IPB

Welcome Guest ( Log In | Register )

4 Pages V  < 1 2 3 4 >  
Reply to this topicStart new topic
Global True Color View Of Venus?
JRehling
post Aug 26 2005, 03:50 PM
Post #16


Senior Member
****

Group: Members
Posts: 1572
Joined: 20-April 05
Member No.: 321



QUOTE (tedstryk @ Aug 26 2005, 08:25 AM)
Sounds like an extended mission task.  16 km was the resolution/pixel, 50-100 was the estimated realistic resolution, thanks to the atmosphere.  I am just hoping that the predictions don't hold up  cool.gif
*


I'm worried more about the spectral resolution -- All the Galileo image really shows is that areas of higher altitude are cooler, and if all we get out of this is thermal information at >10 km resolution, it'll be of very little interest.

Even with excellent data, spectral resolution has a tough time converting into mineralogy (note TES @ Mars, and the very vague assessments of the non icy compositions of the Galileans). In the case of Venus, we'll have so much spectral interference from numerous species (some unknown!) not to mention thermal noise, really the best I hope for is that we get a good cumulative, length-of-mission differentiation between planitia, tessera, fresh lava flows, and the radar-bright areas at high altitudes. Anything evidentiary about mineralogy between those four unit types would be great, and the recognition of any units that show up in IR but not in radar would be a godsend.

As far as eye candy goes, the best we could dream of would be to get low res data that could be used to "color" the radar maps illustratively or realistically.

One good subcloud aerobot with a camera would take a much better whack at this, with an easy time of making visible light spectra on the surface unit level, if not decameter level. Hopefully soon...
Go to the top of the page
 
+Quote Post
Guest_BruceMoomaw_*
post Aug 29 2005, 12:39 AM
Post #17





Guests






I promised fully 2 months back to dig up whatever stuff I had on the possible ability of VIRTIS to map surface composition, and I'm putting up that entry now back on the "Venus Express" thread.
Go to the top of the page
 
+Quote Post
t_oner
post Dec 4 2005, 06:41 PM
Post #18


Junior Member
**

Group: Members
Posts: 97
Joined: 26-September 05
Member No.: 508



It is unbelievable that Venus is the nearest planet and we still don't have a single global true color image of it. Galileo could have done it but did not, I don't know if Cassini could do it because of technical issues. It may or not have a scientific value but it should be done. I hope Venus Express has a suitable camera and filters for this job. (Pluto not yet explored, Venus not yet explored in true color).
Go to the top of the page
 
+Quote Post
JRehling
post Dec 5 2005, 02:03 AM
Post #19


Senior Member
****

Group: Members
Posts: 1572
Joined: 20-April 05
Member No.: 321



QUOTE (Tayfun Íner @ Dec 4 2005, 10:41 AM)
It is unbelievable that Venus is the nearest planet and we still don't have a single global true color image of it. Galileo could have done it but did not, I don't know if Cassini could do it because of technical issues. It may or not have a scientific value but it should be done. I hope Venus Express has a suitable camera and filters for this job. (Pluto not yet explored, Venus not yet explored in true color).
*


We don't have many great pictures of the far side of the Moon in true color, and not very many near-full phase pictures of the Earth in true color!

As I mentioned earlier, there are some pretty good pictures of Venus taken from Earth, in which case, it is never a full Venus, but at least we can start to imagine the real deal!

FWIW, Mercury is the third-nearest planet, and the impoverishment of good imagery there in anything approximating true color is astonishing. Even FROM Earth!
Go to the top of the page
 
+Quote Post
Guest_DonPMitchell_*
post May 5 2006, 08:49 PM
Post #20





Guests






There is a spectral albedo for Venus. That can be turned into XYZ, via the CIE tables. Then convert that into Standard RGB ("sRGB"), which is a set of phosphor chromas that the computer industry and the HDTV people all more or less agree on. It has a gamma of 2.2.

