Hot pixel issue - E-PL5 JPEG only

Discussion in 'Olympus Cameras' started by Ccasey, Nov 1, 2013.

  1. Ccasey

    Ccasey Mu-43 Regular

    157
    Jul 29, 2011
    Austin, TX
    Chris
    Hi,

    I'm fairly new to m4/3 and very new to Olympus cameras. I ordered a refurb E-PL5 and noticed a single red pixel in the middle of some of my shots from the first day. It wasn't in every shot, but it was present in more than just one image. These are not high ISO images - the crops below were taken from a shot @ ISO 320. Oddly, the red pixel appears only in the JPEG file - the corresponding RAW file does not have the same issue:

    crop from JPEG (I believe I was still shooting with the Natural profile):
    [​IMG]

    same crop from unprocessed RAW file (LR 4.4 export):
    [​IMG]

    I did see mention of "Pixel Mapping" in a search, but I'm most interested/concerned about why I'm seeing this only in the JPEG and not the RAW file. I would've thought that Pixel Mapping would affect the RAW data. After reading here (http://www.olympusamerica.com/crm/oneoffpages/ask_oly/crm_e_ask_oly_03_09.asp), I'm not sure it's the same thing, anyway, because my aberration is neither white nor black.

    Has anyone run into this before? As I tend to shoot RAW it's not really a big deal, and even with a JPEG it's easy to fix.

    Thanks in advance,
    Chris
     
  2. madmaxmedia

    madmaxmedia Mu-43 Veteran

    335
    Feb 20, 2010
    Lightroom may be automatically removing the hot pixel from your RAW files- that is, the red pixel may actually be in the RAW file.

    I would just do the pixel mapping, which will probably remove it altogether regardless of format.
     
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  3. Ccasey

    Ccasey Mu-43 Regular

    157
    Jul 29, 2011
    Austin, TX
    Chris
    Thanks for the reply - it seems odd that it would be stored in the RAW data and -not- corrected in the JPEG from the camera, but it does seem like it wouldn't hurt to do the mapping.

    I'll reply back if it continues after the mapping.

    -Chris
     
  4. Replytoken

    Replytoken Mu-43 Hall of Famer

    May 7, 2012
    Puget Sound
    Ken
    Chris,

    I am having the same issue with another brand camera. I also asked about this behavior, and have been told by several folks that the reason that you do not see the pixel in the raw file is that, like madmaxmedia said, most programs that can read raw files usually automatically map out the bad pixel.

    --Ken
     
  5. rbelyell

    rbelyell Mu-43 Veteran

    356
    Sep 15, 2013
    Mountains of NY
    sorry for the stupid question, esp given ive been photographing for well over 20 years. what is pixel mapping and how does it work? i too have an epl 5 with a 'blank' pixel id like to get rid of...
     
  6. Ccasey

    Ccasey Mu-43 Regular

    157
    Jul 29, 2011
    Austin, TX
    Chris
    Ken,

    Thanks for the reply. I'm still mystified by the appearance of the hot pixel in the JPG, but I returned the EPL-5 (Olympus refurb) so I'm no longer directly affected. I do appreciate the explanation, though, and the confirmation from you. Will file it away for future use.

    Tony,

    Not a stupid question IMO. The way I understand it, pixel mapping is a means of the camera running a self-check on the image sensor and detecting any pixels that are not responding as expected. Once the pixels are identified, the processing engine can use the surrounding pixels to approximate a "good" value for the non-responsive pixel. It's a loss of real data, but the loss is so minute that a good substitution should be undetectable.

    Thanks!
     
  7. Replytoken

    Replytoken Mu-43 Hall of Famer

    May 7, 2012
    Puget Sound
    Ken
    Not really a stupid question in my book. The simple, not-technical, answer is that problem pixels are identified ("mapped") on the sensor, and the processor then usually replaces their value with that of an adjacent pixel in your image file so that they better blend in with thier adjacent pixels. It does not actually change the state of the pixel in question, it just masks its bad output. This used to be done by factory technicians, but many companies, like Olympus, decided to offer the ability to address this problem to its users. I wish more companies would also offer it on their cameras. It saves a lot of hassle if you do not want to deal with the problem in post processing. I am sure there is a more technical answer, but this should give you an idea of the process.

    --Ken
     
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  8. dhazeghi

    dhazeghi Mu-43 Hall of Famer

    Aug 6, 2010
    San Jose, CA
    Dara
    It's worth noting that hot pixels are not uncommon, especially with mirrorless cameras, where the sensor is essentially being read continuously when the camera is power up. The camera's JPEG engine isn't particularly clever, so it doesn't fix the hot pixel in the output. Lightroom's processing is considerably more sophisticated. Pixel mapping is good for genuinely stuck hot pixels (those that are always on) but many hot pixels simply come and go as the sensor warms up and cools down over use. The only case where hot pixels would concern me is if you have a cluster of stuck pixels in one area - that's a case where getting the camera exchanged might be a good idea.
     
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  9. rbelyell

    rbelyell Mu-43 Veteran

    356
    Sep 15, 2013
    Mountains of NY
    thanks ken. so the process for fixing it is--what? going in the menu system, finding the 'pixel mapping' feature and simply 'activating' it, or is there something more to it?
     
  10. HarryS

    HarryS Mu-43 Top Veteran

    921
    Jun 23, 2012
    Midwest, USA
    On an EPL5, pixel mapping is the first selection in the Menu>Gear-J page.

    Start it and you see the shutter close momentarily to shut off light. I would presume it now reads the sensor, and any pixel that is not dark is assumed to be stuck and its location put into a table. This doesn't take long, maybe 5 seconds. Later, when you take a real picture, the table is consulted and any stuck pixels are replaced with the average data from its neighbors.

    I've looked once on my PEN for stuck pixdls. Found one, and the mapping got rid of it.
     
  11. Replytoken

    Replytoken Mu-43 Hall of Famer

    May 7, 2012
    Puget Sound
    Ken
    On Olympus camera that have pixel mapping, yes. Then take a look and see if the problem has been resolved. On cameras that do not offer pixel mapping, you can either send it in for repair (i.e. pixel mapping), correct the problem in post processing (assuming you post process), or learn to live with the problem.

    --Ken
     
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  12. monk3y

    monk3y Mu-43 Hall of Famer

    May 14, 2013
    in The Cloud...
    Steven
    Yes this is the fix for most Olympus cameras. I also freaked out when I had the E-P5 before... a quick pixel mapping solved the issue.
     
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  13. rbelyell

    rbelyell Mu-43 Veteran

    356
    Sep 15, 2013
    Mountains of NY
    cool! thank you guys!
     
  14. DynaSport

    DynaSport Mu-43 All-Pro

    Jan 5, 2013
    Dan
    Had to pixel map my E-PM1 a while back. The folks on this forum guided me through it as well. That is one the things I love most about this forum.
     
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