Pixel Mapping on E-500?

[cyuxiang]

Are there any advantages/disadvantages to this feature? Should it be done on a scheduled basis (like once a year), or only when hot/stuck pixels appear? Thanks.

[Kid Shotter]

Pixel mapping should only be done when hot pixel appear.Also,do a few 30 second expourse(Heat the sensor up) then do pixel mapping,

[nikkie]

how is this done?
pls illustrate.
kum sia.

[drakon09]

Just to clarify on pixel mapping.

What it does is reset "dead" pixels. These dead pixels show up as solid red, green or blue spots on your pictures. Do not mistake long exposure noise for dead pixels; long exposure noise is randomly scattered all over. Dead pixels show up at the same spot on every picture.

It is a very useful function; on cameras without pixel mapping you need to send it back to the service centre to reset dead pixels.

[cyuxiang]

Yup drakon09, I understand the long exposure noise & how it can be cleared up using the "noise reduction" feature which compares two simultaneous exposures & eliminates the noise.

Anyways I've read somewhere that once pixel mapping is done, the information cannot be undone, even with hard reset. So does that mean that when buying 2nd-hand cameras there's no way to check for any hot pixels on the sensor? Another question is that should the existence of hot pixels be a criteria in choosing 2nd-hand camera in the first place?

[drakon09]

Originally Posted by cyuxiang Yup drakon09, I understand the long exposure noise & how it can be cleared up using the "noise reduction" feature which compares two simultaneous exposures & eliminates the noise. Anyways I've read somewhere that once pixel mapping is done, the information cannot be undone, even with hard reset. So does that mean that when buying 2nd-hand cameras there's no way to check for any hot pixels on the sensor? Another question is that should the existence of hot pixels be a criteria in choosing 2nd-hand camera in the first place?

It is easy to check for hot pixels; snap with the lens cap on. The hot pixel will show up against the black. All Oly cams come with built-in pixel mapping function so it really isn't much on issue. On cams without the function it means a trip down to the service centre, unless you can live with cloning the spot out of every photo taken.

Pixel mapping is a very simple process, think of it as rebooting the sensor, so it really does not damage the sensor in any way.

Personally, if I do have an important shoot to do, I'll just pixel map first just in case pixels do get stuck; on one occasion I had to clone out the hot spot for 300 photos.

Not fun.

[cyuxiang]

Originally Posted by drakon09 It is easy to check for hot pixels; snap with the lens cap on. The hot pixel will show up against the black. All Oly cams come with built-in pixel mapping function so it really isn't much on issue. On cams without the function it means a trip down to the service centre, unless you can live with cloning the spot out of every photo taken. Pixel mapping is a very simple process, think of it as rebooting the sensor, so it really does not damage the sensor in any way. Personally, if I do have an important shoot to do, I'll just pixel map first just in case pixels do get stuck; on one occasion I had to clone out the hot spot for 300 photos. Not fun.

Hey I found this utility, going to give it a try now: http://www.starzen.com/imaging/deadpixeltest.htm

Scanning the whole full-res picture for a hot pixel using the naked eye can be quite a strain

edit: Tried the program. It supports .jpeg/.tiff/.orf, but it doesn't recognise the .orf files from my E500. Took a few shots in .tiff, tested my camera to have no hot pixels to a relatively low threshold. It also provide the pixel co-ordinates for suspected hot pixels so can double-check in Photoshop.

[holidaydom]

I think we need some kind of clarification here...

Dead Pixels: Ones that appear BLACK regardless of exposure
Stuck Pixels: Ones that appear Red/Blue/Green regardless of exposure
Noise: Red/Blue/Green/White pixels that increase with exposure time

My understand is that Pixel Mapping maps out the dead and stuck pixels that are invetiable in the imager (CCD Chip) fabrication process.

What pixel mapping does is detect these dead and stuck pixels and replace their value with the average of thir nearest neighbours.

Noise is not removed or reduced by pixel mapping but rather via the NR function that kicks in when activated and for exposures longer than 2 seconds.

Pixel mapping gives the "impression" of improving/reducing noise because it removes stuck pixels.

From what I've noticed in my pictures, noise is generally random but if I take several frames at long exposures, I will notice that the noisy pixels usually appear in the same place for all the frames taken...

Someone please correct me if I wrong so as not to mislead the good ppl in this forum

Kudos~!!

[Clockunder]

Originally Posted by holidaydom I think we need some kind of clarification here... Dead Pixels: Ones that appear BLACK regardless of exposure Stuck Pixels: Ones that appear Red/Blue/Green regardless of exposure Noise: Red/Blue/Green/White pixels that increase with exposure time My understand is that Pixel Mapping maps out the dead and stuck pixels that are invetiable in the imager (CCD Chip) fabrication process. What pixel mapping does is detect these dead and stuck pixels and replace their value with the average of thir nearest neighbours. Noise is not removed or reduced by pixel mapping but rather via the NR function that kicks in when activated and for exposures longer than 2 seconds. Pixel mapping gives the "impression" of improving/reducing noise because it removes stuck pixels. From what I've noticed in my pictures, noise is generally random but if I take several frames at long exposures, I will notice that the noisy pixels usually appear in the same place for all the frames taken... Someone please correct me if I wrong so as not to mislead the good ppl in this forum Kudos~!!

Yes, Dead (black) and Stuck (bright) pixels are removed algorithmically with the use of some kind of averaging of neighbouring pixels to estimate the light for the particular dead/stuck pixel in question. Once a pixel is physically dead or stuck, it remains that way. Pixel mapping is a software thing to identify dead/stuck pixel and then ear-mark them. It's not a hardware reset. Once pixel mapping is done, the camera will in the future ignore those ear-marked pixels value in picture taking and always calculate their values instead for processing.

Noise caused by hot pixels is a separated issue from dead/stuck pixels and is caused by long exposure (heat) and is removed by NR function which takes another image with shutter closed to determine which pixels remain bright even with the shutter closed and then replace those pixel values (probably with averages of neighbouring pixels).

The main difference between dead/stuck pixels and Hot pixels is that the former occurs regardless of exposure time while the latter only become as such if the exposure is long (more than a couple of seconds).

So for pixel mapping, there is no need to heat up the camera first by taking a few long exposure shots. It is available as a function in the menu on some cameras. Read your camera manual. For others, it can only be done by sending it back to the service centre.

(p.s. in any case, all the pixels that we see in the final image are all calculated averages from the light value collected on neighbouring RGB physical pixels for the Bayer type image sensor or on different layers on Foveon type image sensor).

[cyuxiang]

One way to differentiate between noise & hot pixels would then be to compare multiple shots? If the abnormal pixels are consistently within the same area then it would be hot pixels.

One more thing: Pixel mapping algorithm doesn't affect RAWs right?

[drakon09]

Nope.