Re: Bayer sensor and MX


"Sosumi" <sosumi@xxxxxxx> schreef in bericht news:wNadnSk0HdDS-THanZ2dneKdnZydnZ2d@xxxxxxxxxxx
The way the Bayer sensor works, it "makes up" color information depending on the surrounding pixels. But if you do multiple exposures with exactly the same scene, the picture gets more sharp according to the amount of exposures.

No the picture does not get more sharp. If there is a lot of noise in one normal
picture, the definition of the picture get's a littlebit better, but for most normal
pictures (in normal light) taking more pictures of the same scene does not make
it sharper.

In theory small movements of the camera and adjusting for these movements
when adding the pictures, will give a better picture and less risc of moire.
In theory this method can even make pictures sharper, but then you need
a very large amount of the 'same' pictures to get the pictures noticeble sharper.


Much is due to the fact that noise is distributed randomly and hence, the same place where a "piece" of noise was before, it's over written with data the next exposure.
Multiple pictures will reduce the noice, but with correctly exposed pictures
there is not a lot of noise. (Long exposure pictures will benefit from multiple
exposure, but not normally exposed pictures).




What I was wondering: do the pixel interpolation always work the same way? Or is this also slightly random (shifting)? So do you, in fact, get more information or only less noise? It just seems hard to believe, that every take of a picture would give exactly (I mean pixel deep peeping) the same result.

And also: do all Bayer sensor work exactly the same, or is there a difference in Nikon, Canon, older, newer models?

There are some variations.
Most sensors have 2 greens, 1 red and 1 blue for every four cells in a square.
There are sensors where the second green is replace by another color.
There are sensors which are not RGB, but YMC, but I haven's seen them them lately
in camera's.

Normal Bayer sensors

GRGRGRGR
BGBGBGBG
GRGRGRGR
BGBGBGBG

Interpolation which is most simple is that, on each pixel

Green pixel (position).
Green = G (from the pixel)
Red= (Rl+Rr)/2 from the left and the right
Bleu = (Bu+Bd)/2 from the up and down bleu.

Red pixel (position).
Green = (Gl+Gr+Gu+Gd)/4
Red = R (from the pixel)
Bleu = (B+B+B+B)/4 from the 4 corners of R

Bleu pixel (position).
Green = (Gl+Gr+Gu+Gd)/4
Red = (R+R+R+R) /4 from the 4 corners of B
Bleu = B (from the pixel)

This is without sharpening or any other fancy stuf.
(In general sharpening subtracts a little bit of pixels laying further away).

When using multiple exposure with shifted pixels, something similar is done,
with far smaller pixels, where the 'large' pixels are shifted over the small pixels.
Using sharpening this will result in a slightly sharper picture.

As you can see the Red and Bleu pixels (positions) get the information of the
Bleu and Red colors from quite some distance.
The resolution for red only or bleu only is significant less than for black and white.

ben





--
Sosumi


.

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