挖掘公共照片，創造美麗的時光流逝

在許多方面，網際網路只是一個極不協調的嘗試，以記錄我們的星球。每天都有數以億計的照片上傳到網上，描繪我們自己、我們的城市、我們的風景和我們的食物。然而，它們也是孤立的、完全不同的：很難從雪崩中篩選出任何有意義的東西。不過，谷歌和華盛頓大學的研究人員找到了一種方法，他們發明瞭一套強大的演算法，可以自動將數百萬張線上照片按時間順序排列，從摩天大樓到冰川，應有盡有。網際網路一端插上電源，另一端則是我們不斷變化...

“我們現在幾乎可以立即創造數千個時間間隔。”

裡卡多·馬丁·布魯拉、大衛·蓋洛普和史蒂文·M·M·沃克寫道：“隨著時間的推移，人們拍攝的數十億張照片記錄了超緩慢的變化。塞茨在一份記錄他們工作的檔案中說而在用數月或數年的時間來建立一個這樣的延時之前，[透過我們的演算法]我們現在幾乎可以立即建立數千個覆蓋地球上最受歡迎的地方的延時。”

<**all>The time-lapses show buildings being c***tructed in Las Vegas. (University of Washington/Creative Comm***) </**all> <**all>They also reveal changes in the natural world, such as the retreat of the Briksdal**reen Glacier in Norway. (University of Washington/Creative Comm***) </**all> <**all>This time-lapse shows the snake-like movement of a sandbank in Thailand over time. (University of Washington/Creative Comm***) </**all>

One of the chief difficulties for the team was synthesizing a single focal point for their time-lapses. Fortunately, the sheer number of images available and our tendency to photograph the same landmarks from the same angles gave them a good starting point. They created a database of some 86 million publicly available photos from sites like Flickr and Picasa and began sorting them; first, creating clusters of different locati*** and then putting these sets into chronological order. For each time-lapse they selected a single reference image that would form the anchor point for the other photos, with their algorithms cropping, aligning, and color-fixing the images to create a single, **ooth time-lapse.

A time-lapse of 1,000 crowd-sourced photos took six hours to process

The team says that in the end they were left with 120,000 clusters, with 10,728 of these containing more than 300 images. From these candidates they selected clusters with more than 1,000 photos to process. "A typical time-lapse with 1,000 input posed photos takes about six hours to compute on a single machine," report the engineers. "While the algorithms can be optimized a lot more for efficiency, we point out that a few hours is negligible compared to the time period of several years it took to capture the photos." The end results are crowd-sourced time-lapses of the changing world, documented almost accidentally by milli*** of volunteers.