Here's a set of planet colors, with brightnesses proportional to the total albedo:Planetary Palette
Go to the top of the page
 
+Quote Post
JRehling
post Oct 12 2007, 10:32 PM
Post #21


Senior Member
****

Group: Members
Posts: 1572
Joined: 20-April 05
Member No.: 321



QUOTE (elakdawalla @ Aug 8 2005, 11:53 AM) *
I'm creating a website with views of the worlds of the solar system, to scale with each other (it'll march up and down the few orders of magnitude necessary), and I am having a terrible time finding a global view of Venus to include in it that fits the criteria I'm trying to apply. To the extent possible, I am searching for:

- Full-disk, global view
- Minimum phase angle available
- Approximate true color, as would be perceived by a human observing the globe from space


[resurrecting a long-dead thread]
The lack of this has always bothered me. Messenger took an image of an almost full Venus, but cropped two edges, and only the plain filter image was made public.

Thanks to the blandness of Venus, it's not too hard to patch that image up. I used its own north end to fill in the cropped-out south and used a Titan image (appropriately tweaked from orange to BW) to sub in the cropped-out west. Then I took an amateur's earth-based image to find the right color balance. And... voila. A little bit of fiction is involved, but I think it fits the above criteria, that said.
Go to the top of the page
 
+Quote Post
scalbers
post Oct 12 2007, 10:52 PM
Post #22


Member
***

Group: Members
Posts: 815
Joined: 5-March 05
From: Boulder, CO
Member No.: 184



Well, I guess this wouldn't be true color, yet the past two issues of Sky and Telescope magazine have had some nice Venus shots from Earth. These show some cloud features utilizing ultraviolet filters.


--------------------
Go to the top of the page
 
+Quote Post
Gladstoner
post Jan 4 2008, 09:05 AM
Post #23


Member
***

Group: Members
Posts: 206
Joined: 3-January 08
Member No.: 3995



.
Go to the top of the page
 
+Quote Post
4th rock from th...
post Dec 29 2008, 01:08 PM
Post #24


Member
***

Group: Members
Posts: 304
Joined: 21-April 05
From: Portugal
Member No.: 347



Hi all,

I've updated my webpage with some Venus Express images processed in approximate real color.

The images seem to show the Venusian atmosphere extending from the limb with a bluish color. The general tone of the planet is yellowish, in accordance to similar processing I've done with Mariner 10 images, available on this site. The brightest clouds are bluish, given that they reflect strongly on the UV parts of the spectrum.

RGB channels were computed from NIR1, VIS and UV images using the following averages:

Red = 0.3 x NIR1 + 0.7 x VIS = 0.3 x 965 + 0.7 x 513 = 649
Green = VIS = 513
Blue = 0.5 x VIS + 0.5 x UV = 0.5 x 513 + 0.5 x 365 = 439

Here's one image, you can see more at http://www.astrosurf.com/nunes/explor/explor_vex.htm



--------------------
_______________________
www.astrosurf.com/nunes
Go to the top of the page
 
+Quote Post
ugordan
post Jun 1 2009, 06:48 PM
Post #25


Senior Member
****

Group: Members
Posts: 3570
Joined: 1-October 05
From: Croatia
Member No.: 523



I've been messing around with the MESSENGER calibrated data and even though it's not a complete global view, I thought I'd share it here. From the filter choice standpoint, it's the closest we get to a RGB image for the time being. I already posted a few of those in the MESSENGER PDS threads, but those were quick-n-dirty versions.

Below is the familiar inbound view by the wide-angle camera, but this time I approached it somewhat differently. Instead of the typical E/D/C "red/green/blue" filter combo, I used E/D/F. Even though the "F" filter is labeled as violet, at 430 nm central wavelength it's actually much closer to the peak sensitivity of the blue light-sensitive cones in the human eye (437 nm). The "C" filter is shifted way too much toward green at 480 nm and also much more narrowband. Venus composites using the "blue" filter as a result fail to capture the bright clouds that reflect strongly in the UV, while the "F" filter does exactly that while still being inside human vision boundaries, i.e. not being UV.

