Just a quick note: the "partially shaded border" is much less shaded on images taken with zoom. It exists because vignetting correction is not applied to the border area.
Quote from: srsa_4c on 31 / August / 2014, 17:27:48Just a quick note: the "partially shaded border" is much less shaded on images taken with zoom. It exists because vignetting correction is not applied to the border area.So some (but not all?) of the vignetting correction is applied to the raw? I vaguely remember something about this in one of Stick's threads.
This is the first time I have heard a suggestion that some processing is applied to the sensor data prior to CHDK capturing it. Seems a bit strange.
Can this thing whatever it is be identified / maybe even get its own override in the future?
There are event procedures with names like SetSensorPreGain, SetCDSGain, SetCDSGainStep (etc.), which may indicate multiple sensor gain related hardware.
- take a cam and override Exposure time, ISO and ND-Filter/Aperture- take two DNG photos of an evenly lit surface (e.g. white screen portion, out of focus) - 1) zoomed out - 2) zoomed inI took SD850 @5.8mm and 23.2mm. The lens has a printed label saying that it's aperture is 1:2.8-5.5. One would thus expect the zoomed in photo to be ~1.5 times darker in terms of linear intensities than the zoomed out. It is not. The two photos seem identical in terms of intensities reaching the sensor. They can't be.
If you overrode shutter speed, aperture, ND and ISO, then both images should be the same - you've taken two images with the same exposure settings so you should get the same result.
Quote from: philmoz on 31 / May / 2018, 21:04:14If you overrode shutter speed, aperture, ND and ISO, then both images should be the same - you've taken two images with the same exposure settings so you should get the same result.If the lens were a fixed aperture design yes but it's not. @5.8mm it is f2.8 @23.2mm it is f5.5 - let's say f5.6 for easy factors Zoomed out it lets ~four times as many photons reach the sensor as zoomed in. If you override shutter speed, aperture, ND and ISO that should show. It doesn't the image stays as bright. We established way back when that that's due to another amplification factor, that is not ISO but combined with it seems to control the actual pre A/D conversion analog gains. Where srsa_4c pointed to items like "SetSensorPreGain" in the event procedures. The amplification of noise in fully covered sensor areas demanded such an explaination.
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