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Black Sun
Hi everyone! I am trying to observe the sun using a CMOS chip, but I get the following problem: when the neutral density located in front of the sensor is too low, a "black hole" appears at the center of the sun. Have you already met this kind of problem? Is it a known phenomenon? I have tried to search for information concerning this type of problem on the web, but I did not find any clues how to solve it. It seems that this "black sun" can also appear with CCD chips. Is there a way to solve it without using post image processing? Cedric |
#2
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Black Sun
In article om,
murlockc wrote: Hi everyone! I am trying to observe the sun using a CMOS chip, but I get the following problem: when the neutral density located in front of the sensor is too low, a "black hole" appears at the center of the sun. Have you already met this kind of problem? Is it a known phenomenon? I have tried to search for information concerning this type of problem on the web, but I did not find any clues how to solve it. It seems that this "black sun" can also appear with CCD chips. Is there a way to solve it without using post image processing? Cedric It would depend on which CMOS sensor your talking about. I know that Zoran CMOS sensors had that issue and when we looked at light bulbs the filament would appear black. Changing the intensity of the gains helped somewhat but it was an electronics issue and had to be resolved post. HTH.. Milton Aupperle http://www.outcastsoft.com/AstroImages/AstroIndex.html |
#3
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Black Sun
murlockc wrote:
Hi everyone! I am trying to observe the sun using a CMOS chip, but I get the following problem: when the neutral density located in front of the sensor is too low, a "black hole" appears at the center of the sun. Have you already met this kind of problem? Is it a known phenomenon? I have tried to search for information concerning this type of problem on the web, but I did not find any clues how to solve it. It seems that this "black sun" can also appear with CCD chips. Is there a way to solve it without using post image processing? Cedric This is what you can expect when you burn in the ccd chip. I had it happen with a ccd camera observing/recording the road in front of a touring car. Just when the sun came up, the bus had to stop for 2 minutes, with the sun just over the horizon. And that was the end of the camera, with black spots all over the place, not actual breaking down, but almost total loss of sensitivity in spots. |
#4
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Black Sun
On 28 Sep 2006 06:47:09 -0700, "murlockc" wrote:
Hi everyone! I am trying to observe the sun using a CMOS chip, but I get the following problem: when the neutral density located in front of the sensor is too low, a "black hole" appears at the center of the sun. Have you already met this kind of problem? Is it a known phenomenon? I have tried to search for information concerning this type of problem on the web, but I did not find any clues how to solve it. It seems that this "black sun" can also appear with CCD chips. Is there a way to solve it without using post image processing? This problem is usually one with the camera electronics. Each pixel produces a charge proportional to how much light it collects, and this charge is converted to a number by an analog-to-digital converter. Some ADCs can produce invalid codes (for instance, they can wrap around to small values when their input goes above some level), and some of the other electronics or software can create similar problems (by redefining the zero point, or by not properly handling an internal conversion to 8 bits from whatever the internal resolution is). Regardless of the exact cause, it means you are effectively saturating those pixels, and the fix doesn't involve processing. You need to reduce the number of photons, either by adding more optical filtering or by reducing your exposure time. With regards to any data you already have, some information may be recoverable assuming the problem is one of wrap-around. You need to add your saturation value (for instance, 255 for an 8-bit webcam) to the artificially dark pixels. Of course, you need to do this in something larger than an 8-bit workspace. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#5
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Black Sun
There is an effect in regular silver photography that when the grains
are seriously over exposed that a reversal occurs. I think this is called the Clayden effect. Chris L Peterson wrote: On 28 Sep 2006 06:47:09 -0700, "murlockc" wrote: Hi everyone! I am trying to observe the sun using a CMOS chip, but I get the following problem: when the neutral density located in front of the sensor is too low, a "black hole" appears at the center of the sun. Have you already met this kind of problem? Is it a known phenomenon? I have tried to search for information concerning this type of problem on the web, but I did not find any clues how to solve it. It seems that this "black sun" can also appear with CCD chips. Is there a way to solve it without using post image processing? This problem is usually one with the camera electronics. Each pixel produces a charge proportional to how much light it collects, and this charge is converted to a number by an analog-to-digital converter. Some ADCs can produce invalid codes (for instance, they can wrap around to small values when their input goes above some level), and some of the other electronics or software can create similar problems (by redefining the zero point, or by not properly handling an internal conversion to 8 bits from whatever the internal resolution is). Regardless of the exact cause, it means you are effectively saturating those pixels, and the fix doesn't involve processing. You need to reduce the number of photons, either by adding more optical filtering or by reducing your exposure time. With regards to any data you already have, some information may be recoverable assuming the problem is one of wrap-around. You need to add your saturation value (for instance, 255 for an 8-bit webcam) to the artificially dark pixels. Of course, you need to do this in something larger than an 8-bit workspace. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#7
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Black Sun
Solarization is during or after partial development. I wonder if there
was a partial light leak in the system to slightly expose the system the followed by major over exposure. Just a thought, but I would look for a small light leak. Chris L Peterson wrote: On 5 Oct 2006 14:08:24 -0700, wrote: There is an effect in regular silver photography that when the grains are seriously over exposed that a reversal occurs. I think this is called the Clayden effect. Silver? Grains? g Seriously, I think the effect with film would be better described as solarization. The Clayden effect is associated with a reversal that occurs when making a normal exposure after the film is exposed to a brief, high intensity flash. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#8
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Black Sun
On 7 Oct 2006 08:10:14 -0700, wrote:
Solarization is during or after partial development. I wonder if there was a partial light leak in the system to slightly expose the system the followed by major over exposure. Just a thought, but I would look for a small light leak. Discussing the details of obscure artifacts in obsolete technology is interesting, but the OP is using an electronic sensor, so none of them apply in his case. His problem is almost certainly related to errors in mapping between pixel charge and ADUs. A light leak wouldn't cause his problem (and in fact, what he is seeing is a common artifact of low end digital cameras). _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
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