Julia Borg: Low ISO/+EV in PP vs. High ISO in-cam

Started Mar 6, 2007 | Discussions thread
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kocho Senior Member • Posts: 2,690
Julia Borg: Low ISO/+EV in PP vs. High ISO in-cam

Rather than pollute/dillute (?) the UniWB thread even further, I'll post here. And seeing that most folks are lazy to try it and rather have someone else do it, I did it

Here are roughly stated the hyphoteses as I understand them from that uniwb and some other threads say:

(1) A low-ISO underexposed shot, if pushed-up in post processing to match the exposure of a well exposed high-iso shot will produce results similar or better in terms of shadow noise compared to the high-iso shot.

(2) A low-ISO overexposed shot, if pushed-down in post processing by the same amount as a similarly overexposed high-iso shot will preserve the highlights better than the high-iso shot.

I wanted to see it this is what I would get myself. For the impatient, here is my conclusion:

  • on #1: "Properly exposed" ISO400 and ISO800 shots look similar enough to the +2/+3 EV post-processed ISO100 shot to matter to me. Decision which ISO to use should be based on other factors, such as shutter speed/DOF desired.

  • on #2: No observable difference in highlight recovery b/w ISO100 and ISO800. DR is indeed decreased due to the higher noise level, but since the highlight range seems similar at low or high iso, then which one to use should be based on the shadow noise effect and the need for shutter speed/DOF.

Now the question is did I test it right?

Here are the test goas to match the two statements above:

(1) See if adding +EV in Post Processing to an underexposed low iso shot improves anything compared to a properly exposed High ISO shot, with respect to noise and detail retention.

(2) See if adding -EV in PP to equally overexposed low-iso and high-iso shots would make any difference in highlight recovery.

(3) Do it with the software I use (rather than with Julia's "magic" low-noise RAW converter).

Test #1
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Part A*

Setup: Shoot at ISO100 and ISO400 (Nikon Capture NX only has 2EV compensation range in each direction).

Observation: I see a little more noise and slightly more detail in the ISO100 shot.

Part B*

Setup: Shoot a ISO100 and ISO800 shot and use +3EV in Photoshop Elements 4.0 (no NR in ACR, nothing on "auto" - same settings for ACR).

Observation: Slightly more noise and about the same detail in the ISO100 shot

Examples (100% crop from RAW, Capture NX, saved as "good quality"):

ISO400 "properly" exposed, no adjustments:

ISO100 2-stop underexposed then added +2 EV:

ISO800 "properly" exposed:

ISO100 3-stop underexposed then added +3 EV:

Test #2
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ISO100 vs. ISO400, both overexposed by 2 stops then negative 2 EV applied. Observation - a little more noise in the ISO400 shot, no difference in highlight recovery.

ISO400

ISO100

ISO100 vs. ISO800, both overexposed by 1 stop then 3 stop negative EV applied in PSE 4.0 to better show the highlight retention/loss. This is a 400% crop! Left is ISO800, right is ISO100. Observation: more noise at ISO800, no difference in highlight recovery.

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