Question about image sensor bias lighting.

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Flash of Insight
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Joined: Mon Jul 03, 2017 12:04 am
Real name: Karen Savage

Question about image sensor bias lighting.

Post by Flash of Insight »

I remember a discussion in Anton Wilson's Cinema Workshop book about 'flashing' filmstock to improve the capture of dark detail of the captured image.

'Flashing' consists of exposing the film to a very weak level of light in addition to the image being exposed. The flashing light can be 'white' light – of whatever color temperature the DP chooses or it can have a distinct color cast.

Flashing can be performed pre-exposure; either by use of a contact printer to expose the film prior to loading the camera, or by exposing it in camera by shooting a white or gray card with an ƒ-stop that will give the desired pre-exposure, then rewinding the flashed stock and reloading the camera.

It can be flashed while shooting by shooting through a beam-splitter that 'covers' the image with the desired amount and color of light. Wikipedia:
On-set flashing solutions include Panavision's Panaflasher, which is mounted in between the camera body and the camera magazine throat, and Arri's Varicon, which functions as an illuminated filter and can be viewed directly through the viewfinder for manual setting of the flash level.
Finally, it can be post-flashed at the lab, by exposing it on a contact printer (just like lab pre-flashing,) prior to development.

Since exposure levels increase logarithmically, this tiny level of additional exposure has no practical effect on an image's mid-tones or highlights, while it shifts the darker areas of the image into the practical sensitivity range, thus allowing darker areas of the image to show visual detail rather than uniform blackness.

Flashing can be applied to the film stock before, during, or after principal photography of a motion picture, although always before the film is processed. When applied before or after shooting, this is generally done by a film laboratory. The level of flashing needs to be tested beforehand and subsequently moderated appropriately against the light levels of the scene, or else it risks having minimal impact if too low or making the shadows "milky" when too high.
I remember recently that an article for a new sensor mentioned that the sensor chip received bias lighting from the rear of the chip. I also remember some mention in the earlier days of solid-state sensors that some camera designs provided for 'flashing' the sensor with bias lighting in order to improve the detail rendering in dark areas of the image. However, now I can't find any information on which cameras or chips used bias lighting. (and the word 'flashing' is totally ruined by Rule 34...)

QUESTION: Can you provide information on image sensors that employed bias lighting?
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