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Old Sep 6, 2009, 10:18 AM   #1
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Default New Sony A200 Hotpixels problem - Serios Build quality issues

Hi All,

I have recently purchased a brand new Sony A200 from an authorised dealer with proper documents and a 3 year warranty.

To my horror the camera has ~20 hotpixels (I verified on the 77th shot, if someone is interested I will post the picture). Is it normal for a brand new DSLR to have such a high number of hotpixels?

Please advice.

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Old Sep 6, 2009, 10:36 AM   #2
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Location: Savannah, GA (USA)
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With what camera settings (iso speed, shutter speed) and in what lighting?

Yes, please post an example. I strongly suspect you're jumping to the wrong conclusions. For example, they're not really bright enough to be considered hot, and you're just seeing a bit of noise instead (possibly due to inappropriate camera settings, underexposing the image by not using a long enough shutter speed, etc.).

I'd make sure you retain the EXIF information so that we can see camera settings used (for example, if long exposure noise reduction was turned on or not so that the camera is performing a dark frame subtraction process).

Most cameras are going to have a number of hot pixels on longer exposures. You just don't see them because they're being mapped out by dark frame subtraction.

With some non-dSLR models, it's not uncommon to see hundreds of them on exposures much over a second if long exposure NR is turned off. Most dSLR models do better.

Virtually all sensors will have them in some conditions. The longer the shutter is open, the more likely a photosite won't be linear with it's fill factor, and it will record a higher value faster than it should.

You just don't see them with most newer cameras because of built in noise reduction to subtract them out on longer exposures (if you have it turned on), since the ones that occur at typical shutter speeds have already been mapped out at the factory.

With most cameras, it only engages on photos taken longer than 1 second (where hot pixels usually show up).

The way it works is by taking two photos. The first photo is of your subject. Then the camera automatically takes a second image using the same settings with the shutter closed.

The camera then notes the positions of any hot (bright) pixels in the "dark frame" (second) exposure, and maps them out of the actual exposure by interpolating values from surrounding pixels to replace the hot ones.

It knows where to find them because the dark frame exposure was taken at the same time, using the same settings, with the camera at the same temperature. In most cases the hot pixel locations will be the same in both images using this technique. But, the longer the exposure, the greater the chance it will miss some of them.

This type of noise reduction is known as "Dark Frame Subtraction".
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Old Sep 6, 2009, 10:43 AM   #3
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BTW, if they're occurring at shutter speeds faster than 1 second, then the camera should already have them mapped out. Pixels that are always hot (too bright) regardless of camera settings are considered to be "stuck", and remap routines can locate them and update a bad pixel map in EEPROM so that they don't show up in typical shots. If they are occurring at faster shutter speeds (i.e., you have stuck pixels), you can set the date up one month to force an undocumented remap routine.

Basically, these models have an automatic pixel remap algorithm that gets rid of any stuck pixels that would show up in normal exposures on a monthly basis.

If you want to force it, change the date by setting the month forward by one month and save it. When you power your camera off after changing the month with a KM or Sony model, 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).

Then, set your date back to where it's supposed to be again (and some of the KM and Sony models will do a second remap after the next power down since they don't seem to care about how the date was changed, just that the month itself changed).

With some Canon models, using the mirror up sensor clean forces the same type of remap procedure. With many Olympus models, you have a menu choice for it. With some Nikon or other manufacturer's models, you have to send them back to the factory if they develop any that weren't mapped out before the camera shipped (then, they just use service software to locate them and map them out). But, I do have software to do the same thing with some Nikon point and shoot models.

But, if the hot pixels you're seeing with your A200 are only occurring on longer exposures, that's normal (and not what the remap routine is designed to correct by updating a bad pixel table in EEPROM, because you wouldn't want them being mapped out at typical shutter speeds). Removing hot pixels on longer exposures is what the long exposure noise reduction feature is for (so, I'd make sure it's turned on so it can perform a dark frame subtraction on longer exposures).
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Old Sep 6, 2009, 11:40 AM   #4
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I just checked posting history and noticed we've been through this before in July (and now it looks like you're saying you've had the same issue with multiple camera bodies).

That sounds like you're either doing something wrong, or misinterpreting what you're seeing as hot pixels when it's really just normal noise versus pixels bright enough to be considered hot or stuck.

Noise is normal, depending on the ISO speed you're using, aperture/shutter speed being used, subject type, how the image is being exposed, etc. For example, if you're doing something like trying to use higher ISO speeds with a longer exposure, you can expect a lot of pattern noise with almost any camera (for longer exposures, you want to keep your ISO speed set to it's lowest value to keep noise levels down). Just because you see noise, doesn't mean you're seeing hot pixels, depending on their brightness. I suspect that what you're seeing is normal for the photos you're taking and settings being used, and you're just misinterpreting what you are seeing.

So, I'd post a downsized sample image so we can figure out what you're seeing, along with a crop from the image showing some pixels you're referring to (use your mouse to draw a box around a section of it, crop it, and save that crop as a separate image, too.

Make sure the editor you use retains the EXIF information, so that we can see camera settings used.

To post photos here, I'd suggest downsizing using something like the free Irfanview. After opening an image with it (File>Open), look under Image>Resize/Resample. I'd make the longest side around 640 to 800 pixels (and no more than 1024, if you *really* need to show one that large for special purposes), leaving the retain aspect ratio box checked. I normally select the Lanczos algorithm for resizing. Then, when you save the image after resizing (File>Save As), select jpeg as the file type and set the JPEG Quality slider you'll see pop up to around 80%. That will probably get the file size within limits as long as the image is downsized to smaller dimensions first. Make sure to leave the retain EXIF box checked if you want members to see the metadata for camera settings used. Use it to crop a small section from the original (not downsized) showing what you think are hot pixels and attach it to a post here, too.

Then, use the attachment button you'll see when making a post here, which lets you upload images and attach them to a forum post (use the button in the editor tool bar that looks like or , depending on the forum theme you using).
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