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Old Sep 3, 2006, 3:00 PM   #1
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My basic understanding is that noise is generated when amplifying weak signals from each pixel. The smaller the pixel the weaker the original signal. I know in sound amplification more than one level of amplification is used. With turntables there was a third level, pre-pre-amp. The pre-amp was designed to boost a weak signal to level for normal amplification, with very low distortion.

Do digital cameras use more than one level of amplification? If not could they benefit from more than one stage of amplification?
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Old Sep 4, 2006, 2:08 AM   #2
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This is a digital system so there is no amplification of the signal as such as you referred to in analogue audio systems.


The voltage levels from the sensor array is processed by an analogue to digital converter that represents the picture as a series of numbers.

These numbers can be accurately handled through all the storage and procesing functions until they are output in an analogue form to monmitor or printer for viewing.

The purpose of amplification in the audio system is to generage an output voltage large enough to operate an electro-mechanical device, ie move the cones of the loudspeakers.

But any noise pesent at the start will be amplified and if loud enough will be heard. Typically it could be from tape hiss, turntable rumble, or quantising noise from CD players.

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Old Sep 4, 2006, 4:54 AM   #3
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All that aside, there's absolutely nothing than we, as the mere end user, can do - the noise level will be what ever it is, at whatever ISO setting is used.

The only choice we have is to choose a camera with the lowest noise output - I believe that the Pentax falls into this category when using higher ISOs.
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Old Sep 4, 2006, 10:35 AM   #4
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You have to start with an anolog original before converting to digital. Digital sound recording strts with an analog signal from a microphone. Is there a DA converter in the camera?
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Old Sep 4, 2006, 3:06 PM   #5
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[align=left]A CMOS image sensor
Instead of film, a digital camera has a sensor that converts light into electrical charges.
The image sensor employed by most digital cameras is a charge coupled device (CCD). Some cameras use complementary metal oxide semiconductor (CMOS) technology instead. Both CCD and CMOS image sensors convert light into electrons. A simplified way to think about these sensors is to think of a 2-D array of thousands or millions of tiny solar cells.
Once the sensor converts the light into electrons, it reads the value (accumulated charge) of each cell in the image. This is where the differences between the two main sensor types kick in: [/align]

[align=left]
  • A CCD transports the charge across the chip and reads it at one corner of the array. An analog-to-digital converter (ADC) then turns each pixel's value into a digital value by measuring the amount of charge at each photosite and converting that measurement to binary form.
[/align][/*]
  • CMOS devices use several transistors at each pixel to amplify and move the charge using more traditional wires. The CMOS signal is digital, so it needs no ADC. [/*]
    [align=left][/align]
[align=left]

Photons hitting a photosite and releasing electrons
Differences between the two types of sensors lead to a number of pros and cons:



A CCD sensor
[/align]
[*]
[/*]
  • CCD sensors create high-quality, low-noise images. CMOS sensors are generally more susceptible to noise. [/*]
  • Because each pixel on a CMOS sensor has several transistors located next to it, the light sensitivity of a CMOS chip is lower. Many of the photons hit the transistors instead of the photodiode. [/*]
  • CMOS sensors traditionally consume little power. CCDs, on the other hand, use a process that consumes lots of power. CCDs consume as much as 100 times more power than an equivalent CMOS sensor. [/*]
  • CCD sensors have been mass produced for a longer period of time, so they are more mature. They tend to have higher quality pixels, and more of them.
Although numerous differences exist between the two sensors, they both play the same role in the camera -- they turn light into electricity. For the purpose of understanding how a digital camera works, you can think of them as nearly identical devices. Resolution
The amount of detail that the camera can capture is called the resolution, and it is measured in pixels. The more pixels a camera has, the more detail it can capture and the larger pictures can be without becoming blurry or "grainy."
Some typical resolutions include: [/*]
  • 256x256 - Found on very cheap cameras, this resolution is so low that the picture quality is almost always unacceptable. This is 65,000 total pixels. [/*]
  • 640x480 - This is the low end on most "real" cameras. This resolution is ideal for e-mailing pictures or posting pictures on a Web site. [/*]
  • 1216x912 - This is a "megapixel" image size -- 1,109,000 total pixels -- good for printing pictures. [/*]
  • 1600x1200 - With almost 2 million total pixels, this is "high resolution." You can print a 4x5 inch print taken at this resolution with the same quality that you would get from a photo lab. [/*]
  • 2240x1680 - Found on 4 megapixel cameras -- the current standard -- this allows even larger printed photos, with good quality for prints up to 16x20 inches. [/*]
  • 4064x2704 - A top-of-the-line digital camera with 11.1 megapixels takes pictures at this resolution. At this setting, you can create 13.5x9 inch prints with no loss of picture quality.
[/*]
[align=center]


The size of an image taken at different resolutions
[/align]
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Old Sep 4, 2006, 4:11 PM   #6
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So the Pentax does have a DA converter since it uses a CCD chip. Some form of amplification must be needed to boost weak signals. It may be incorporated in the sensor chip and require a new sensor design to change.
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Old Sep 5, 2006, 3:18 PM   #7
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snooked wrote:
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So the Pentax does have a DA converter since it uses a CCD chip. Some form of amplification must be needed to boost weak signals. It may be incorporated in the sensor chip and require a new sensor design to change.

No. CCD is a pure analog chip. Basically, each row of cellsare chained together. When signaled, each CCD cell dumps its charge to the next one. So you only need one ADC at the end of the chain/row to read the charges one by one. The noise comes from the CCD cell itself. The only way to make it less is either make the cell larger or maybe cool it down. That's why on the same size CCD, higher pixel count usually means higher noise. On the other hand, for the same pixel count, larger CCD means less noise. That's why APS sized CCD used in Pentax and other DSLRs are less noisy than consumer digicams. A full frame CCD used in more expensive semi-pro DSLRs are even better than the APS sized CCD we have.
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Old Sep 5, 2006, 7:34 PM   #8
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Is the noise generated by the sensor limited to a certain frequency range? For tape hiss, dolby boosts that area on recording and reduces it by the same amount on playback, alowing a higher overall dynamic range. Could a similar two step process work for the signal from a ccd sensor?
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Old Sep 5, 2006, 8:37 PM   #9
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Catbells wrote:
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All that aside, there's absolutely nothing than we, as the mere end user, can do - the noise level will be what ever it is, at whatever ISO setting is used.
no kidding!! think i'll go out and alter my ds right now for lower noise.. what's this thread about?? i'm sure pentax has a lot better electrical engineers than any of us here. there is absolutely nothing any of us can do about it. this thread reminds me of the endless gripes by RH... i tend to just ignore them and go on.. why worry about something you have no control over. well said catbells........
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Old Sep 5, 2006, 9:14 PM   #10
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i find this rather fascinating

maybe i cant do much about it, but the information may come in useful down the track

i did notice Ca...ns new Reb... only goes upto 1600ASA i guess that is to do wth the cmos chip
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