Oppo Find 7 features QHD display and 50MP images59
Several manufacturers were rumored to launch a smartphone with a QHD-display (2560x1440 pixels) at Mobile World Congress in Barcelona but none of the models introduced at the show featured one of the high-resolution screens. Now the wait is over. The Chinese smartphone manufacturer Oppo has introduced their latest flagship model, the Find 7. This makes the Find 7 the first smartphone to feature a QHD screen. The pixel density of the 5.5-inch display is a staggering 538ppi which should make for ultra-sharp rendering of images and text.
Not only is the Find 7's screen top-notch, the new device comes with top-end specifications all around. The Android OS is powered by a Snapdragon 801 SoC and 3GB RAM. Rapid Charge technology will let you charge the Find 7's 3000mAh battery to 75% in only 30 minutes and a MicroSD slot allows for easy storage expansion.
With a 13MP 1/3.06-inch Sony Exmor CMOS sensor and F2.0 aperture, the camera specifications look decent, but not anything out of the ordinary. The Find 7 also comes with a "Super Zoom" software feature that allows for the capture of 50MP images. To achieve this the camera takes a burst of 10 images, then selects the four best shots and combines them into a single 50MP frame. Brief communication with Oppo indicates they are using a 'superposition' technique to create the 50MP file. We surmise the underlying principle is similar to that used by the Hasselblad H4D-200MS to create 200MP images from a 50MP sensor (note the similar 4x increase in resolution over the native sensor resolution). Such super-resolution techniques create a higher-than-native resolution image by relying on small movements from shot-to-shot to allow for high frequency detail - beyond what the sensor could natively represent accurately - to be recovered. For example, consider the following example where the sensor (indicated by the pixels outlined in red) is imaging black lines with widths on par with pixel widths.
Depending on the alignment of the sensor to these alternating black and white lines, the sensor may (left, in the image above) or may not (right, in the image above) accurately represent the original pattern. Remember: a pixel just tallies up the amount of light entering it, and on the right, any pixel is just recording 50% white and 50% black - that is, grey. This loss of contrast - resulting from the pattern being averaged across pixels - results in a decrease in resolving ability of high frequency detail. Now imagine shifting the sensor such that the pixels on the right were to align with the pattern just as the pixels on the left initially did in the example above. This might allow for the recovery of additional detail. Sophisticated software algorithms can 'look' for this sort of detail across multiple shots to increase the effective resolution of capture. Oddly enough, the small movements your hands make from shot-to-shot - which you might initially imagine as deleterious - end up potentially increasing the spatial resolution of the sensor. Simply by allowing for many different alignments of the sensor's pixel grid to the real-world detail being projected onto it. You can read more about the basic principles of super-resolution and how it is used to recover sub-pixel information in Photo Acute software here.
We do note that for this method to be effective, the lower 'native' resolution images need to be aligned with sub-pixel precision. However, with faster processors as well as accelerometer information regarding shot-to-shot movements, we imagine this is not too large an issue with modern hardware.
The 50MP Image - Any Good?
While Engadget shows a sample that does not look too impressive at 100% view and has the appearance of an upsampled file, the technique might have its merits in a phone for creating a better, native 13MP resolution file (downsampled from the 50MP file). Although Oppo confirmed that a lower, 'native' resolution output using their "Super Zoom" technology would not be available (single shot 13MP - including RAW - output is still available), users can always downsample the 50MP file to 13MP in any photo-editing suite themselves. Furthermore, any multi-shot technique has the potential to reduce noise - especially important for the small sensors found in phones.
All that said, given the feature's "Super Zoom" moniker we would expect the large images to, at the very least, be used for a more efficient digital zoom. It'll be interesting to see how it compares to Nokia's PureView and more conventional systems once more samples are available.