Bayer sensor design

Bayer sensor

nev­er heard of it? By the way, the term has noth­ing to do with the chem­i­cal com­pa­ny of the same name. Here’s a brief expla­na­tion of what it’s all about:

Nor­mal­ly, the light-sen­si­tive pix­els of dig­i­tal cam­era sen­sors can­not dis­tin­guish col­ors; they only “see” bright­ness. There­fore, in order to dis­tin­guish col­ors, col­or fil­ters are placed in front of the indi­vid­ual light-sen­si­tive pho­to­cells of the sen­sor chip, which then only allow light of the rel­e­vant col­or to pass through. Cor­re­spond­ing to the three col­or-sen­si­tive cones of our reti­na, these col­or fil­ters are red, green and blue (RGB). Most sen­sors use a “Bay­er” arrange­ment in a 2x2 grid, which con­sists of one red, one blue and two green fil­ters. Green is used twice, since our eye is par­tic­u­lar­ly sen­si­tive in this area. 

Wikipedia writes about this:

A Bay­er fil­ter mosa­ic is a col­or fil­ter array (CFA) for arrang­ing RGB col­or fil­ters on a square grid of pho­to­sen­sors. Its par­tic­u­lar arrange­ment of col­or fil­ters is used in most sin­gle-chip dig­i­tal image sen­sors used in dig­i­tal cam­eras, cam­corders, and scan­ners to cre­ate a col­or image. The fil­ter pat­tern is half green, one quar­ter red and one quar­ter blue. It is named after its inven­tor, Bryce Bay­er of East­man Kodak. Bay­er is also known for his recur­sive­ly defined matrix used in ordered dither­ing.

The col­or fil­ter arrange­ment then looks like this:

From Amada44 - Eigenes Werk, Geme­in­frei,

There­fore, it becomes clear that the sen­sor res­o­lu­tion of the indi­vid­ual col­ors must always be low­er than the total res­o­lu­tion. The cam­eras or the RAW con­vert­ers cal­cu­late the col­or of each indi­vid­ual pix­el with more or less suit­able algo­rithms from the col­or dis­tri­b­u­tion of the adja­cent pix­els, which nev­er fits to 100%. Effec­tive­ly, there­fore, the col­or chan­nel green offers only half and the oth­er col­or chan­nels only a quar­ter of the spec­i­fied sen­sor res­o­lu­tion. This is usu­al­ly not a big prob­lem, because our eye does not han­dle this in a fun­da­men­tal­ly dif­fer­ent way. Our reti­na con­tains sig­nif­i­cant­ly few­er col­or-sen­si­tive cells (approx. 6 mil­lion so-called cones) than bright­ness-sen­si­tive cells (approx. 110 mil­lion so-called rods).

By the way, although the Bay­er design is by far the most com­mon sen­sor design, there are oth­er ways to teach col­or vision to col­or blind sensors.

Fuji­film, for exam­ple, uses a dif­fer­ent col­or matrix in its X-Trans sensors:

Dieses Bild hat ein leeres Alt-Attribut. Der Dateiname ist XTrans_matrix.png

Sig­ma has also devel­oped the so-called Foveon sen­sor, in which the col­or fil­ters are arranged one behind the oth­er to ensure a fin­er col­or resolution.

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