03-08-2011, 02:06 AM
[quote name='PuxaVida' timestamp='1299500610' post='6572']
The "twisted color profiles" is an expression Walter pointed out, which is used for standart color profiles of ACR. When I push up exposure in ACR, it's not only the brightness which is adjusted. ACR does other manipulations on the image, and maybe this is why I've seen a big difference between two images with the following exif data:
f/5.6, 1/640, ISO 800
f/5.6, 1/640, ISO 200
On the image with ISO=200, the exposure was pushed up (+2) in ACR to have the same brightness with ISO 800 image (and nothing else was touched). The resulting image was clearly worse than the ISO 800 image in terms of IQ. It has more noise, over-saturated colors with high contrast and also has a less DR.
Serkan
[/quote]
It's difficult to expect a linear outcome when most things aren't linear.
Sensors for example have 3 colour channels (as we know) and all three should have different response curves (efficiency that varies with the amount of light going in). A "decent" amount of light is necessary for the "ordinary" response case that we know of but if the image is underexposed (to be pushed in post later), I'm sure the response will not be mathematically proportional to reduction in actual exposure.
The above will also lead to a change in colors (hue and saturation, regardless of brightness) depending on the exposure (because the 3 channels have independent response curves). So there can be colour shifts depending on the level of exposure and maybe ACR corrects these in a way which results in images that are slightly different to properly exposed shots. Or maybe ACR doesn't correct them at all. Either way, you're bound to see a difference.
GTW
The "twisted color profiles" is an expression Walter pointed out, which is used for standart color profiles of ACR. When I push up exposure in ACR, it's not only the brightness which is adjusted. ACR does other manipulations on the image, and maybe this is why I've seen a big difference between two images with the following exif data:
f/5.6, 1/640, ISO 800
f/5.6, 1/640, ISO 200
On the image with ISO=200, the exposure was pushed up (+2) in ACR to have the same brightness with ISO 800 image (and nothing else was touched). The resulting image was clearly worse than the ISO 800 image in terms of IQ. It has more noise, over-saturated colors with high contrast and also has a less DR.
Serkan
[/quote]
It's difficult to expect a linear outcome when most things aren't linear.
Sensors for example have 3 colour channels (as we know) and all three should have different response curves (efficiency that varies with the amount of light going in). A "decent" amount of light is necessary for the "ordinary" response case that we know of but if the image is underexposed (to be pushed in post later), I'm sure the response will not be mathematically proportional to reduction in actual exposure.
The above will also lead to a change in colors (hue and saturation, regardless of brightness) depending on the exposure (because the 3 channels have independent response curves). So there can be colour shifts depending on the level of exposure and maybe ACR corrects these in a way which results in images that are slightly different to properly exposed shots. Or maybe ACR doesn't correct them at all. Either way, you're bound to see a difference.
GTW