Super-Nicko wrote in post #6211217
Wim and Robert - I was thinking about this the other day and wondering- how long until part of the metering system will be to detect light and dark areas (which it does already) and to just increase the sensors sensitivity in the dark areas and decrease it in the light areas to give a multi ISO image with combinations that will give a more HDR image.... i mean i dont mind if part of the image is ISO 50 and another part is ISO 800 - i can handle a bit of noise ninja to fix anything up -
I know this isnt the low cost suggestion you were speaking of Robert - it was just something thats been on my mind for a little while and this thread sorta goes the same way... i may be way off with how a sensor works but ah well -
The photo sensor in the camera is comprised of millions of individual photo-receptor sites, each of which provides a numeric value representing the level of brightness at that site (pixel). All matters of scale, dynamic range, ISO sensitivity and noise are applicable to all of the individual photo-receptor sites as a group.
The ISO setting can be thought of as an automatic gain control (AGC), or automatic volume control (AVC) for the overall photo sensor which ultimately determines the sensitivity characteristics insofar as the level of brightness required to register the highest possible output value of the individual photo-receptor sites (pixels), namely, the value 255. When the ISO setting is low, e.g. 50 or 100, it takes a very bright scene to register values as high as 255. Conversely, when the ISO setting is high, e.g. 1600 or 3200, it requires very little light to register values at the maximum of 255.
When the user configures his camera for a given ISO sensitivity, he is establishing that sensitivity as being applicable to each and every photo-receptor over the entire photo sensor, all at once.
If it were practical to provide a separate AGC function for each photo-receptor site individually, such that the "gain" for each photo-receptor site was individually adjustable automatically, as it were, then the overall photo sensor would be capable of automatically adjusting to a wider dynamic range of values.
With the limitations of today's technology, that is not possible, and as was explained above, the ISO setting for a given capture applies universally and uniformly to all of the photo-receptors (pixels). Therefore, unless there is a dramatic break-through in technology, the only way in which the user can control the sensitivity or ISO setting of each individual photo-receptor site separately is to capture another image for each separate sensitivity setting, and that is the basis for "Merge to HDR".
