So, for a 3x3 image, the input data would be 9 values like:

   R G B
   B R G
   G B R

?

If you want "3x3 colored image", you would need 6x6 of the bayer filter pixels.

Each RGB pixel would be 2x2 grid of

``` G R B G ```

So G appears twice as many as other colors (this is mostly the same for both the screen and sensor technology).

There are different ways to do the color filter layouts for screens and sensors (Fuji X-Trans have different layout, for example).

This depends on the camera and the sensor's bayer filter [0]. For example the quad bayer uses a 4x4 like:

    G G R R
    G G R R
    B B G G
    B B G G

[0]: https://en.wikipedia.org/wiki/Bayer_filter

In the example ("let's color each pixel ...") the layout is:

  R G
  G B

Then at a later stage the image is green because "There are twice as many green pixels in the filter matrix".

And this is important because our perception is more sensitive to luminance changes than color, and with our eyes being most sensitive to green, luminance is also. So, higher perceived spatial resolution by using more green [1]. This is also why JPG has lower resolution red and green channels, and why modern OLED usually use a pentile display, with only green being at full resolutio [2].

[1] https://en.wikipedia.org/wiki/Bayer_filter#Explanation

[2] https://en.wikipedia.org/wiki/PenTile_matrix_family

Funny that subpixels and camera sensors aren't using the same layouts.

Pentile displays are acceptable for photos and videos, but look really horrible displaying text and fine detail --- which looks almost like what you'd see on an old triad-shadow-mask colour CRT.