[Camera] Automatic ISO always uses an ISO higher than the one needed #25
Description
Tested on Xiaomi Mi2S (13MP), shooting with ISO-auto produces worse photos (with noticeable higher noise) than what is achieved by setting the ISO manually to 100/200/400 according to the scene light.
You can test it by shooting some picture in different light conditions both with ISO-auto and manual ISO forced to a low value. Indipendently from the camera app used, the obtained picture has often the same brightness of the one taken with ISO-auto but much less noise.
Shooting with a low ISO value seems also to trigger a more intensive but useful post-processing work before the image is saved (currently it takes one second to get the image saved instead of the bunch of milliseconds needed with ISO-auto). Maybe, with a low ISO setting, the camera driver captures some burst shots and automatically process them to obtain a single picture (like it does with HDR but with different parameters).
Don't know if this ISO-auto issue is a bad camera driver configuration or is related to some platform settings for camera...