«

"Kennedy McEwen" <> wrote in message
news:0wDy+...
> In article <i1sd2s$ajn$>, David J Taylor
> <david-> writes
>>
>>I was trying to keep it simple!
> Trying being the operative word.

To avoid exactly this level of detail.

>>Note that I said "might require a cooled detector", not "will".
> But you said "requires...10um", it doesn't and if you choose to work at
> 10um it certainly doesn't require a cooled detector.
>
>>All space-based instruments which I know about use cooled detectors, for
>>looking at earth-like (i.e. mug-like) temperatures, and the NET is
>>typically lower in a 10um detector than in a 3-5um one.
>>
> I assume that is because they are "looking" at each spot for a limited
> time, rather than operating to full performance without time
> limitations. Modern cooled infrared detectors are more like the sensors
> in digital cameras, matrix arrays. In these devices the exposure time
> is limited by the well capacity (just as the exposure of digital camera
> sensors to avoid saturation is limited by the pixel storage capacity).
> When you are storage capacity limited, instead of time limited, as with
> modern high performance cooled sensors, the NET of 3-5um detectors is
> around half that of an equivalent 10um device. For example, two
> otherwise identical devices, well into BLIP performance:
> http://tiny.cc/wnyeb is a 3-5um device with NETD of ~17mK while
> http://tiny.cc/f0032 is its 10um counterpart with NETD of ~32mK.
>
> Or, in exactly the same device which is sensitive in spectral regions:
> http://tiny.cc/ni4dw when operating dedicated to each band the 3-5um
> NETD is ~11mK, whilst the 8-10um NETD is ~22mK.
> --
> Kennedy

Yes, I'm talking scanned rather than staring arrays.

Thanks for the further info.

Cheers,
David

"David J Taylor" <david-> wrote in message
news:i1rugq$sum$...
> "DanP" <> wrote in message
> news:46365b3d-a169-4fa0-8995-...
> []
>> The information from an IR image has nothing to do with the colour.
>> A hot green mug will look different in IR than a plant with the same
>> shade of green.
>> So you cannot map IR to visible colour.
>>
>> DanP
>
> Be careful not to confuse near-IR with far-IR. With digital cameras and
> film it's the region just beyond the red end of the visible spectrum which
> people call "IR" - a wavelength of ~0.8um. Here, the prime difference is
> that the reflectance of vegetation is much higher and hence the
> characteristic appearance of monochrome IR images.
>


Almost!
Chlorophyll is transparent to waves in the near IR spectrum. Hence it
appears to be white. Similarly many clothing dyes are transparent in that
spectrum and also appear white. Particles in the air cause the sky to appear
blue. In this spectrum these particles do not reflect the energy waves and
thus appear black.

BTW I have submitted an IR photo in the SI.




--
Peter

"David J Taylor" <david-> wrote in message
news:i1t1et$fp4$...
[]
> Yes, I'm talking scanned rather than staring arrays.

... and with resolutions today of 3712 x 3712 pixels, and in a few years
time of nearer 11,000 pixels square. Mechanically scanned, with mirror
optics, covering 0.6um to 13um with a set of detectors.

Cheers,
David

"Peter" <> wrote in message
news:4c424ec1$1$5550$...
[]
> Almost!
> Chlorophyll is transparent to waves in the near IR spectrum. Hence it
> appears to be white. Similarly many clothing dyes are transparent in
> that spectrum and also appear white. Particles in the air cause the sky
> to appear blue. In this spectrum these particles do not reflect the
> energy waves and thus appear black.
[]

If anyone would like to know a little more, there's a training module
here, entitled:
"Monitoring Vegetation From Space".

http://www.satreponline.org/landsaf/index.htm

This section may be of particular interest:

http://www.satreponline.org/landsaf/...php?page=3.0.0

Cheers,
David

On Thu, 15 Jul 2010 20:09:04 -0500, Better Info <>
wrote:

