Pls show examples where increasing brightness in post better than increasing ISO.

Started Oct 1, 2013 | Discussions thread
boardsy Senior Member • Posts: 2,215
My example!

Copy/paste from Open Talk > "ISO is a polyseme" thread:

It seems that I previously had not realised a few basic things about photography:

1) exposure is just the amount of light hitting the sensor (or I suppose more correctly, read by the sensor?) from a combination of shutter time and aperture size - regardless of ISO selected. This is not an esoteric scientific definition that doesn't affect us, nor a debatable philosophical or language definition - it's simply what happens every time you take a photo!

2) ISO is not a boosting of the sensor's sensitivity, nor of the registered light "signal" received in either analog or digital terms, as I and apparently others previously believed. It is a re-mapping of the exposure information (see 1) above) after the photo is taken, to affect the viewed brightness of the JPG, and/or a re-setting of the RAW so that the mis-named "exposure" (=brightness) slider's 0 setting is now higher than the original exposure, making the RAW appear brighter in your RAW processing software.

3) "High ISO noise" is not due to an ISO gain/boost, which doesn't actually happen - see 2) above - it's due to under-exposure which is due to less light available (from the lighting conditions, or from shutter time or aperture settings). There was a lower signal to noise ratio on exposure, and subsequently on increasing the brightness (either by high ISO setting or boosting "exposure," brightness, levels etc in software, which all amount to the same thing) there is less information in the shadows to "turn up" so the viewed image falls apart (= "ISO noise"). Fewer bits of data are presumably being used across a larger range of the brightness spectrum (these terms may be making Bobn, GB & DM cringe by now. I hope they are at least notionally correct!).

4) Another consequence of raising ISO to influence the exposure (= shutter time & aperture) is the increased likelihood of blowing highlights to compensate for better shadow exposure. If that's a good compromise for the conditions and your desired result, fine, but it's often safer to under-expose at low ISO and carefully raise shadows later in RAW if you value your highlights.

I applied this "theory" on Monday taking this:

View: original size

Instead of raising ISO to "get a better exposure at the expense of some ISO noise" as I mistakenly would have previously in A mode, I used S mode, kept ISO at base (200 on my camera, a NEX F3), set my aperture at f2 (manually on a Canon FD 35/2 with a Lens Turbo "speed booster" focal reducer adapter lens), and used I think 1/30 second shutter time (as long as I could get away with hand-held), and accepted the under-exposure. This kept the highlights intact and allowed me to massage the shadows and overall brightness in RAW. Yes it's a bit dark, but it reflects the scene and is clean enough.

This is a practical example of how understanding what exposure and ISO really are can help your photography! I thank Bobn and Great Bustard for persevering with this, and I hope that I have understood correctly!

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