CCD is analog?

[j.weegee]

Forgive me if this is common knowledge, but as I was looking into the difference between CCD and CMOS sensors I was surprised to find that CCD sensor is analog. Now maybe this is due to the fact that my find automatically associates the word analog with film, but I am wondering how a CCD chip is analog?

 

[bhop]

I guess..
Talk:Analog photography - Wikipedia, the free encyclopedia

Most people (myself included) would still consider "analog" to mean film.. i mean, you have a strip of film vs. digital file in the end..

 

[fjrabon]

everything is analog until it's converted to digital. Until the sensor goes into the camera's A/D converter, it's always analog. This is the same for CMOS and CCD. The electrical signals created by photons hitting the sensor don't start of as 0's and 1's. Electricity is analog.

 

[unpopular]

In electronics, "analog" refers to a continuous voltage range, rather than a digital "on" or "off" state. Because a photograph measures the quantity of light, not if light is there or not, there is no way to directly measure light digitally. Instead, a digital camera measures light with an analog sensor, one the correlates the quantity of light with a voltage. This is then converted into a digital value using an ADC and recorded.

 

[unpopular]

Electricity is analog.

This is kind of true. Unless it's expressed as a bit. A bit could be any voltage, but not any voltage in between that voltage and whatever voltage represents zero. Provided that everyone agrees, any voltage level could represent either bit.

 

[Kolia]

Analog doesn't really exit !

Quantum physics rules !

Lol !

 

[j.weegee]

That puts so much into perspective. Thanks for the input guys.

 

[fjrabon]

Electricity is analog.

This is kind of true. Unless it's expressed as a bit. A bit could be any voltage, but not any voltage in between that voltage and whatever voltage represents zero. Provided that everyone agrees, any voltage level could represent either bit.

True, but to that extent anything can be considered digital, as long as you agree on what constitutes 0 and what constitutes 1.

 

[unpopular]

Analog doesn't really exit !

Quantum physics rules !

Lol !

Correction: photography measures the likelihood of light being in a particular place or not....

 

[unpopular]

Electricity is analog.

This is kind of true. Unless it's expressed as a bit. A bit could be any voltage, but not any voltage in between that voltage and whatever voltage represents zero. Provided that everyone agrees, any voltage level could represent either bit.

True, but to that extent anything can be considered digital, as long as you agree on what constitutes 0 and what constitutes 1.

Yep. Digital is a means of communication using two, and only two, predetermined states. It could be described as amplitude (voltage), phase, frequency, position or any other measurable quality that can be compared against some other quantity.

But it's not digital until the quality represents something.

 

[fjrabon]

This is kind of true. Unless it's expressed as a bit. A bit could be any voltage, but not any voltage in between that voltage and whatever voltage represents zero. Provided that everyone agrees, any voltage level could represent either bit.

True, but to that extent anything can be considered digital, as long as you agree on what constitutes 0 and what constitutes 1.

Yep. Digital is a means of communication using two, and only two, predetermined states. It could be described as amplitude (voltage), phase, frequency, position or any other measurable quality that can be compared against some other quantity.

But it's not digital until the quality represents something.

yeah, in a manner of thinking all an A/D converter is a machine for applying the agreed upon choice to the signal and then turning it into another signal where all information except the 0 and 1 is lost.

 

[Kolia]

Correction: photography measures the likelihood of light being in a particular place or not....

Aha ! Yes !

 

[unpopular]

True, but to that extent anything can be considered digital, as long as you agree on what constitutes 0 and what constitutes 1.

Yep. Digital is a means of communication using two, and only two, predetermined states. It could be described as amplitude (voltage), phase, frequency, position or any other measurable quality that can be compared against some other quantity.

But it's not digital until the quality represents something.

yeah, in a manner of thinking all an A/D converter is a machine for applying the agreed upon choice to the signal and then turning it into another signal where all information except the 0 and 1 is lost.

That's more like a simple schmitt trigger threshold. While the ADC does eliminate some data due to aliasing, ADC's will encode an analog value, from high to low according to it's bit depth: a 4-bit ADC might encode black as 0000 and white as 1111, with middle grey being 1010.

Imagine a simple ADC which is an array of threshold triggers that are set in evenly spaced intervals, and are in turn fed to binary encoder. When the first trigger voltage is reached, it's output to the encoder goes high, if the second threshold voltage is met, then it's output goes high, and so on until the maximum voltage condition is met. The encoder then converts the input into digital data which can be used elsewhere to say something about the analog input.

This is not really how a camera ADC works, but is rather a simple example of how analog data can be converted into digital data.

 

[Solarflare]

Well, for example, CCD react really nasty if the maximum voltage is reached and the pixel overloads. Thats why most CCDs not used for science or the military have overflow protection mechanisms in each pixel. These mechanisms already kick in before the pixel actually overloads, causing a somewhat different reaction to this situation than with CMOS fotosensors. This leads to an image somewhat more closer to what chemical film looks like.

Theres other things and I really only found very little sources to this kind of thing. All in all CCDs tend to create more "beautiful" colors. Thats one reason why Leica used CCDs, not CMOS, in their Leica M8 and M9 cameras, even if today CCDs are inferior to noise compared to CMOS.

Analog doesn't really exit !

Quantum physics rules !

Lol !

Not really, Plank's constant is so extremely small that effects like noise are much stronger and the fact that energy is split into parts is pretty much irrelevant in this respect.

 

[bhop]