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uk.tech.digital-tv (Digital TV - General) (uk.tech.digital-tv) Discussion of all matters technical in origin related to the reception of digital television transmissions, be they via satellite, terrestrial or cable. Advertising is forbidden, with no exceptions.

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  #31  
Old February 13th 17, 03:20 AM posted to uk.tech.digital-tv
Tim+[_4_]
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Davey wrote:
On Sun, 12 Feb 2017 22:39:00 -0000 (UTC)
Tim+ wrote:

Read my comment again. My point was that all good cameras have IR
filtering, only cheaper ones leave it out.


Not arguing, just curious. Why have IR filtering?


Can you see IR? Why would you want a camera that distorts what you see be
being sensitive to invisible parts of the EM spectrum?

Tim

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Please don't feed the trolls
  #32  
Old February 13th 17, 07:29 AM posted to uk.tech.digital-tv
Woody[_5_]
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"Tim+" wrote in message
news
Davey wrote:
On Sun, 12 Feb 2017 22:39:00 -0000 (UTC)
Tim+ wrote:

Read my comment again. My point was that all good cameras have IR
filtering, only cheaper ones leave it out.


Not arguing, just curious. Why have IR filtering?


Can you see IR? Why would you want a camera that distorts what you
see be
being sensitive to invisible parts of the EM spectrum?



Because sensors are wideband. They are also sensitive to UV but much
of that is stopped by the lens.

If manufacturers tried to produce a narrowband sensor that only
covered the visible spectrum it would affect the flatness of the
overall response. By making a sensor that is wider than required it
not only puts the visible spectrum into a 'flatter' area of the
response but it also makes them cheaper and more consistent to
manufacture.

Think back to hi-fi with audio responses way up into the tens of
kilohertz where humans can only hear up to around 20KHz or less?
Simple, again for flatness of response and in the case of harmonics
for the reality of the sound.


--
Woody

harrogate3 at ntlworld dot com


  #33  
Old February 13th 17, 08:53 AM posted to uk.tech.digital-tv
Tim+[_4_]
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Posts: 169
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Woody wrote:

"Tim+" wrote in message
news
Davey wrote:
On Sun, 12 Feb 2017 22:39:00 -0000 (UTC)
Tim+ wrote:

Read my comment again. My point was that all good cameras have IR
filtering, only cheaper ones leave it out.

Not arguing, just curious. Why have IR filtering?


Can you see IR? Why would you want a camera that distorts what you
see be
being sensitive to invisible parts of the EM spectrum?



Because sensors are wideband. They are also sensitive to UV but much
of that is stopped by the lens.

If manufacturers tried to produce a narrowband sensor that only
covered the visible spectrum it would affect the flatness of the
overall response. By making a sensor that is wider than required it
not only puts the visible spectrum into a 'flatter' area of the
response but it also makes them cheaper and more consistent to
manufacture.

Think back to hi-fi with audio responses way up into the tens of
kilohertz where humans can only hear up to around 20KHz or less?
Simple, again for flatness of response and in the case of harmonics
for the reality of the sound.



Then why do good digital cameras not see IR? If it were a genuine advantage
all digital cameras would reveal IR. Would phone manufacturers go to the
trouble of putting an IR filter on the "good" high res camera but not the
selfie one?

Tim

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  #34  
Old February 13th 17, 09:05 AM posted to uk.tech.digital-tv
Roderick Stewart[_3_]
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On Mon, 13 Feb 2017 04:20:27 -0000 (UTC), Tim+
wrote:

No because some good cameras have an IR filter.

Read my comment again. My point was that all good cameras have IR
filtering, only cheaper ones leave it out. If your mobile phone or digital
camera sees IR, it's because of penny pinching by the manufacturer.
Clearly the Galaxy S7 camera is not as good as it could be.


The absence of an IR filter on the S7 doesn't seem to have had any
adverse effect on the pictures it can take, and it can be used to
check remote controls *as well* as taking pictures. Therefore, it
could be argued that it is a *better* camera than one which does not
have this extra feature.


Um, more useful for checking remotes, not better for accurate colour
rendition.

Can you see IR with your naked eye? No. So why should a camera that
renders IR in the visible light spectrum when taking pictures take better
pictures? It's turning something invisible into a visible artefact in your
photos.


I agree with you that pictures from a camera that is sensitive to IR
as well as visible light *should* be expected give less realistic
pictures, as the colorimetry doesn't exactly match the human eye, but
the reality is that the pictures are subjectively very close to the
appearance of real scenes, at least in daylight. In artificial light,
which these days could be LED, CFL, mercury vapour, sodium vapour or
tungsten filament, there's no guarantee of consistency at all, but
most modern phone cameras make quite a good job of adjusting things
automatically to get a reasonably pleasing memento of the occasion,
which is usually all that is wanted.

Rod.
  #35  
Old February 13th 17, 09:09 AM posted to uk.tech.digital-tv
Roderick Stewart[_3_]
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On Mon, 13 Feb 2017 04:20:32 -0000 (UTC), Tim+
wrote:

Can you see IR? Why would you want a camera that distorts what you see be
being sensitive to invisible parts of the EM spectrum?


Perhaps it's difficult to make a filter that blocks IR without also
blocking too much visible red?

Rod.
  #36  
Old February 13th 17, 10:49 AM posted to uk.tech.digital-tv
Tim+[_4_]
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Posts: 169
Default Humax HDR - 2000T

Roderick Stewart wrote:
On Mon, 13 Feb 2017 04:20:32 -0000 (UTC), Tim+
wrote:

Can you see IR? Why would you want a camera that distorts what you see be
being sensitive to invisible parts of the EM spectrum?


Perhaps it's difficult to make a filter that blocks IR without also
blocking too much visible red?

Rod.


I somehow doubt that given than most digital cameras in my experience *do*
have IR filtration.

In practice I would agree that for phone cameras it probably makes little
difference (that most of us would notice). Manufacturers must be adding the
extra level of filtration for a reason though...

Tim

--
Please don't feed the trolls
  #37  
Old February 13th 17, 11:33 AM posted to uk.tech.digital-tv
Chris J Dixon
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Posts: 216
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Martin wrote:

The PVR button on the controller should light up each time the controller sends
a commend. If the battery is flat it won't.


I was just about to say the same. Sometimes the answer is simpler
than we make it. ;-)

Chris
--
Chris J Dixon Nottingham UK


Plant amazing Acers.
  #38  
Old February 15th 17, 08:21 PM posted to uk.tech.digital-tv
Vir Campestris
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Posts: 346
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On 13/02/2017 08:29, Woody wrote:
Because sensors are wideband. They are also sensitive to UV but much
of that is stopped by the lens.

If manufacturers tried to produce a narrowband sensor that only
covered the visible spectrum it would affect the flatness of the
overall response. By making a sensor that is wider than required it
not only puts the visible spectrum into a 'flatter' area of the
response but it also makes them cheaper and more consistent to
manufacture.

Think back to hi-fi with audio responses way up into the tens of
kilohertz where humans can only hear up to around 20KHz or less?
Simple, again for flatness of response and in the case of harmonics
for the reality of the sound.


I wouldn't mind the camera "seeing" IR if this meant that's how it was
in the displayed image. Just as I'd be unhappy with a stereo which not
only could reproduce bat squeaks, but shifted them down into the audible
range.

I know of devices that have electrically moveable IR filters so they can
automatically select either full colour or IR illumination as conditions
suggest.

Andy
 




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