ISO & Dynamic range - what is going on?

the NR was applied in PP photoshop and topaz. as i keep saying noise reduction does not increase DR period. the cap clearly shows this.

old age reduces hearing DR 😁 i wound up an old watch the other week and had to ask my daughter if she could hear it ticking and she said clearly , i couldnt 😌

Dolby D = Dud, it was all marketing, I owned an electronics repair shop back in the 70s and repaired many a cassette deck including hi end Disco consoles where the finals cost $120 back then, one guy had gone through 4 pairs and they kept blowing till i discovered that the drivers where over biased so i just turned them down a little and job done 😎 they were the good old days, audio sig generator, RF sig generator, 4in osiliscope and a frequency counter ,couple of hand made lodgic probes and away you went including transceiver repairs and modifacations. and a good 3v mini scope instant iron.

But the Exposure slider doesn't alter exposure, it's just named "Exposure" and only adjusts the brightness, modifies the way the data is displayed. How do you know that it doesn't weight the adjustment or add a perceptual intent?

Also, again you're looking at an RGB computer screen post conversion to your chosen colour profile. The DR of the screen if fixed. So it's not possible to observe a higher DR in any file directly. All you're doing (paradoxically) is compressing the DR in the RAW until it fits within the fixed DR of the screen. That's basically what the basic sliders do, stretch and compress the data so you can make it fit into the fixed DR of your output device with pleasing colour and contrast.

I'm not quite sure what it is you think you're doing.

noise reduction is no different than veiling glare, veiling glare reduces DR period, you have the equipment do the test to back your claims.

Hi All

Just arrived at this thread after a while away. I have to say my impression of the thread is spoiled by Donald's belligerence, arrogance and dismissal of useful and educational posts. I'm sure Donald has useful things to say, but adoption of a politer and more humble approach would significantly improve the attractiveness of this thread and be very welcome. That's my contribution to the interpersonal stuff :-)

Now, to the thread itself...

The way that digital sensors work means that the most critical factor if you are aiming for a conventional technically high quality image is highlight exposure. Fully clipped highlights are unrecoverable so it is the photographer's responsibility to ensure that important highlights are not clipped (we can let specular highlights go).

Assuming the exposure has been pulled off to preserve the highlights, the dynamic range is then determined by how much noise there is in the dark tones. This is a subjective judgement, some people can tolerate more noise than others and so will enjoy a wider dynamic range than others. But at some point the noise levels will be so high and the colour/tones so damaged by the noise that no one will accept it in their images. This must surely represent the noise floor for any photographically useful image.

Where noise reduction has been applied to the darker tones and reduced the noise in those tones, allowing us to make use of darker tones without the horrors of excess noise and without being forced to clip them to black to hide it, it is entirely reasonable in my book to claim that dynamic range has been improved.

About noise: Noise can roughly be split into read noise (added by the electronics and added after ADC) and photon shot noise (which is a characteristic of the quantum nature of light and happens at the point of capture before ADC).

The reason why analogue gain (aka increasing the iso setting) can be useful is because it (in some cameras) amplifies the signal. Because read noise is added post signal amplification this means raising the ISO boosts the signal before read noise is added, reducing the ultimate proportion of read noise at the end. However, amplification does not reduce photon shot noise because this exists at the beginning and therefore gets amplified along with the signal. The final values have equally boosted signal and shot noise. Modern cameras tend to have low read noise compared to early cameras, so boosting the amplification doesn't gain you as much in reducing read noise as it used to. These days photon shot noise is the key player and the way to control that is more exposure.

It's also worth bearing in mind that because boosting amplification drives the highlights into clipping quicker, you also lose highlight dynamic range when you raise ISO, which means the improvement in shadow noise might make the image look nicer, but you ultimately lose overall dynamic range.

The dual gain thing has always been a bit of a mystery to me, the info about using a capacitance change to reduce the sensor sensitivity and therefore to allow more exposure (which reduces photon shot noise) is very helpful (assuming I have understood what has been explained).

On the uneven DR plot, Canon were notorious for messing about with exactly how they implemented ISO settings years ago, particularly the settings in between full stop increases. I'm not entirely surprised to see unevenness in performance at different ISO settings as a result.

