1 stop of DR -how important it is and for what kind of photography

Started Apr 7, 2012 | Discussions thread
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Safesphere Regular Member • Posts: 149
Re: JPEG is limited to 8 stops

DigVis wrote:

Safesphere wrote:

(In the interest of a full disclosure, photons do not exist before the wave function of light actually hits the sensor. So the sensor does in fact quantize light, but not in the sense relevant to this discussion. It is just the weirdness of quantum mechanics.)

I should know better than to argue this point with a physicist, but I am quite sure one could claim that the photon exist at the point of emission too.

Then how would you explain diffraction? Photons not following a straight line while flying?

In quantum mechanics you need to use a different logic. If you have heard that light is a wave and particles at the same time, you have been misinformed by the media. Light is always a wave while it is propagating an is always photons when it is detected. It is the act of detecting that converts the wave into photons and in our case it is done at the photocell. They call it the collapse of the wave function.

If you assume that photons exist at emission, you would have to admit very strange properties of them. For example, if you have a screen with two slits on their way, then each photon would fly throught both slits at the same time. Even if you release them one at a time. I kid you not. Google the double slit experiment by Young.

But if you detect the photons at the slits, you would see that each flies through only one slit. It seems mind blowing, but the explanation is simple. Photons do not exist as particles until you detect them. Again, it is the very act of detection that collapses a smooth wave into a set of particles randomly distributed in the proportion of intensity. Only when hitting the detector does the wave present itself as individual photons.

The same is also true for electron beams in a CRT or for any beams of any subatomic particles.

So let's add random noise to the input signal, and be a bit careful about the design of the noise distribution. Specifically, if we add a uniform random noise ±0.5, we will actually perfectly decorrelate the quantization noise. In this case, the output value of the sensor will be 1 with a probability of x.

It is not clear how you add a negative noise to light, but let's say you present it as a voltage between the photocell and ADC. If your noise is a random number between -0.5 and +0.5, then any signal less than 0.5 would read as zero with the probability of 1, not x. So your example does not seem to decorrelate the quantization noise.

However, if you add a random noise ranging between 0 and 1, then you might be right. Although the real noise might not be limited precisely by 1 and have further truncation effects. This is probably the reason they add the noise of 2 LSB to remove the quantization error.

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