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What is the definition of pixel?
Excuse me if this question was asked before..

I always wonder what is the definition of CCD pixel. Most of digital cameras use bayer mask CCD, which 2 green dots, 1 red dot and 1 blue dot constitute 1 RGB dot. Does it mean a 12M pixels CCD actually has only 3M RGB pixels?..

Comments (5)

One pixel per detector. Each detector influences the value of multiple pixels, not just one so it's not a 'three detector == one pixel' relationship...

Comment #1

Lyblly wrote:.

I always wonder what is the definition of CCD pixel..

Or in the more expensive cameras, CMOS rather than CCD.

Most of digitalcameras use bayer mask CCD, which 2 green dots, 1 red dot and 1 bluedot constitute 1 RGB dot. Does it mean a 12M pixels CCD actually hasonly 3M RGB pixels?.

No, the pixels for the final image are formed by analyzing the each one color pixel on the sensor and the pixels surrounding it. The final image pixel is basically the result of a interpolation of a group of pixels. The process is called demosaicing (sometimes spelled with a k)..

There are lots of different algorithms for this. Some just look at nearest neighbors, others look further a field but give more weight to the nearest neighbor pixels. Green photosites are generally better at detecting light sensitivity, and more weight is given to them in terms of luminosity. The red and blue photosites are given more emphasis in chroma (color) determination..

Brian A...

Comment #2

Hugowolf wrote:.

Lyblly wrote:.

I always wonder what is the definition of CCD pixel..

Or in the more expensive cameras, CMOS rather than CCD.

Digressing a little from the original topic here, it's true that some cameras use CMOS instead of CCD. These cameras may be expensive, or they may be cheap.In some cases it's the inexpensive ones that use CMOS, for examplehttp://www.dpreview.com/news/0707/07072501kodakc513.aspAlso many inexpensive webcams use CMOS instead of CCD..

The well-known exception to this is the successful use of high-quality CMOS in many DSLR cameras.Regards,Peter..

Comment #3

Lyblly wrote:.

Excuse me if this question was asked before..

You are excused. It HAS been discussed a lot. And it's a confusing topic for many people..

I always wonder what is the definition of CCD pixel..

Drop the "CCD" part. A "pixel" is a "picture element". A "pixel" can't be divided any further...it's the smallest thing that can be used to make a digital "picture". A "picture" is a group of multi-colored dots, so each of those multi-colored dots is a pixel..

On the monitor in front of you, a "pixel" is different than in a camera. Monitors don't have "multi-colored" dots...each dot is ONE color...RGB. It takes 3 of the dots on your monitor to make one "pixel". To display a picture on your monitor, each "pixel" in the picture has to be split into 3 colors...RGB. This is the OPPOSITE of what goes on in your camera..

Each sensitive spot on a Bayer sensor is called a "photosite", which is just shorthand for "photosensitive site". Each "photosite" has an associated color filter. Dr. Bayer specified a 4-photosite matrix, with RGBG color filters. Each of these "photosites" is NOT a "pixel"...in fact a Bayer sensor doesn't have ANY "pixels"...only "photosites"! The pixels are created later in the computer that demosaics the Bayer data. Each photosite will BECOME a pixel later and there are almost as many "pixels" as "photosites" in the resulting image..

Almost? Yes! Did you ever notice that Phil and most other camera review sites quote both "Total Pixels" and "Effective Pixels" in the camera specifications? What is this about? As has already been stated, the "pixels" are created by analyzing MANY "photosites" surrounding one "photosite" to determine the correct color. At the EDGE of a sensor, how does the demosaicing algorithm do this? To solve this dillema, sensor manufacturers add some "extra" photosites around the edge. Using these "extra" photosites, the demosaicing algorithm can get started and by the time it gets to the "Effective" photosites, everything is working. The "extra" "pixels" are thrown away...well, in some instances they are still there and some of them can actually be retrieved!.

Most of digitalcameras use bayer mask CCD, which 2 green dots, 1 red dot and 1 bluedot constitute 1 RGB dot. Does it mean a 12M pixels CCD actually hasonly 3M RGB pixels?.

No, as I explained above, each of the 12M "photosites" will become a "pixel" after Bayer demosaicing had been done..

Most people have to sleep on this concept for a while before understanding the magic Dr. Bayer did....

Sensors have photosites...Cameras have pixels....

Charlie DavisNikon 5700 & Sony R1HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #4

Excellent answer. Also thanks other who answered my question...

Comment #5

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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