>On Thu, 15 Jul 2010 20:48:55 -0400, Scotius <> wrote:
>
>> I know that color infra-red images look really weird (for lack
>>of a better term), but I once read that infra-red light cuts through
>>fog/haze etc better than regular light, which I suppose is why B & W
>>infra-red shots always look better than B & W shots without IR flash.
>> So I'm wondering if there's a program that could accurately
>>predict based on IR color what the colors present should be, and
>>convert them, so it would be possible to do color shots better in
>>haze, etc.
>> Anyone know of anything like this?
>
>Unless you know the precise IR spectral response of every material in
>nature or man-made, and were certain those exact same materials appeared in
>your scene, it would be impossible to convert the IR frequencies to known
>colors in the visible spectrum. Take for a simple example two green paints.
>One highly reflective of IR, the other highly absorbing of IR. If you shot
>an IR image of a green-painted object through the obscuring haze from a
>fire what color would you try to redefine it as?

I never thought of it that way. Well, thanks for making me
think... too much actually.
The reason I was asking is that when I recently covered a
concert for a local magazine, I spoke to one of the stage managers,
and he told me it would be okay to take a few shots with flash, but
not too many.
I thought that maybe with infra-red (invisible to the naked
eye), it would be great to be able to take a fully illuminated shot,
then go home and process it on the computer.
I suppose it would work fine it you were shooting B & W
infra-red, just not color, which is what I was most interested in.

>
>IR works great for shooting through the haze of immense forest-fires. I
>have quite a few majestic scenes and large panoramas of forest-fires in
>front of towering mountains and glacier-capped peaks, abnormally hidden
>from view by the dense forest-fire smoke but clearly revealed in IR. Unless
>I had similar images taken from the same locations at the same time of day
>during the same season of the year without the smoke present, I would be in
>error trying to convert the IR-luminosity spectral response of those hidden
>portions of those images to their full-color counterparts.

Well, you've convinced me. I still think B & W infra-red is a
good idea for not bothering a band or crew though... or am I wrong
about that too? Oh God don't let me be wrong about that too... can an
IR flash be seen (I'm hoping not)?

On Sat, 17 Jul 2010 13:42:15 +0100, Grimly Curmudgeon
<> wrote:

>We were somewhere around Barstow, on the edge of the desert, when the
>drugs began to take hold. I remember saying
>something like:
>
>>It would be something like trying to make a Big Mac taste like
>>cheese cake with cherry topping with out having cheese or cherries or
>>even knowing that what you have to start with is a Big Mac.
>
>Living by chemistry.
>I'm sure some food researchers are working on it.

Alexander Shulgin would probably be interested in it if he was
still alive... and then I'd be immediately NOT interested in it. I
just can't respect acid-loving hippies.

On Sat, 17 Jul 2010 13:46:37 +0100, Grimly Curmudgeon
<> wrote:

>We were somewhere around Barstow, on the edge of the desert, when the
>drugs began to take hold. I remember Kennedy McEwen
><> saying something like:
>
>>I was once asked by a senior member of the UK
>>Royal Family why the false colour pictures from a thermal camera,
>>representing temperature from blue being cold to red being hot, made
>>someone's shirt look orange when it was obviously blue. Just as I
>>repeated that it was false colour, a colleague jumped in and told him
>>not to worry because I would have that fixed in a day or two. No such
>>thing as a stupid question, just stupid people.
>
>Your colleague saw the Royal's eyes glaze over two sentences into the
>explanation and leapt in to save you. The Royals are notoriously
>difficult to penetrate with any meaningful knowledge, their inbreeding
>prevents it.

It's probably not so much that as it is them being distracted
by worrying if anyone's noticed their club feet.

