Abstract: Image and video rendering is an extremely time consuming process requiring a great deal of compute power. This article presents an overview of Arnab Sagar’s application of distributed computing to image processing to expedite the process.
Behind the famed doors of the Walt Disney studio—doors usually barred to all visitors—more than seven hundred artists and musicians worked tirelessly to create their unique experiment in entertainment: cartoon animation. Animatio, the latin word meaning ‘to give life to’ is the apt idea that captures the essence of the end result.
First an illustrator would render the scene and the characters, usually in black and white pencil or charcoal on paper. Next, transparent celluloids were painstakingly painted frame by frame by seasoned experts sitting side-by side in the studio. This work requires that the grayscale imagery from the original renderings are brought to full colour depth with just the right hue. It is vital to be consistent so that the end result appears smooth and realistic. That is, as realistic as a cartoon needs to look!
Today, simple off-the-shelf technology can be used to adjust colour and hue. As proof, an intern at Distributive, Arnab Sagar set out to do just that. Unlike the Disney studios, he uses a digital video that already exists: a close-up moment with a monarch butterfly. The process involves extracting the frames one at a time and converting the frame colour information into numbers (a typed Uint8 Array, specifically) for each pixel. Each pixel of every image is represented by numbers corresponding to colours in the visible light spectrum. Math is done on each pixel to achieve different results. For instance, if you find the average colour value for a given pixel and assign that number to all the colour values, the result is a grey pixel. You will end up with a grayscale image if you do this for all of the pixels in an image. Likewise, brightness and contrast can be adjusted by similarly performing relatively simple math on the pixel colour values.
Of course all this imagery and math takes a lot of time — regardless of whether a human or a computer is doing it. In the case of the Disney studio back in the 1930s, dozens of skilled illustrators worked at desks for long hours to reproduce the perfect celluloid frames, altering colours as well as moving the animation forward. In this way, the labour required to complete the thousands of frames was done in parallel by many people to produce the cartoon drama. It still took months to complete a job that would have taken years by a single artist.
For Arnab, the butterfly frames get distributed using the Distributed Compute Protocol (DCP). Each frame is sent to a separate computer processor to have the calculations performed. Then the frames are sent back and stitched back together in order. Each frame’s array of pixel colour data gets its colour adjusted as a professional production studio would do and the end result is a striking animation with the desired adjustments.
The startling thing about using the DCP is its power and ease of use. In Arnab’s case, two things need to be done: the frames have to be cut apart and assembled into a set of number groups; and, the desired math formula to adjust the colour has to be devised.
Then, with this input set and work function it only takes three lines of code in the javascript environment of any webpage to distribute the work!
People with computer ‘workers’ around the world contribute computing resources to the DCP computing network. A worker can be any computing device including the device you are reading this piece on (thanks for making it this far!). People, institutions and businesses do this to gain computing credits of their own as well as contribute to science and research.
Disney’s Snow White and Fantasia were created by artists sitting at desks in a parallel formation, distributing the work of frame movement animation. Arnab’s animation was transformed using devices working in parallel from around the world enabled by DCP. Disney won academy awards with both of the mentioned projects. For Arnab, the butterfly intern project is certain to win “best short DCP-enabled colour-adjusted video award”. Congratulations all!
—dstewart Q2 22
