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A discussion started in another thread (here), and rather than further polluting that thread I thought I would start a new one.
The question for me is whether ADL has any impact on the actual raw data other than reducing the auto-exposure.
I set up a high contrast subject, and shot it twice:
1) With ADL set to high, and auto-exposure in aperture mode with auto-iso off. It chose an exposure of 1/40th of a second.
2) Without changing anything else, I turned ADL to off, mode to manual, and set exposure to 1/40th.
I then imported the photos and looked at the preview of the results (the jpg preview in the file, which is what I see on the LCD). I got this:
The image on the left is with ADL off, the one on the right is ADL on. You can see how in post-processing in camera, the ADL caused the shadow to be raised. Not really shown (since I explicitly forced the next exposure to be the same) is that it also reduced the exposure so as to protect highlights - most of the shade is not truly blown, certainly in raw. If I had turned ADL off and left auto-exposure set it would have used a longer exposure than 1/40th and blow out the shade worse.
To be clear, this difference is in Photo Mechanic which uses the embedded preview. Imported into lightroom there is no difference in the preview lightroom shows, as it ignores the ADL.
But all that is well understood. What I was after is to know if there was any change in the raw image. I then pulled these into photoshop with zeroed ACR settings. They looked nearly identical, so I put them in layers, let photoshop align the layers, and did a difference.
Aside and example: For those who have not used layer arithmetic, doing a difference in two layers causes any identical pixels to zero out (it literally subtracts the pixel values of one from the other). Non-identical portions appear as various colors and patterns that represent the difference. Here's an example in two consecutive shots at a baseball game:
See they are similar but not identical. Layer and subtract and you get this:
Notice most is black - the background did not change. The far left and right show the field of view shifted, as you see a regular image (subtracting to negative flips the sign so you still see the regular image).
Notice the players moved, the ump ever so slightly, the other two quite a bit. Any different jumps out at you. You can brighten it to show subtle changes.
Anyway, back to the ADL example, here's what it looks like subtracted:
The parts around the outside show the camera shifted a tiny bit. The black in the center says "mostly identical". But not quite, necessarily. A difference may be imperceptibly small, so I increased the exposure uniformly by 5 stops. 5 stops is 32 times the brightness of course, so any brightness difference now should jump out as 5 stops brighter:
Still darn close to nothing. I'd argue 5 stops is way beyond anything noticable in the final result. But just to see what I can get (and in photoshop unlike lightroom you get more than 5 stops), here's 10 stops (1024 times the light):
The difference now is visible, but in a specific place -- it's light coming in from outside, reflecting across. My guess is the partly cloudy day had a slight change in light (remember these changes are hugely amplified).
Nothing here would seem to indicate that there's any difference in the raw bits due to ADL.
The question for me is whether ADL has any impact on the actual raw data other than reducing the auto-exposure.
I set up a high contrast subject, and shot it twice:
1) With ADL set to high, and auto-exposure in aperture mode with auto-iso off. It chose an exposure of 1/40th of a second.
2) Without changing anything else, I turned ADL to off, mode to manual, and set exposure to 1/40th.
I then imported the photos and looked at the preview of the results (the jpg preview in the file, which is what I see on the LCD). I got this:
The image on the left is with ADL off, the one on the right is ADL on. You can see how in post-processing in camera, the ADL caused the shadow to be raised. Not really shown (since I explicitly forced the next exposure to be the same) is that it also reduced the exposure so as to protect highlights - most of the shade is not truly blown, certainly in raw. If I had turned ADL off and left auto-exposure set it would have used a longer exposure than 1/40th and blow out the shade worse.
To be clear, this difference is in Photo Mechanic which uses the embedded preview. Imported into lightroom there is no difference in the preview lightroom shows, as it ignores the ADL.
But all that is well understood. What I was after is to know if there was any change in the raw image. I then pulled these into photoshop with zeroed ACR settings. They looked nearly identical, so I put them in layers, let photoshop align the layers, and did a difference.
Aside and example: For those who have not used layer arithmetic, doing a difference in two layers causes any identical pixels to zero out (it literally subtracts the pixel values of one from the other). Non-identical portions appear as various colors and patterns that represent the difference. Here's an example in two consecutive shots at a baseball game:
See they are similar but not identical. Layer and subtract and you get this:
Notice most is black - the background did not change. The far left and right show the field of view shifted, as you see a regular image (subtracting to negative flips the sign so you still see the regular image).
Notice the players moved, the ump ever so slightly, the other two quite a bit. Any different jumps out at you. You can brighten it to show subtle changes.
Anyway, back to the ADL example, here's what it looks like subtracted:
The parts around the outside show the camera shifted a tiny bit. The black in the center says "mostly identical". But not quite, necessarily. A difference may be imperceptibly small, so I increased the exposure uniformly by 5 stops. 5 stops is 32 times the brightness of course, so any brightness difference now should jump out as 5 stops brighter:
Still darn close to nothing. I'd argue 5 stops is way beyond anything noticable in the final result. But just to see what I can get (and in photoshop unlike lightroom you get more than 5 stops), here's 10 stops (1024 times the light):
The difference now is visible, but in a specific place -- it's light coming in from outside, reflecting across. My guess is the partly cloudy day had a slight change in light (remember these changes are hugely amplified).
Nothing here would seem to indicate that there's any difference in the raw bits due to ADL.
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