by Nereid » Fri Oct 24, 2008 4:11 pm
emc wrote:Nereid wrote:[snip]...No doubt Sputnick (and emc?) does not count these three kinds of digital alteration...[snip]
Hi Neried,
Just wanted to try and clear your question mark beside my username…. BTW – you can call me Ed if you like. I used emc because it seemed be appropriate for identifying the typist when I signed up to the forum.
All images on my computer screen are digitally “altered” in several ways from the “real” world. I don’t have a problem with any of that and I would not enjoy the APODs as much if they were stark.
It seems to me that regardless of the filtering from saturation from cosmic ray hits and all the other data processing physics… electrons, photons, lenses, CCDs, film, internet, etc., that the images could be displayed in an “enhanced” version that simulates the human visible spectrum. I think it would add an interesting dimension to occasionally see the “normal” human eye version in overlay or underlay of an APOD. Are you telling us that this is not possible?
Hi Ed,
Not sure if you'd read Chris' excellent post before you wrote this (that I'm quoting), but anyway ...
Let's parse APODs a bit first; let's exclude all APODs that are 'of Earth, from Earth' (
example), and 'from Earth using just an ordinary camera' (
example,
example - note that even those taken with colour film do not precisely convey what your eyes would see if only you'd been there at the time), all those which include a component beyond the visual waveband, and all those which include a 'narrow band filter' component. That's quite a significant fraction of all APODs by the way.
With the caveat that some aspects are not 100% faithful wrt what the human eye would see (e.g. contrast and brightness), many APODs of the Moon would fit your request, whether taken from Earth (
example) or off it (
example).
Ditto for planets and moons other than Earth and the Moon, with the caveat about enhanced contrast and boosted colours perhaps stressed, some examples:
Mars from Earth, another
Mars from Mars,
Saturn,
Rhea.
I'll skip the Sun.
Stars (other than the Sun)? Here's where one's individual sense of what's OK wrt the inevitable differences between images obtained using telescopes and cameras and what your eye would see becomes important. For example, your eye never sees diffraction spikes (
Pleiades example) so all images with them visible automatically fail to meet your criteria. Colours are just as problematic;
here's the Pleiades without diffraction spikes but I think the colour contrast is far too great (and the intensity contrast far too unreal), and
here's another example - if the intensity were sufficient to excite the cones in your eyes, I expect the perceived colours would be subtle.
For galaxies there's no doubt: what the human eye sees, even with excellent equipment and dedication, is nothing like almost all APODs - if you live in the southern hemisphere, take a look at the Magellanic Clouds from a dark site (on a moonless night), that's what galaxies look like.
Nebulae - planetary, HII, supernova remnants, etc - present their own, unique, challenges. There's a lively discussion in some amateur circles about how to accurately photograph (or represent) the colours in these, especially planetaries dominated by the [OIII] lines. Leaving aside questions of contrast and intensity, the difficulty is that for many of these nebulae most (almost all) the visible light comes from just a few lines, such as the green lines of [OIII]. So to get an accurate (= faithful to what the eye would see) representation, the filter/detector/processing must accurately match the human rods+cones+visual system response wrt those lines ... and that's very difficult! There may be some APODs which succeed; does any reader know of any?
[quote="emc"][quote="Nereid"][snip]...No doubt Sputnick (and emc?) does not count these three kinds of digital alteration...[snip][/quote]
Hi Neried,
Just wanted to try and clear your question mark beside my username…. BTW – you can call me Ed if you like. I used emc because it seemed be appropriate for identifying the typist when I signed up to the forum.
All images on my computer screen are digitally “altered” in several ways from the “real” world. I don’t have a problem with any of that and I would not enjoy the APODs as much if they were stark.
It seems to me that regardless of the filtering from saturation from cosmic ray hits and all the other data processing physics… electrons, photons, lenses, CCDs, film, internet, etc., that the images could be displayed in an “enhanced” version that simulates the human visible spectrum. I think it would add an interesting dimension to occasionally see the “normal” human eye version in overlay or underlay of an APOD. Are you telling us that this is not possible?[/quote]
Hi Ed,
Not sure if you'd read Chris' excellent post before you wrote this (that I'm quoting), but anyway ...
Let's parse APODs a bit first; let's exclude all APODs that are 'of Earth, from Earth' ([url=http://antwrp.gsfc.nasa.gov/apod/ap081001.html]example[/url]), and 'from Earth using just an ordinary camera' ([url=http://antwrp.gsfc.nasa.gov/apod/ap080926.html]example[/url], [url=http://antwrp.gsfc.nasa.gov/apod/ap080809.html]example[/url] - note that even those taken with colour film do not precisely convey what your eyes would see if only you'd been there at the time), all those which include a component beyond the visual waveband, and all those which include a 'narrow band filter' component. That's quite a significant fraction of all APODs by the way.
With the caveat that some aspects are not 100% faithful wrt what the human eye would see (e.g. contrast and brightness), many APODs of the Moon would fit your request, whether taken from Earth ([url=http://antwrp.gsfc.nasa.gov/apod/ap071025.html]example[/url]) or off it ([url=http://antwrp.gsfc.nasa.gov/apod/ap071120.html]example[/url]).
Ditto for planets and moons other than Earth and the Moon, with the caveat about enhanced contrast and boosted colours perhaps stressed, some examples: [url=http://antwrp.gsfc.nasa.gov/apod/ap080714.html]Mars from Earth[/url], another [url=http://antwrp.gsfc.nasa.gov/apod/ap061002.html]Mars from Mars[/url], [url=http://antwrp.gsfc.nasa.gov/apod/ap070526.html]Saturn[/url], [url=http://antwrp.gsfc.nasa.gov/apod/ap060530.html]Rhea[/url].
I'll skip the Sun.
Stars (other than the Sun)? Here's where one's individual sense of what's OK wrt the inevitable differences between images obtained using telescopes and cameras and what your eye would see becomes important. For example, your eye never sees diffraction spikes ([url=http://antwrp.gsfc.nasa.gov/apod/ap060109.html]Pleiades example[/url]) so all images with them visible automatically fail to meet your criteria. Colours are just as problematic; [url=http://antwrp.gsfc.nasa.gov/apod/ap071118.html]here's the Pleiades without diffraction spikes[/url] but I think the colour contrast is far too great (and the intensity contrast far too unreal), and [url=http://antwrp.gsfc.nasa.gov/apod/ap080826.html]here's another example[/url] - if the intensity were sufficient to excite the cones in your eyes, I expect the perceived colours would be subtle.
For galaxies there's no doubt: what the human eye sees, even with excellent equipment and dedication, is nothing like almost all APODs - if you live in the southern hemisphere, take a look at the Magellanic Clouds from a dark site (on a moonless night), that's what galaxies look like.
Nebulae - planetary, HII, supernova remnants, etc - present their own, unique, challenges. There's a lively discussion in some amateur circles about how to accurately photograph (or represent) the colours in these, especially planetaries dominated by the [OIII] lines. Leaving aside questions of contrast and intensity, the difficulty is that for many of these nebulae most (almost all) the visible light comes from just a few lines, such as the green lines of [OIII]. So to get an accurate (= faithful to what the eye would see) representation, the filter/detector/processing must accurately match the human rods+cones+visual system response wrt those lines ... and that's very difficult! There may be some APODs which succeed; does any reader know of any?