SLR camera definition

[Elie]

Wow thanks guys!
Understood loud and clear!

Maybe I should start a new thread ont he differences between Foveon and CCD LOL

Thanks again!

Cheers,
Elie

[az]

Simple

The photodiodes on a CCD sensor cannot see colour, they only see light intensity.

On a traditional ("Bayer") CCD sensor youone photodiode per pixel, and an array of colour filters in front of the sensor, one colour for each photodiode (green, red, green, and blue - yes, 2x green, because the human eye is more sensitive to green than to other colours). So each photodiode can only see one colour. Colour gets interpolated, which is no big problem, because (as you probably already know from video) the human eye is more sensitive to luminance (brightness) than to chrominance (colour). This only introduces problems for certain patterns, resulting in moiré or reduced resolution.

The Foveon X3 sensor has THREE photodiodes per pixel, behind each other. This works because certain frequencies of light penetrate silicon a little deeper than others, reaching the second or third sensor. The 3 megapixel X3 sensor actually has 9 million photodiodes (3mp times three).

AZ

[Marshmallowman]

CCD = "charge coupled device"...not really a diode

[az]

I don't know why, but they are called photodiode (at least on dpreview, and I think I've seen it somewhere else also).

AZ

[VJ]

Yup, the individual pixels are called photodiodes.

Most cameras use GRGB (green, red, green, blue) as az stated, some cameras use CMY (cyan, magenta, yellow), and now Sony is using a different layout: RGBE (red, green, blue, emerald)

http://www.dpreview.com/news/0307/03071601sonyrgbeccd.asp

This is the sensor in the F828.

The Foveon has the disadvantage that - while some frequencies penetrate deeper in the silicon - the colour positioned the lowest does get less light.

http://www.foveon.com/X3_tech.html

This leads to more noise in green and red (most in red), than is present in blue.

It is clear that this has opened a discussion: the Foveon reads 1 pixel at one position, whereas the traditional bayer sensors need to apply specific interpolation between a pixel (=1 colour) and it neighboring pixels (=another colour). Suppose Foveon have a sensor with 1 million pixels: it reads 3 x 1 million photodiodes; a bayer sensor that would do this has 3 million photodiodes.

The discussion then concerns:
Which is the sharpest ? (bayer: sensors are spread over an area, this benefits the sharpness, but the interpolation has a negative effect on it)
Can Foveon state they have a 3 megapixel sensor ?
(no: only 1 million individual positions / yes: 3 million photodiodes)
Can the bayer sensor state they have 3 megapixels ?
(no: the 3 million pixels are not independant / yes: 3 million photodiodes)


Jörg

[Marshmallowman]

Indeed it is my mistake

I keep thinking of things they used to be (non silicon)