On Sat, 17 Jul 2010 20:45:22 -0400, "Peter"
<> wrote:

>"David J Taylor" <david-> wrote in message
>news:i1rugq$sum$...
>> "DanP" <> wrote in message
>> news:46365b3d-a169-4fa0-8995-...
>> []
>>> The information from an IR image has nothing to do with the colour.
>>> A hot green mug will look different in IR than a plant with the same
>>> shade of green.
>>> So you cannot map IR to visible colour.
>>>
>>> DanP
>>
>> Be careful not to confuse near-IR with far-IR. With digital cameras and
>> film it's the region just beyond the red end of the visible spectrum which
>> people call "IR" - a wavelength of ~0.8um. Here, the prime difference is
>> that the reflectance of vegetation is much higher and hence the
>> characteristic appearance of monochrome IR images.
>>
>
>
>Almost!
>Chlorophyll is transparent to waves in the near IR spectrum. Hence it
>appears to be white. Similarly many clothing dyes are transparent in that
>spectrum and also appear white. Particles in the air cause the sky to appear
>blue. In this spectrum these particles do not reflect the energy waves and
>thus appear black.
>
>BTW I have submitted an IR photo in the SI.

I'm glad everyone is enjoying this discussion so much,
although I was pretty much done when I found it that "...it wouldn't
work"
Meanwhile, I've now been convinced that I might be best off to
stay well away from infra-red completely.
Am I to understand that not only would I not be able to
convert the infra-red colors back to "regular" color since there's a
lack of information about the regular color in the infra-red image,
but also that there are things out there that absorb the infra-red and
make using it for photography far more difficult?
I might to to B & W infra-red for photos where I don't want to
distract anyone with flash, but I won't go anywhere near color
infra-red... unless I want to take spooky looking pix that is.

On Fri, 16 Jul 2010 16:36:20 -0700 (PDT), Nervous Nick
<> wrote:

>On Jul 15, 7:48*pm, Scotius <yodas...@mnsi.net> wrote:
>> * * * * I know that color infra-red images look really weird (for lack
>> of a better term), but I once read that infra-red light cuts through
>> fog/haze etc better than regular light, which I suppose is why B & W
>> infra-red shots always look better than B & W shots without IR flash.
>> * * * * So I'm wondering if there's a program that could accurately
>> predict based on IR color what the colors present should be, and
>> convert them, so it would be possible to do color shots better in
>> haze, etc.
>> * * * * Anyone know of anything like this?
>
>Why would you want to do this, even if it were at all possible?

I was recently covering a concert for a local magazine, and
asked a stage manager about taking pix with the flash. He said go
ahead and take a few with flash, but not too many, so as not to be
distracting.
I had read about B & W infra-red photography in an old issue
of Popular Mechanics, I think, that my Dad had lying around somewhere.
Then I had read an article on color infra-red, and I thought "Oh, well
then I'll just shoot pix like that in color infra-red and convert them
on the computer back at home. People can't see infra-red, so there
won't be a visible flash, and I'll convert the pix and have great
shots that didn't bother anyone".
It's since been explained to me that there's no method of
converting the color infra-red pix, since the information about actual
color is just as gone in those as it would be in black and white.
I suppose for a huge event I could take one with flash and
then recolor manually and submit the pix a couple years later , but
that's not really what I was looking to be able to do.

On Jul 28, 4:35*pm, Scotius <yodas...@mnsi.net> wrote:
> On Fri, 16 Jul 2010 16:36:20 -0700 (PDT), Nervous Nick
> >Why would you want to do this, even if it were at all possible?
>
> * * * * I was recently covering a concert for a local magazine, and
> asked a stage manager about taking pix with the flash. He said go
> ahead and take a few with flash, but not too many, so as not to be
> distracting.
....
> * * * * I suppose for a huge event I could take one with flash and
> then recolor manually and submit the pix a couple years later , but
> that's not really what I was looking to be able to do.

It is often not necessary, or even desirable, to take pictures with
flash at a concert. These were taken (not by me) without flash. I
wouldn't say they are great, but it shows that it is at least
possible:

http://www.flickr.com/photos/natalie...7623793453107/
http://www.flickr.com/photos/natalie...7623793453107/

Those were taken with a Rebel Xsi, which I think is similar to your
D3000, as far as sensor size.

You could also get a fast prime lens, or perhaps even a camera with a
FF sensor if you wanted better low-light performance.