Bayer mosaic filter array question

The figures in most documentation, that depicts the Bayer filter array,
show the green filter elements as green, the red as red and the blue as
blue. Is that true in reality? Are the green ones really green? For
the purposes of this question let's say they it's true.

The role of the individual elements of the Bayer pattern is to filter
(turn to heat?) their associated color - e.g. the green elements turn
green light to heat and pass red and blue. Is that correct?

The upshot of the GRGB Bayer mosaic is the transmission (pass to the
sensor) of a third more blue/red light than green. Is that correct?

Thanks,
Ron

The figures in most documentation, that depicts the Bayer filter array,
show the green filter elements as green, the red as red and the blue as
blue. Is that true in reality? Are the green ones really green? For
the purposes of this question let's say they it's true.

It is.

The role of the individual elements of the Bayer pattern is to filter
(turn to heat?) their associated color - e.g. the green elements turn
green light to heat and pass red and blue. Is that correct?

No, a green element would pass green light to the sensor, and convert
other wavelengths to heat.

The upshot of the GRGB Bayer mosaic is the transmission (pass to the
sensor) of a third more blue/red light than green. Is that correct?

Yes. That's because the human eye is much more sensitive to green than to
red or blue, so by doubling up the green sensors, the data recorded is
somewhat closer to what our brains expect.

steve

writes:


The figures in most documentation, that depicts the Bayer filter array,
show the green filter elements as green, the red as red and the blue as
blue. Is that true in reality? Are the green ones really green?

Yes.

The role of the individual elements of the Bayer pattern is to filter
(turn to heat?) their associated color - e.g. the green elements turn
green light to heat and pass red and blue. Is that correct?

No, it's the other way around: green elements pass green light and
turn red and blue to heat.

The upshot of the GRGB Bayer mosaic is the transmission (pass to the
sensor) of a third more blue/red light than green. Is that correct?

No. The Bayer pattern transmits mostly green. Green is half the
overall light transmitted, and twice the level of blue or red. The
reason for this is that the human eye is much more sensitive to green
light than it is to red or blue light. The Bayer pattern simply
profits from this idiosyncrasy, improving resolution in green at the
expense of resolution in blue and red.

Some sensors have used secondary primaries (cyan, yellow, and magenta)
to increase sensitivity to light. This increases low-light
performance and luminance resolution at the expense of color accuracy
and resolution.

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Yes. That's because the human eye is much more sensitive to green than to
red or blue, so by doubling up the green sensors, the data recorded is
somewhat closer to what our brains expect.

steve

Hi Steve,

What is still throwing me off is, why would the Bayer filter pass more
green if that is what humans are most sensitive to? Doesn't it make
more sense to pass the light we are less sensitive to and transmit more
of the parts of the visible spectrum we are less sensitive to? It
seems like to pass more of the light we are most sensitive to would be
to compound an imbalance.

Thanks,
Ron

reason for this is that the human eye is much more sensitive to green
light than it is to red or blue light. The Bayer pattern simply
profits from this idiosyncrasy, improving resolution in green at the
expense of resolution in blue and red.


Hi,

You mention that green is used because it gives better resolution but
wouldn't blue be better at improving resolution since it has a
shorter wavelength? Is it because blue would require longer exposures?

Thanks for the reply,
Ron

wrote:
The figures in most documentation, that depicts the Bayer filter array,
show the green filter elements as green, the red as red and the blue as
blue. Is that true in reality? Are the green ones really green? For
the purposes of this question let's say they it's true.

The role of the individual elements of the Bayer pattern is to filter
(turn to heat?) their associated color - e.g. the green elements turn
green light to heat and pass red and blue. Is that correct?

The upshot of the GRGB Bayer mosaic is the transmission (pass to the
sensor) of a third more blue/red light than green. Is that correct?

Thanks,
Ron

Depends on the type of filter. Some filters reflect the light that the
filter does not transmit, others absorb it. My impression is the ones
used in the mosaic is the type that reflects the unwanted light. There
is a terminology issue here- I would call the green filter the one that
TRANSMITS the green. Same with the other two. A filter of the
intererence/reflecting type appears purple in appearance if you view it
from the front, green if you view it from the back.

Depends on the type of filter. Some filters reflect the light that the
filter does not transmit, others absorb it. My impression is the ones
used in the mosaic is the type that reflects the unwanted light. There
is a terminology issue here- I would call the green filter the one that
TRANSMITS the green. Same with the other two. A filter of the
intererence/reflecting type appears purple in appearance if you view it
from the front, green if you view it from the back.

Leave it to me to complicate and confuse something that should be so
easy. I think that when I see diagrams like figure three at this link:
http://www.microscopyu.com/articles/...orbalance.html
When I see the arrow and the reference to the green filter I will think
to myself, green 'pass' filter. Like the 'ew' in New Orleans, you
never say the 'ew' just say N'orleans and think 'ew'.

Thanks,
Ron

writes:

What is still throwing me off is, why would the Bayer filter pass more
green if that is what humans are most sensitive to?

Because you need high resolution in the green, and that in turn is
because human beings can resolve detail best in that color. A lack of
resolution in green is much more obvious than a lack of resolution in
blue or red.

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writes:

You mention that green is used because it gives better resolution but
wouldn't blue be better at improving resolution since it has a
shorter wavelength?

The wavelengths of these different frequencies of light are far
smaller than the retinal structures that capture them, so the shorter
wavelength of blue light doesn't have any real effect on the resolving
power of the eye, which is very coarse by comparison with wavelengths.

Red light has a wavelength of about 564 nm, whereas the spacing
between cone cells is around 8000 nm, or about 14 times the wavelength
of red (and 19 times the wavelength of blue).

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writes:

Depends on the type of filter. Some filters reflect the light that the
filter does not transmit, others absorb it. My impression is the ones
used in the mosaic is the type that reflects the unwanted light.

I think not. That would cause unwanted artifacts.

Dichroic filters (the kind that reflect the unwanted light) are used
in the prisms of 3-CCD video cameras, so that no light is wasted. But
that wouldn't help in a mosaic filter placed directly over the CCD.

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