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Old Jun 13, 2007, 1:02 AM   #1
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I don't know if this is a big deal or not, but I noticed my A100 has a stuck pixel in the upper left corner. It's away from the center so it's not terribly bothersome, but then I think I'm going to have to correct this pixel in every picture I ever take with this camera (thousands). Is it normal to have something like this?



Shown above at 100% and 1600%.
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Old Jun 13, 2007, 9:27 PM   #2
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If this camera is still under warranty have you considered sending it in for service?
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Old Jun 15, 2007, 4:40 PM   #3
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I bought the camera a little less than a month ago, so I'm pretty sure it'd still be covered under warranty.

Is this common to have a pixel like this and just forget about it, or does it need to be replaced?
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Old Jun 15, 2007, 5:18 PM   #4
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What were your camera settings (shutter speed, ISO speed)?

If slower (i.e., 1 second or longer), was noise reduction turned on? It's entire purpose is to remove hot pixels that usually show up on long exposures using a dark frame subtraction system (most modern cameras will have them on longer exposures).

Not enough light hitting the sensor can also be a contributing factor, and that looks like a lens cap on image.

If you get them in normal lighting at typical shutter speeds, then you can worry, but only if the camera can't take them out for you (there is a built in remap algorithm that does that every new month).

If you want to force it, change the date by setting the month forward and save it. When you power your camera off after using it, you'll notice the access lamp staying on for much longer. It appears to take a 6 second dark frame and uses it to remap hot pixels from reports I've seen from people trying to figure out exactly how it works (it's an undocumented feature).

Set your date back to where it's supposed to be again (and it will probably do a second remap after the next power down since it doesn't seem to care about how the date was changed, just that the month itself changed).

But, the remap function is not designed to map at all hot pixels that would normally appear on longer exposures. That's the purpose of the built in noise reduction system .

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Old Jun 15, 2007, 8:31 PM   #5
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I've noticed it on all my exposures since last weekend. Before that, the pixel was working fine. But starting with the first picture from the last batch I took, they all have the white mark. One I'm looking at right now is F/5.6, 1/640 sec., ISO-400. I don't think it's a hot pixel and noise.

Noise reduction is set at whatever the default is. I haven't played around with that yet.

I'll try the remapping feature.

EDIT: That fixed it! Thanks for posting that, Jim.

Is that pixel back in full working order, or do I have a 10,199,999 pixel sensor now?
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Old Jun 15, 2007, 8:51 PM   #6
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It maps it out so that it no longer contributes to the image. Basically, it replaces it with values from adjacent pixels.

Most cameras have a bad pixel map built into them. The factories map the bad ones out so that you never see them.

The idea is to make sure there is an acceptable number of defects in the conditions you're using the sensor in (light, temperature, ISO speed, shutter speed).

For the defective photosites that are in a camera's sensor at typical conditions, the factory has already mapped them out. So, while you may think your sensor is perfect, chances are, it's not. When users of cameras that develop a bad pixel use software to update the table in EEPROM, they usually see that other pixels were also found (these are the ones that were already mapped out by the factory).

Keep in mind that you've got millions of photosites, and each one is only sensitive to one color anyway (Red, Green or Blue in most Bayer Pattern designs). So, the demosaic/interpolation algorithms are combining values from multiple photosites to store at each pixel location.

As a result, photosites that are not linear in their sensitivity (either too bright or too dark compared to the way they should be), don't have as much impact on a final image when they are remapped.

It's also not uncommon for a CCD to develop more bad pixels as a camera ages (and temperature plays a role, too).

Basically,a manufacturer is keeping a bad pixel table in memory (EEPROM), and it interpolates around them during processing (taking values from adjacent pixels and replacing them).

With older camera models, when you had a bad pixel (either dead or stuck on) the manufacturer's typically ran a service program to update the bad pixel map. Most consumers thought the CCD was being replaced, when the camera's processing is just interpolating to replace the bad ones. ;-) Some models only do this with jpeg data, and some also replace data in raw files.

You can find software to update some models yourself now (for a number of consumer cameras made by Nikon, Olympus and others). You can even find software to update the bad pixel table in some DSLR models (for example, the Nikon D100). This software is not supported by the manufacturers (hackers figured out how to call the hidden routines in the cameras).

Here is one example that can work with some of the Nikon and Olympus consumer models (and I've got software to do it for the Nikon D100, too; and I know of someone that has the factory service software for some older Canon DSLR models).

http://e2500.narod.ru/ccd_defect_e.htm

With some newer cameras, the manufacturers started finding a way to let the camera do it without the need for separate service software. Olympus started it first (AFAIK), beginning with their Olympus E10 Model (this 4MP 2/3" Olympus desginedCCD was very bad for getting stuck pixels, so they came out with a firmware upgrade designed to call a service routine to check for them and map them out. Many newer models from Olympus now have a menu choice to remap bad pixels (even though they're not using Olympus designed sensors anymore).

Konica Minolta put in an Automatic routine to check for bad pixels and map them out monthly in some of their newer models. I've never seen it officially confirmed. But, more than one user has reported that it works. Sony retained this feature with the DSLR-A100.

I've also seen it reported that some Canon DSLR models do a remap when the mirror is locked up for cleaning.

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Old Jun 16, 2007, 1:41 AM   #7
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looks more like dust on the chip
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Old Jun 16, 2007, 8:29 AM   #8
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The above crop is a hot pixel (brighter than it should be, and easily visible against a dark background). When it remains hot regardless of shutter speed, it's considered to be "stuck" (always hot).

This is what dust looks like (more easily visible against a bright background at smaller apertures). Most people notice it in photos with lots of bright sky first.

http://forums.steves-digicams.com/fo...amp;forum_id=2


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Old Jun 16, 2007, 11:31 AM   #9
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at least you only have one..
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Old Jun 16, 2007, 11:41 AM   #10
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i did note that at faster speeds there were less....



nothing i'm going to cry over...nothing is more than a click away from perfect..:?
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