Photo Mosaic Android App

Rod Bailey 20 July 2016

Summary

This is an Android application created as a technical exercise for Canva.

The app accepts raw images and produces a mosaic equivalent of them. The tiles of the mosaic can be created in two ways:

• By an external Mosaic tile server supplied by Canva
• Using an internal, simple algorithm supplied by myself.

Switch between these two options by changing the value of Constants.TILE_STRATEGY

The root directory of this project contains a file example mosaics.zip which contains samples of the mosaics produced in both modes of operation.

Design

The app consists mainly of an Activity and a Service. The Activity handles the UI work and the long-running operations associated with constructing the Mosaic image are delegated to the Service. The service does the compute-heavy operations on background threads, leaving the main thread free to keep the UI running smoothly.

Images get into the app by being Shared from some other application on the device, such as a Camera, Gallery or File Explorer app. Photo Mosaic will appear as one of the available destination apps when the user pressed the Share button.

Once the mosaic equivalent of the given image has been generated, it is stored in the public Pictures directory and also added to the Android Media Store.

Finally, the user can elect to Share the mosaic image themselves to some other app on the device.

Concurrency

An essential element of the MosaicService design is the user of parallelism to speed up the mosaic'ing process. Note the use of the ExecutorService to take advantage of the fact that the contents of mosaic tile images can be calculated independently.

TO DO

Being a time-constrained exercise, there are of course a few limitations that are obvious and should be corrected:

• There are several TODO items in the code that point to possible efficiency improvements.
• Circular tiles whose full width or height don't fit in the image's area are squashed into ellipses. This may not be what the client desires - perhaps they want the normal circular tile truncated.
• The UI is very basic and could use some polish.
• A facility to change the mosaic tile size from the built in 32 x 32 would be a good idea.
• A Quick Preview option might be useful. It could be implemented by applying the mosaic operation to the scaled down version of the image that actually appears on the screen.
• I have locked the app to portrait device orientation only, to save time. Landscape should also be supported.