[Elphel-support] Extension of stereobase and elongation sensor's cable length

[support-list]

Hello Anatoly,

> I am not familiar with sensor's details but I know that in color sensor actual resolution for every color channel  is lower than resolution provided in specification.
> For example if we consider color sensor 200 x 200 px then actual resolution for Red and Blue channel is 100 x 100 because of Bayer filter. Final image resolution 200 x 200 is obtained by interpolation.

That is not always true. Pixel size is still the same, and if you are measuring distance to a large object (that includes many pixels), you can still measure x and y coordinates to a sub-pixel resolution, and then use it to calculate disparity, and so Z. On the other hand modern sensors have higher resolution, than lenses and chromatic aberration reduces overall resolution significantly. Processing each color channel separately provides you with better resolution than using a monochrome sensors where you have no way to separate chromatic aberration from other types.

>My another knowledge is that monochrome sensor has a much higher sensitivity than color one at the same resolution. That is why I guess that using the monochrome sensor let me obtain higher ratio of signal/noise at the same resolution than color sensor.

No, it may sound counter-intuitive, but the modern color sensors actually have better sensitivity than monochrome ones. It is because of the microlenses that focus light on photo-sensitive parts of the pixel.

>At the same time at the half (about 1MP) resolution we obtain much more contrast contour. 

Actually both color and monochrome Aptina sensors (same applies to other ones too) are not optimal for using with decimation and binning - that mode is a "viewfinder" or "preview" mode. Even monochrome sensors have the same array organization as the color ones (the sesnors is designed to be color), so when you decimate in half in both directions, instead of:
RGRGRGRGRG
GBGBGBGBGB
RGRGRGRGRG
GBGBGBGBGB
RGRGRGRGRG
GBGBGBGBGB
RGRGRGRGRG
GBGBGBGBGB

you get:

RG..RG..RG
GB..GB..GB
........
........
RG..RG..RG
GB..GB..GB

For monochrome You may just replace all color letters with "M':

MM..MM..MM
MM..MM..MM
........
........
MM..MM..MM
MM..MM..MM

Andrey








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