also significantly faster.

In tests, the MIT researchers used Halide to rewrite several common image-processing algorithms whose performance had already been optimised by seasoned programmers. The Halide versions were typically about one-third as long but offered significant performance gains - two-, three-, or even six-fold speedups. In one instance, the Halide program was actually longer than the original - but the speedup was 70-fold.

Jonathan Ragan-Kelley, a graduate student in the department of electrical engineering and computer science, and Andrew Adams, a CSAIL postdoc, led the development of Halide, and they've released the code online. At this month's Siggraph, the premier graphics conference, they'll present a paper on Halide, which they co-wrote with MIT computer science professors Saman Amarasinghe and Fredo Durand and with colleagues at Adobe and Stanford University.