C. David Tobie: Leveraging Phone Photo Artifacts
Feb 2014 04

Imaging artifacts are typically thought of as negative image elements to be avoided. But in phone photography, weaknesses are often turned into strengths, and artifacts are no exception. Let’s take a close look at the iPhone photo below, in terms of how various imaging artifacts add interest and even a bit of mystery to the image.

Overall, the image has been cropped to a square format commonly used in phone photos. The palm tree and church that make up the image subject matter are partial objects, requiring the viewer to complete the image; another technique popular in phone photography. The palm tree in particular is denied to the viewer, though blurring, and by having only a portion of the trunk of the foreground palm visible, and only the shadow of the more distant palm included. So the viewer is engaged to solve the puzzle of the incomplete image. There are other puzzling elements in the image; caused by various types of artificting. Let’s look at each of them.

Let’s start with the palm tree trunk. Phone cameras tend to have a very deep field of focus, so the tree trunk would be only slightly out of focus in most shots. But here the image is taken through the window of a moving taxi, so the trunk also shows a second type of artifacting: horizontal motion blur, increasing the out-of-focus nature of the trunk in a pleasing directional manner that implies motion. Finally, there is rolling-shutter artifacting evident in the tree trunk. If you thought that the tree was growing at a drunken angle, you missed this effect; as the camera scanned each row of pixels in the image, the taxi moved forward, so the rows of pixels from the trunk do not line up, causing the illusion of diagonality.

Lets turn our attention to the façade of the church next. There are sections on the left tower and at the top of the central gable where the masonry is a different color, and where the block seams do not line up with the rest of the building. This looks rather like Trompe l’oeil effects, or sections where the stucco has flaked away showing the actual masonry beneath. However the actual cause of this effect is yet another type of image artifacting: HDR alignment failure. The image was shot in the iPhone’s HDR mode, which composites two images shot in rapid succession, at different exposures. The motion of the taxi caused changes between the two captures, and the software algorithms used to stich the two images together did its best to align the images, but failed, causing these intriguing artifacts on the facade of the church. Other effects, including the ghost window on the side of the tallest tower are also HDR alignment artifacts.

The snapshot-like feel of this image leads the viewer to expect a simple, casual image. Only when the viewer is drawn into the various oddities the image presents does the more complex nature of the shot become evident.

Image shot in Apple iOS 7, processed in NIK Snapseed for the iPhone, with final focus and color checks performed in Datacolor SpyderGALLERY.

C. DAVID TOBIE has been involved in color management and digital imaging from their early development. David has worked to see affordable solutions put in place for graphic design, prepress, photography and digital imaging, and then taught users how best to utilize them. He has consulted internationally for a wide range of color-related companies, and is best known by photographers for his writing and technical editing of texts and periodicals for the photo industry such as Mastering Digital Printing, and Professional Photographer magazine, and his seminars on color and imaging at photographic workshop around the globe. David is currently Global Product Technology Manager at Datacolor, where he develops new products and features for their Spyder line of calibration tools. His work has received a long line of digital imaging product awards including the coveted TIPA award, and a nomination for the Spyder line of calibration tools. Much of David’s recent writing can be found at his photography blog: cdtobie.wordpress.com, and his samples of his photography can be seen at: cdtobie.com.