"...there exist disadvantages to the process of generating a HDR image from multiple independently captured images. For example, changes may occur when images are captured successively such that a composite HDR image generated therefrom may not be completely aligned. This may generate motion artifacts in the composite HDR image. Further, the images may be affected by local motion in the image scene, e.g., trees swaying in the wind, people and faces shifting slightly, etc. Additionally, the time required for a HDR image to be processed may be delayed based on the images to be captured."
So, the solution is to read same row several times, each time with different exposure. Then the several reads are combined into a single HDR row in an image processor:
"To generate a HDR image during a single exposure of the frame (i.e., fixed amount of time t during which the rolling shutter reset 80 moves across a frame), multiple reads of the same row of pixels of the image sensor may occur. For example, a first data read 86, of the data stored in a row of pixels, may be undertaken at a time n, where n is a fixed fractional time of time t. This time n may be, for example, 1/2, 1/3, 1/4, 1/5, 1/10, 1/20, or another value of the frame time t. This time n may be represented as line 88 in FIG. 5. That is, the first data read 86 may occur at a time n subsequent to the reset of a row of pixels by the rolling shutter reset 80.
Accordingly, as the rolling shutter reset 80 passes downwards along line 78, the first data read 86 may trail the rolling shutter reset 80 by time n. In this manner, data stored in the pixels for each row of the frame may be read at a time n after the rolling shutter reset 80 of that row of pixels. Thus, each row of pixels read as the first data read 86 passes across the image sensor will have been exposed to light for the same time n, which may be referred to as an exposure time or integration time."
While the exact reference escapes me, I've heard about a similar technique being used by a major security camera vendor for more than 10 years now. It might be new in a smartphone world though.
While we are at Apple, Terry Gilton, Senior Director of Sensor Technology at Apple, posted a note on his LinkedIn page:
"I am seeking some more ultra-motivated, highly innovative sensor engineers. Some opportunities in characterization, validation, analog design, and architecture of all kinds of sensors. If you are passionate about sensing stuff and feel like you want to change the world, let me know."