I used the ground calibration tables when calibrating the data as the inflight-derived results look inconsistent across filters to me. Next, I took the central filter wavelengths and compared them to the sRGB colospace central wavelengths. I calculated approximate channel mixes to bring the "average" wavelength in all 3 RGB channels to sRGB, this is what I used:

red = 0.72*E + 0.28*D
grn = 0.93*D + 0.07*F
blu = 0.73*F + 0.27*D

Finally, I boosted saturation by +15 to compensate for a slight loss of saturation by above mixing.

Here is the resulting composite:
Attached Image


It looks as it's in the same ballpark as some other versions here. This one is not gamma-corrected because absolutely all contrast would be washed out and you'd end up with a shiny white billiard ball.

Here's a high-pass enhancement to bring the clouds out a bit:
Attached Image


--------------------
Go to the top of the page
 
+Quote Post
Stu
post Jun 1 2009, 08:48 PM
Post #26


The Poet Dude
****

Group: Moderator
Posts: 5548
Joined: 15-March 04
From: Kendal, Cumbria, UK
Member No.: 60



Absolutely beautiful images, thanks for posting them here. Hope you won't mind me using them in my talks? That second one is just sublime.


--------------------
Go to the top of the page
 
+Quote Post
ugordan
post Jun 1 2009, 09:08 PM
Post #27


Senior Member
****

Group: Members
Posts: 3570
Joined: 1-October 05
From: Croatia
Member No.: 523



Sure, no problem at all, Stu. Glad you like them.


--------------------
Go to the top of the page
 
+Quote Post
4th rock from th...
post Jun 2 2009, 09:55 AM
Post #28


Member
***

Group: Members
Posts: 304
Joined: 21-April 05
From: Portugal
Member No.: 347



QUOTE (ugordan @ Jun 1 2009, 06:48 PM) *
... I calculated approximate channel mixes to bring the "average" wavelength in all 3 RGB channels to sRGB...
...This one is not gamma-corrected because absolutely all contrast would be washed out and you'd end up with a shiny white billiard ball.
....


Nice results. I think that the channel mixing to average center wavelenght works very very well and can be used with almost any filter set. I'm not shure it saturation suffers that much, because that would have more to do with each filter bandwidth. Nevertheless, results are consistent. I think that you could include a gamma corrected version, because that would show exactly why the details are dificult to see at the telescope. It would also be closer to what we might see if in orbit of the planet.


--------------------
_______________________
www.astrosurf.com/nunes
Go to the top of the page
 
+Quote Post
ugordan
post Jun 2 2009, 10:15 AM
Post #29


Senior Member
****

Group: Members
Posts: 3570
Joined: 1-October 05
From: Croatia
Member No.: 523



QUOTE (4th rock from the sun @ Jun 2 2009, 11:55 AM) *
I think that you could include a gamma corrected version, because that would show exactly why the details are dificult to see at the telescope. It would also be closer to what we might see if in orbit of the planet.

Well, you asked for it:
Attached Image


This was done on the 8 bit PNG above, not the 16 bit one I worked with as I'm at work now, but this only induces a slightly higher noise near the terminator. I continue to be amazed at just how sharply defined the planet's limb is. It really looks like someone put a solid ball in space - no limb brightening or other Rayleigh scattering effects.


--------------------
Go to the top of the page
 
+Quote Post
Stu
post Jun 2 2009, 10:35 AM
Post #30


The Poet Dude
****

Group: Moderator
Posts: 5548
Joined: 15-March 04
From: Kendal, Cumbria, UK
Member No.: 60



Wow, there really would be b****r all to see if you went there, wouldn't there? Makes Uranus look positively psychedelic! laugh.gif


--------------------
Go to the top of the page
 
+Quote Post

4 Pages V  < 1 2 3 4 >
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 1st November 2014 - 01:15 AM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.