There's a parallel with Sigma-Foveon cameras in their low-res raw capture. On-sensor, pixels are binned 2x2 connecting the outputs of four pixels together in parallel. The effect of that is, for a given exposure, four times the current goes into a four times bigger capacitor resulting in the same voltage output from the now big pixel which is the average of the previous four pixels.

P.S. Shot noise is also reduced.

Read noise, in the context of imaging and electronics, refers to the noise introduced during the process of reading out the signal from an image sensor, like a CCD or CMOS sensor. It's essentially random fluctuations in the electronic signals that represent the image data as it's being converted from analog to digital.

Why the different lenses and focal lengths, for the same lens mount? The right-side image has color fringes (red and blue) in the specular lights on the cornea, and the left-side image does not. Obviously the lenses and/or different processing are playing roles here; not just different pixel densities. Also, you lose the guarantee of equal exposure when you use different optics, especially at low f-numbers like 2.8, where the actual transmission varies wildly with different lenses. Also, at f/2.8, most zoom lenses have much more aberration than diffraction, and so total blur will be different. The focal lengths are different; did you adjust distance, accordingly, for the doll's eye to be the same size in mm on the sensors?

Again, Nearest Neighbor upsampling gives predictable results with the same scene and optics; the larger the pixels, the higher the maximum contrast between neighboring pixelated pixels. If you use a sharper lens with the bigger pixels, then you're going to have even more high-contrast between the pixelation neighbors (horizontal and vertical, only). This is what the primitive levels of our brains look for to feel like we have successfully focused on an object, which can fool us into mistaking this acuity for actual image information.

So, there are just too many wild cards here for your test to have any meaning.

The 2 tamron lens are both equally as sharp as each other i just framed the doll to the correct composition. lens breathing is most likely playing a part in the different focal lengths, its only 5mm 😏, as a guy over in the sony forums has also noticed his a7iv images appeal more over his a7r5, at least he being honest with him self. i just shot identical images from 2 tripod set ups at different iso readings to see when noise started to decreases detail . it starts at iso 320.

It's the key to understanding ISO-invariant (ISOless) sensors.

Modern sensors have been designed to have very low read noise. This means that they do not benefit much (if at all) from raising ISO because there is very little read noise to suppress. Raising ISO (usually, not all cameras' ISO knobs do the same thing) reduces dynamic range because the amplification boost drives highlights into clipping. If it brings no useful read noise suppression, then it is simply a dynamic range destruction knob, and using it is pointless. You will get the same read noise leaving the ISO knob at base ISO, deliberately underexposing and brightening in post. The increase in shadow noise from lifting the shadows will be minimal because the read noise is so low to start with. By leaving the ISO knob alone, you hold on to your highlight dynamic range. This is the ISOless strategy.

In saying this, I don't actually shoot ISOlessly, even though for best image quality I should. The reason why is a personal foible. When I use the ISOless strategy I have found that I regularly let shutter speeds fall too low and lose sharpness to camera shake. Switching to auto ISO and letting the camera vary ISO helps avoid falling into the too low shutter speed trap, even though I sacrifice dynamic range as a result. I have decided that losing dynamic range is less bad than suffering camera shake. But that is a foible, anyone who can reliably remember to keep a good eye on their shutter speeds and adjust settings accordingly would get a dynamic range advantage from following the ISOless strategy (assuming they have an ISO-invariant camera) without suffering more read noise.

p.s.

I'm not an engineer and this is a gross simplification of what read noise is. The details are, frankly, beyond me, and my description lumps several sources of noise into one simplified bucket, but for the purposes of this level of debate, treating it this way gets across the gist.

p.p.s.

If you shoot with a dual gain sensor and want to follow the ISOless strategy, you'll want to modify it slightly into a Two-ISO strategy. Shoot at base ISO for shots where there is plenty of light then switch to the higher gain ISO when you know you will be underexposing a large amount.

p.p.s.

Personally, I'm too stupid and get too excitable under real field conditions to keep all this complexity straight in my head, so good old school auto-ISO works for me, even though I know I am sacrificing dynamic range. Better a shot that 'comes out' than a tuned shot that is broken, as I have figured out from hard experience.

For anyone interested in the technical details which are not all what Alan said:

chatgpt.com/share/6876c085-0750-8013-a408-c6d5451619af