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Pixel Mapping
I have an Olympus E-510 and noticed there are a few red pixels in a shot I took with a black background. The menu has an option for pixel mapping but very little is said in the /img/avatar7.jpg's manual about exactly what it does and how it does it. I find that this one area that Olympus needs to work on, when I purchase a high tech gaget I want all the info. I read in a high quality review that I should perform this function every six months to get rid of bad pixels. Can anyone shed more light on the subject.Tim..

Comments (10)

BigScooter wrote:.

I have an Olympus E-510 and noticed there are a few red pixels in ashot I took with a black background. The menu has an option for pixelmapping but very little is said in the owner's manual about exactlywhat it does and how it does it. I find that this one area thatOlympus needs to work on, when I purchase a high tech gaget I wantall the info. I read in a high quality review that I should performthis function every six months to get rid of bad pixels. Can anyoneshed more light on the subject.Tim.

Read page 100 in the owner's manual about "unknown bright dots" to get an explanation, and then page 106 for "pixel mapping".Conrad 'Bye Bye' Birdie'Aspire to inspire before you expire'...

Comment #1

Yes I saw both of those but it doesn't explain what happens to them, are they blacked out instead of red, are they assigned to produce the color nearested to them, or what?Tim..

Comment #2

BigScooter wrote:.

Yes I saw both of those but it doesn't explain what happens to them,are they blacked out instead of red, are they assigned to produce thecolor nearested to them, or what?Tim.

That I can't answer. Sorry. I would assume though if the pixel(s) were dead, they would not produce a color, but they could be interpolating I guess. Just not sure..

Conrad 'Bye Bye' Birdie'Aspire to inspire before you expire'...

Comment #3

Conrad Birdie wrote:.

BigScooter wrote:.

Yes I saw both of those but it doesn't explain what happens to them,are they blacked out instead of red, are they assigned to produce thecolor nearested to them, or what?Tim.

That I can't answer. Sorry. I would assume though if the pixel(s)were dead, they would not produce a color, but they could beinterpolating I guess. Just not sure..

Most people are not interested in things like this. Even some who are interested get confused by the answers..

Go do some research on how a "Bayer sensor" works. You will find out that all the pixels are interpolated. What is hidden for propriatary reasons is exactly how various manufacturers perform these interpolations. Once you understand what Dr. Bayer invented, it's pretty easy to guess how data from bad photosites is "mapped" out of the final result..

Charlie DavisNikon 5700 & Sony R1HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #4

Thanks for the info, not trying to be rude but I thought someone might know, a guess really doesn't answer the question and it's not that important anyhow. I would think they have to grab the properties from the colors in the surrounding pixels otherwise you would have black spots in a white photo if the were just disabled.Tim..

Comment #5

As per usual Chuxter is leading you in the right direction..

The pixels are just interpolated into the appropriate adjacent color and brightness, just as if they weren't there. Ie, they no longer contribute to the interpolation algorhythm. The thought line is a little complicated, I hope that's clear..

The Oly implementation is particularly effective and is what I like to say "non-accumulative". In other words each time you map the sensor it resamples each pixel, even the ones mapped out last time......sometimes they come back to life.A member of the rabble in good standing..

Comment #6

I don't know why I am still writing about this, but I took a photo with the lens cap on. I imported it to LR and I can't see any red pixels but they are in the photo with a black background. The lens photo isn't pure black not even at 1:1 and when I push it to 2:1 or what ever it will let me push it to the screen has groups of pixels all over the place that are from 2 to 4 shades lighter than pure black. I don't know why I find this so interesting, but I just assumed that with no light at ISO 100 with a 1/125 SP that the sensor would not pick anything and maybe that's exacty my problem with that test. The sensor needs the light to give an accurate value to the bad pixels. If anyone bothers to answer this are these spots the same thing as a hot pixel.Tim..

Comment #7

BigScooter wrote:.

Thanks for the info, not trying to be rude but I thought someonemight know, a guess really doesn't answer the question and it's notthat important anyhow. I would think they have to grab the propertiesfrom the colors in the surrounding pixels otherwise you would haveblack spots in a white photo if the were just disabled..

Tim, I wasn't trying to be rude either. My point was that if you want to understand the answer, you have to first understand how Bayer sensors work. You don't...I can tell from your last sentence. The truth is that when your camera (or your computer) de-mosaics the image data from a Bayer sensor, it ALREADY "grabs the properties from the colors in the surrounding photosites (not pixels)". Once you really "get" that, it's an epiphany and the confusion goes away..

Charlie DavisNikon 5700 & Sony R1HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #8

BigScooter wrote:.

I don't know why I am still writing about this, but I took a photowith the lens cap on. I imported it to LR and I can't see any redpixels but they are in the photo with a black background. The lensphoto isn't pure black not even at 1:1 and when I push it to 2:1 orwhat ever it will let me push it to the screen has groups of pixelsall over the place that are from 2 to 4 shades lighter than pureblack. I don't know why I find this so interesting, but I justassumed that with no light at ISO 100 with a 1/125 SP that the sensorwould not pick anything and maybe that's exacty my problem with thattest. The sensor needs the light to give an accurate value to the badpixels. If anyone bothers to answer this are these spots the samething as a hot pixel..

If by "from 2 to 4 shades lighter than pure black" you mean they have values of about 003, then these are "warm" pixels. A "hot" pixel is about 20X that value..

There will ALWAYS be small variations in the sensitivity of individual photosites. As the exposure time and sensitivity (ISO) increases, the camera will probably switch to an automatic NR mode, where it takes two frames (one will be a black frame) and subtracts them. This will eliminate or at least reduce the strength of the dark noise. I'm not intimate with the E-510, but most cameras do this nowadays. It's called "dark frame subtraction"....

You might be interested in this utility...a "dead pixel test":.

Http://www.starzen.com/...aging/Utilities/DeadPixelTest/tabid/98/Default.aspx.

Charlie DavisNikon 5700 & Sony R1HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #9

Thanks, I read the Word document about how to test. E-510's do not support Tiff but I guess I'll try a Raw or Uncompressed JPEG..

Thanks againTim..

Comment #10

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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