white cross, hot pixels: Noise or something else?
In some low light shots I've made, there seems to be a four pixel green cross that shows up on some shots under similar situations.
Properly exposed photographs do not have this problem...
Is there a way to make a distinction between a hot pixel and noise from underexposed areas?
#2. "RE: white cross, hot pixels: Noise or something else?" | In response to Reply # 0dstoerm Registered since 23rd Mar 2006Mon 22-May-06 11:54 PM
We have seen this 'cross' on our D200s. Is the center pixel in the cross brighter than the adjacent 4-8 pixels in the cross? If so, it is a dying photosite in the sensor - picture a star about to go supernova!
Map the site if possible, and forward it to Nikon USA. They are unfortunately aware of this and they know what to do (replace the CCD since mapping it out will not stop the current draw to the affected area on the chip). It seems that their sensors from Sony have been somewhat "Less than we were hoping for"-Nikon.
Expose the CCD sensor without light, ie lenscap, and see the horror up close - you may have to look very close in this case, but the sensor is in the process of dying. Your cross will grow and grow and grow with more current directed to the photo site on the CCD.
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#3. "RE: white cross, hot pixels: Noise or something else?" | In response to Reply # 2bclaff Registered since 25th Oct 2004Tue 23-May-06 12:26 AM
Well... that's a colorful description!
Current leakage at a (single) photosite will make that photosite appear too bright.
The demosaicking algorithm, which converts the red, green, or blue photosites into red, green, and blue pixels works by "consulting" neighboring photosites.
So one bad photosite affects it's neighbors, especially the 4 (or 8) closest.
This leads to the classic "cross", in bad cases the diagonal pixels get affected too.
This will not spread as the center photosite gets worse; but it's usually bad enough without spreading!
(In other words, in my experience it's unlikely to get dramatically worse but it's bad enough already.)
As Far As I Know (AFAIK) Nikon has been outsourcing to Sony for quite some time.
But I agree that the D200 sensor seems far more prone to bad photosites than the other Nikon DSLR sensors.
We might be flirting with a "bleeding edge" design in our D200s.
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#4. "RE: white cross, hot pixels: Noise or something else?" | In response to Reply # 33XP05UR3 Registered since 29th Mar 2006Tue 23-May-06 12:54 AM
wow that's really dramatic stuff.
I've actually already had my CCD replaced once before a host of problems, including bad photosites.
BUT this is different. I did the lens cap test at 3". No hot pix. What's strange is that it only showed up on a few low light/underexposed areas of the picture but it had the configuration of a bad photosite.
Again, properly exposed shots and now a lens cap test shows no problem...