computer science

Photosynth

Photosynth is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Photosynth rather than just read about it. In short: Photosynth is a discontinued app and service from Microsoft Live Labs and the University of Washington that analyzes digital photographs and generates a three-dimensional model of the photos and a point cloud of a photographed object. Pattern recognition components compare portions of images to create points, which are then compared to convert the image into a model.

Key takeaways

Photosynth belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Photosynth to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Photosynth from memory before moving on to harder problems.

Reference excerpt

Photosynth is a discontinued app and service from Microsoft Live Labs and the University of Washington that analyzes digital photographs and generates a three-dimensional model of the photos and a point cloud of a photographed object. Pattern recognition components compare portions of images to create points, which are then compared to convert the image into a model. Users are able to view and generate their own models using a software tool available for download at the Photosynth website.

History Photosynth is based on Photo Tourism, a research project by University of Washington graduate student Noah Snavely. Shortly after Microsoft's acquisition of Seadragon in early 2006, that team began work on Photosynth, under the direction of Seadragon founder Blaise Agüera y Arcas. Microsoft released a free tech preview version on November 9, 2006. Users could view models generated by Microsoft or the BBC, but not create their own models at that time. Microsoft teamed up with NASA on August 6, 2007, allowing users to preview its Photosynth technology showing the Space Shuttle Endeavour. On August 20, 2007, a preview showing the tiles of Endeavour during the backflip process was made available for viewing. On August 20, 2008, Microsoft officially released Photosynth to the public, allowing users to upload their images and generate their own Photosynth models. In March 2010, Photosynth added support for gigapixel panoramas stitched in Microsoft ICE. The panoramas use Seadragon based technology similar to the system already used in synths. In July 2015, Microsoft announced it would be retiring the Photosynth mobile apps. As Photosynth prepared to shut down in early 2017, Mapillary, a crowdsourced street-level imaging platform, reached out to the Photosynth community with their Photosynth-to-Mapillary blog post, and the official Photosynth Twitter account suggested users "check them out". On February 6, 2017, Microsoft decommissioned the Photosynth website and services. On December 20, 2017, Photosynth returned as a feature of the Microsoft Pix app. In the development of Microsoft Flight Simulator, Microsoft's Photosynth technology returned to recreate buildings and terrain across the entire world.

Process

The Photosynth technology works in two steps. The first step involves the analysis of multiple photographs taken of the same area. Each photograph is processed using an interest point detection and matching algorithm developed by Microsoft Research which is similar in function to UBC's Scale-invariant feature transform. This process identifies specific features, for example the corner of a window frame or a door handle. Features in one photograph are then compared to and matched with the same features in the other photographs. Thus photographs of the same areas are identified. By analyzing the position of matching features within each photograph, the program can identify which photographs belong on which side of others. By analyzing subtle differences in the relationships between the features (angle, distance, etc.), the program identifies the 3D position of each feature, as well as the position and angle at which each photograph was taken. This process is known scientifically as bundle adjustment and is commonly used in the field of photogrammetry, with similar products available such as Imodeller and D-Sculptor. This first step is extremely computationally intensive, but only has to be performed once on each set of photographs. The second step involves the display of and navigation through the 3D point cloud of features identified in the first step. This is done with the publicly downloadable Photosynth viewer. The viewer resides on a client computer and maintains a connection to a server that stores the original photographs. It enables a user to, among other things, see any of the photographs from their original vantage point. It incorporates DeepZoom technology Microsoft obtained through its acquisition of Seadragon in January 2006. The Seadragon technology enables smooth zooming into the high-resolution photographs without downloading them to the user's machine. The Photosynth Direct 3D-based viewing software is only available to the Windows 7, Windows Vista and Windows XP operating systems. However, the team released a Silverlight version of the viewer which has succeeded the D3D viewer as the main option to view photosynths.

Mobile apps As of March 2009, user uploaded Photosynth collections were available for viewing on iPhones using iSynth (3D) or Seadragon Mobile (2D only). The Photosynth application was also available from the App Store to download on iPod Touch and iPhone. In May 2012, Microsoft released a Photosynth App for its mobile platform, Windows Phone. On July 10, 2015, Microsoft announced that they are retiring the Photosynth Mobile Apps, removing them from their stores, and are no longer supporting or updating them. While the Photosynth platform was shut down in early 2017, its features re-appeared in the fall within the Microsoft Pix app for iOS, however as of late 2020, the Photosynth features appear to no longer be part of the Microsoft Pix app.

Capabilities Photographs taken by any regular digital camera or mobile phone could be uploaded to Photosynth. Users had the option to geotag their digital shots on sites such as Flickr and then upload them to the online Photosynth web service. Images uploaded on Photosynth gave people the ability to view landmarks, public spaces and objects from all sides.

Walk or fly through a scene to see photos from any angle Zoom in or out of a photo See where pictures were taken in relation to one another Smoothly change viewing angle between nearby photos Smoothly zoom in and out of high-resolution photos Find similar photos to the one you're currently viewing

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Photosynth

Start with the simplest possible case. Write down what Photosynth claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Photosynth before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Photosynth ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Photosynth

In research: Photosynth appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Photosynth in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Photosynth is common in secondary-school and first-year university syllabi. It links to neighbouring topics 3D graphics software, Discontinued Microsoft software, Microsoft Live Labs, so understanding it makes those chapters shorter.
In everyday life: Look for Photosynth outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Photosynth in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Photosynth means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Photosynth out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Photosynth in simple terms?

Why does Photosynth matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Photosynth?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Photosynth.