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Post by JayUtah on Aug 11, 2009 10:11:57 GMT -4
DCT compression is not invertible. It is possible to mitigate the visual effects of DCT compression, but that process does not recover the original data.
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Post by gonetoplaid on Aug 11, 2009 11:15:47 GMT -4
DCT compression is not invertible. It is possible to mitigate the visual effects of DCT compression, but that process does not recover the original data. Thanks for the info Jay. Well, that sucks. I guess I need to contact NASA and see if I can download TIFFs. |
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Post by ka9q on Aug 12, 2009 1:34:41 GMT -4
I've noticed those blue dots too. They're quite common throughout all (or at least most) missions, and they appear in front of dark foreground objects, proving that they're not "crystal palaces" or whatever the nutters want to see in the background sky.
That they might be cosmic ray hits occurred to me too, but if they were I'd expect them to be streaks in random directions. But they're not. They're either dots or vertical streaks in the direction the film moved in the magazine.
Ah ha - that pretty much settles the issue. Either they were scratches from dust grains caught between the reseau plate and the film, or they were static discharges that occurred as the film was wound in a very dry (by definition) vacuum.
Why blue? Well, in Ektachrome, the blue-sensitive layer is on top of the emulsion, so it's first to be damaged. Scraping the blue emulsion away has the same effect as exposing it to bright blue light: the silver halide all becomes silver in development and is then bleached away. Nothing is left after the reversal to form yellow dye in that layer to stop blue light. If the middle (green) and bottom (red) layers are intact and unexposed, they form magenta and cyan dye, the subtractive intersection of which is blue. So the dot or scratch appears blue.
I note that deeper scratches turn white, probably because they remove all three layers of the emulsion.
It would be worth examining magazines of the same type of film (SO-368, basically a type of Ektachrome) that never went to the surface. Problem is, this may not help us distinguish between these two possibilities because the magazines not used on the dirty surface also weren't advanced in a vacuum. Maybe we should look for magazines that were taken to the moon, brought back to orbit and then used in the CSM. If the dots and streaks first appear on the moon and continue after return to the CSM, then it's most likely trapped lunar dust.
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Post by gonetoplaid on Aug 12, 2009 1:54:50 GMT -4
^^ Ka9q, that is positively brilliant logical deduction which leads to your very interesting hypotheses. It also occured to me, after reading your remarks, that dust could indeed get trapped between the film and the Reseau plate or between layers of film as the film got tightly wound around the take-up spool. I too had wondered why I mostly see blue dots and very few blue streaks. One possibility is that cosmic rays entered through the lens since the film magazines were beefed up with thicker metal. That also would help to explain why we see mostly dots. The problem with this idea is that we should see other color combination dots from time to time too since cosmic rays can be fickle about what they finally end up interacting with. Your dust and/or static discharge hypotheses seem to make the most sense.
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Post by JayUtah on Aug 12, 2009 13:42:58 GMT -4
Somewhere on Clavius I have the results of progressively deeper scratches on Ektachrome film. Yes, it creates an image that starts blue (shallow) and progresses to white (deep).
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Post by ka9q on Aug 13, 2009 2:24:36 GMT -4
One possibility is that cosmic rays entered through the lens since the film magazines were beefed up with thicker metal.That also would help to explain why we see mostly dots. The problem with this idea is that we should see other color combination dots from time to time too since cosmic rays can be fickle about what they finally end up interacting with. Your dust and/or static discharge hypotheses seem to make the most sense. Cosmic ray particles are typically so energetic that it really wouldn't matter whether they went through the lens or the sides of the camera. Not much on a spacecraft can stop them. It's my understanding that the reseau plates were only on the lunar surface cameras; is that true? We could look to see if the blue dots and streaks are more common on images taken with reseau plates. |
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Post by ka9q on Aug 13, 2009 2:50:58 GMT -4
Somewhere on Clavius I have the results of progressively deeper scratches on Ektachrome film. Yes, it creates an image that starts blue (shallow) and progresses to white (deep). I couldn't find it with your search box. |
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Post by grmcdorman on Aug 13, 2009 9:12:28 GMT -4
Doesn't show up with a Google search (site:clavius.org scratch), either. A search for "Ektachrome scratch" doesn't turn up much either.
I do remember a thread, either here or on BAUT, where the topic was discussed, though.
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Post by JayUtah on Aug 13, 2009 9:57:00 GMT -4
I think now it was an attachment on the BAUT thread.
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Post by gonetoplaid on Aug 13, 2009 18:17:30 GMT -4
...It's my understanding that the reseau plates were only on the lunar surface cameras; is that true? We could look to see if the blue dots and streaks are more common on images taken with reseau plates. The Zeiss 60mm Biogon lens was made commercially available sometime after the beginning of the Apollo missions. The lens included the built-in reseau plate. I guess we need to ask some photographers who regularly used this lens if their films had scratches and pinholes due to dust. |
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Post by JayUtah on Aug 13, 2009 18:50:08 GMT -4
The reseau plate and the lens are in completely different parts of the camera. The reseau plate is a standard Hasselblad feature of the data-acquisition variant of their medium-format cameras. It was available before Apollo and is still available. The Zeiss Biogon has undergone a number of design revisions, but is still fundamentally the same optical design.
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Post by trebor on Aug 13, 2009 18:57:58 GMT -4
Speaking of stars in the image AS11-40-5869 of Buzz coming down the ladder there are several 'stars' in the sky, these seem to be in several other shots in the sequence but in different locations.
What is the cause of these?
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Post by Ginnie on Aug 13, 2009 20:11:15 GMT -4
I don't think they are stars, at least they don't photograph consistently. Here is the sequencve of AS11-40-5866/67/68/69 and I've highlighted with a white dot the most visible of these "stars". There seems to be no pattern from one photo to the other. I ignored the fainter blue dots in the photos.  |
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Post by gonetoplaid on Aug 13, 2009 20:38:48 GMT -4
Ginnie, you are correct that those are not stars in that photo sequence. I wrote a spreadsheet program to calculate the angles between all "stars" which I found in those images. None of them could be correlated with any real stars in the visible sky at the Apollo 11 landing site for the given date and time. I even tried aligning and blinking the images to see if there were any real yet extremely faint star images which did match up. That was a "no-go" (as I expected) since the exposure time was just too short and since the 60mm Biogon lense's maximum aperture is just a mere F/5.6 compared to a "fast" lens of F/1 to F/2.
Neat to see that you thought along the same lines as I did though!
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Post by Ginnie on Aug 13, 2009 21:28:41 GMT -4
Ginnie, you are correct that those are not stars in that photo sequence. I wrote a spreadsheet program to calculate the angles between all "stars" which I found in those images. None of them could be correlated with any real stars in the visible sky at the Apollo 11 landing site for the given date and time. I even tried aligning and blinking the images to see if there were any real yet extremely faint star images which did match up. That was a "no-go" (as I expected) since the exposure time was just too short and since the 60mm Biogon lense's maximum aperture is just a mere F/5.6 compared to a "fast" lens of F/1 to F/2. Neat to see that you thought along the same lines as I did though! I had the same kind of thing happen before in regards to a video still of the LM taking off on of the missions. Someone mentioned about stars being in the background - and it did appear that way. But once I viewed the video I could see that the "stars" stayed in the same position in the frame even when the the camera zoomed. So is was dust on the lens or something. |
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