Bayer mosaic filter array question

ronviers DeleteThis @gmail.com 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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 >> Stay informed about: Bayer mosaic filter array question 

>
> 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
 >> Stay informed about: Bayer mosaic filter array question 

> 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
 >> Stay informed about: Bayer mosaic filter array question 

ronviers.TakeThisOut@gmail.com 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.
 >> Stay informed about: Bayer mosaic filter array question 

> 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/digitalimaging/colorbalance.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
 >> Stay informed about: Bayer mosaic filter array question 

> 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).
>
Finally I get it! Thanks for sticking with me.

Ron
 >> Stay informed about: Bayer mosaic filter array question 

ronviers RemoveThis @gmail.com 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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ronviers.RemoveThis@gmail.com 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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 >> Stay informed about: Bayer mosaic filter array question 

stauffer.RemoveThis@usfamily.net 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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<ronviers RemoveThis @gmail.com> wrote in message
news:1156478683.370474.80950@74g2000cwt.googlegroups.com...
>
> 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.
There are very tiny filters in front of the sensors which pass the displayed
color. The sensors have no color. It is just the filters that are colored.
>
> 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
>
> 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
>
> Thanks,
> Ron
>
Jim
 >> Stay informed about: Bayer mosaic filter array question 

"Jim" <jim-norris DeleteThis @sbcglobal.net> wrote in message
news:ipJHg.12898$kO3.10539@newssvr12.news.prodigy.com...
>
> <ronviers DeleteThis @gmail.com> wrote in message
> news:1156478683.370474.80950@74g2000cwt.googlegroups.com...
>>
>> 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.
> There are very tiny filters in front of the sensors which pass the
> displayed color. The sensors have no color. It is just the filters that
> are colored.
>>
>> 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
>>
>> 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
>>
>> Thanks,
>> Ron
>>
> Jim
>
The reason that these sensors are shown in a particular color is that that
is the color which they measure. Thus, there are twice as many green
sensitive sensors as either red or blue for the reason that another poster
stated.
Jim
 >> Stay informed about: Bayer mosaic filter array question 

Mxsmanic wrote:
> stauffer RemoveThis @usfamily.net 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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There are several kinds of "interference" filters- ones that use
physical optics. There are high pass and low pass ones, many of which
can be used as dichroics. There is also the bandpass. I believe the
filters on most mosaics are bandpass interference filters. I am not
sure which artifacts you mean. Yes, the reflected energy can cause
ghosts and flares if internal baffling is not good. But absorption
filters also reflect light, so baffling must be good in either case.
 >> Stay informed about: Bayer mosaic filter array question 

stauffer.RemoveThis@usfamily.net wrote:
> Mxsmanic wrote:
>
>>stauffer@usfamily.net 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.
>>
>>--
>>Transpose mxsmanic and gmail to reach me by e-mail.
>
>
> There are several kinds of "interference" filters- ones that use
> physical optics. There are high pass and low pass ones, many of which
> can be used as dichroics. There is also the bandpass. I believe the
> filters on most mosaics are bandpass interference filters. I am not
> sure which artifacts you mean. Yes, the reflected energy can cause
> ghosts and flares if internal baffling is not good. But absorption
> filters also reflect light, so baffling must be good in either case.
>
I don't think they are interference filters. The bandpass profiles
look more like simple absorption filters. Also, interference filters
also include absorption filters to block higher orders. Interference
filters are typically used in narrower bandpass applications than
RGB color.

Roger
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