How can I do an HDR image?

Is it technologically possible to perform real "multi-image" HDR photography with a single shutter press?

• The question is a little ambiguous, so let me be more explicit: Typical HDR photography seems to involve taking 3 pictures at various levels of exposure, and composing them. Let's say we do this by using three different shutter speeds, e.g. 1/120, 1/160, 1/200. In theory (assuming various technologically feasible tweaks to camera design), could we instead do this by telling the camera to take a single photograph at 1/120, but to "peek" at the image sensor data at the two other relevant times (1/200 and 1/160), thus enabling three differently-exposed images to be extracted? Is there enough data transfer speed to support something like this? The hope would be to enable rich HDR photographs using only one shutter press, thus avoiding some of the logistical limitations of HDR.

• Answer:

  Yes this is possible. In fact, you don't need to take three images with most modern HDR software, as long as you are shooting RAW. No need for your fancy system. A RAW image has a greater dynamic range than any display can achieve. The darks and highlights can be tone mapped just out of the highs and lows of the RAW's data. You can even get most of this effect from a RAW converter that allows control of curves and controlling of the Shadows and Highlights levels. But, it won't be as rich. Shooting a full stop or two up and down from the normal exposure value gives you an even greater dynamic range, allowing for a richer, much more detailed HDR image. The problem with the system you are describing is that the process for collecting some information from a pixel sensor and then some more information later in the exposure won't work. Collecting the data from the pixel sensor also wipes that data from the sensor. Your "peeking" is effectively recording an entire image from the data so far and then the sensors are reset, empty of data. The reason we use shutters is that the measurement of the exposure time is much more accurate as the high speeds than mirrorless cameras. But, if you just want to avoid the delay of flipping the mirror up and down and actuating the shutter, then I suggest you use a micro four-thirds camera which has no mirror and (possibly no shutter as well) and would shooting all three of those images without pause, just as you described.