ISO 100, OMD-EM1II and firmware 3.0?

Started 2 months ago | Questions thread
bobn2 Forum Pro • Posts: 61,718
Calling your bluff

Chris Noble wrote:

bobn2 wrote:

Chris Noble wrote:

bobn2 wrote:

katastrofa wrote:

My photos look more noisy when I increase the ISO. Why?

Changing the ISO sets the meter so that you choose to use a lower exposure. Lower exposure means less light energy. Less light energy means fewer photons captured in the image. The signal to noise ratio in the image goes as the square root of the number of photons, so if you capture fewer, you get a lower SNR, which you say is 'more noisy'.

You are mixing changes in exposure vs. changes in ISO setting.

With respect, I'm mixing nothing.

Katastrofa's observation is correct even if the exposure does not change (using manual metering for example). The ISO gain introduces additional noise on top of the exposure noise.

That is simply false. It's provably false with suitable examples, which I've posted here several times, but don't have readily available here (if this conversation carries on, I'll post them again, when I can).

Your explanation below that paragraph is full of errors, but rather than explain them to you, I'll take you up on your offer to demonstrate that you are wrong. Post the same exposure, once at ISO 200 and one at ISO 3200. Don't do any noise reduction or sharpening. Adjust the PP brightness to appear the same on the screen. When you look at the shadows, the error of your understanding will be clear.

So, here are two pictures:

So, what's happened here. These are photos from the same camera (a Canon 60D) 100% crop, taken a few seconds apart with the same exposure. One at 100 ISO, one at 1600 ISO. The raw numbers have been read from the raw files using dcraw, then 'normalized' (i.e. stretched to the same range), in Image Magick, using 64-bit floating point arithmetic (52 bits of precision). Thereafter both shots have been subjected to exactly the same processing, all in ImageMagick, all using 64 bit FP. Essentially, demosaicking, white balance, gamma encoding and output to an 8 bit JPEG. You'll notice the 100 ISO one is much noisier, not, as you predict, the other way round. Having been through this discussion with people like you before, I know you'll raise all kinds of spurious objections, one will be that this is a peculiar camera. So here is the same test with a different camera:

Not as extreme, the D810 is close to ISOless, but what we don't see is what you predicted, the 1600 ISO shot being noisier.

Don't like that?

Here's another

(A note here, Panasonic is doing some WB processing on the raws, not so raw). Anyway, still the !600 ISO version is not noisier. Not enough? Here's a lot more:

The photographer here suffered some shake, doesn't change the noise.

If you really want to continue defending the indefensible, I can provide all of the raw files, just in case you felt like accusing me fo fiddling this somehow (I'm speaking from experience here).

Anyhow, the takeaway is this. In none of these cases do actual results support your supposition that the noise increases with ISO. Time to give it up and stop pretending.

-- hide signature --

263, look deader.

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