Go Back   Steve's Digicams Forums > Digital SLR and Interchangeable Lens Cameras > Canon EOS dSLR

Reply
 
Thread Tools Search this Thread
Old Jun 25, 2009, 4:29 AM   #11
Super Moderator
 
Mark1616's Avatar
 
Join Date: Oct 2005
Posts: 7,452
Default

Nope it is still there which is a pain however it isn't showing up in normal photos so if I shoot somewhere dark I can easily remove it in a couple of seconds, I'm trying to work out how I want to handle it, I might send it into Canon after the next wedding shoot to get it sorted but we shall see.
Mark1616 is offline   Reply With Quote
Old Jun 25, 2009, 10:29 AM   #12
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

If it's not showing up in Normal photos, that's probably why any built in remap function isn't working (assuming that the camera has one, as you sometimes see reported with Canon models by locking up the mirror using their sensor cleaning mode).

Auto Remap functions are going to have a brightness threshold a pixel showing up with a "dark frame" exposure must meet before it's added to the camera's bad pixel map in EEPROM.

Basically, a typical remap routine is taking a dark frame exposure and looking for any bright pixels (since those are the only ones that should show up). Once they meet a certain brightness threshold, they're added to a bad pixel table in EEPROM (so that the camera replaces them with values from adjacent pixels).

But, the remap routines may not always map out all visible pixels from a dark frame (since if they're too dim to show up typical photos, you don't want the camera mapping out any more pixels than necessary). Any that do show up are typically going to be brighter on longer exposures.

But, most modern camera have a built in dark frame subtraction noise system that can map out hot pixels that only show up in long exposures (1 second or longer), so that they don't have to leave them mapped out for typical photos. With Canon models, you can turn this feature on or off via a custom setting (so that they're mapped out on exposures of 1 second or longer).

If you want to see how bright they are, try this software (and you may have to lower the default threshold for dimmer ones to show up in the list).

http://www.starzen.com/imaging/deadpixeltest.htm

Here's an old thread discussing the issue (and you'll also see a link to Tabaware's pixelzap software designed to detect and remove them in PP):

http://forums.steves-digicams.com/so...tml#post571070
JimC is offline   Reply With Quote
Old Jun 25, 2009, 10:47 AM   #13
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

P.S.

If it were mine, I'd probably try increasing the ISO speed and see if it uses the faster speed for remapping, too (chances are, any stuck pixels are going to be hotter at higher ISO speeds), trying both the sensor cleaning mode and moving the date up (in case the camera has more than one undocumented way to call the remap function).

Making sure the sensor is as warm as possible (as someone else suggested) is probably a good idea, too. Noise levels (as well as the brightness of any "borderline" stuck pixels) will probably increase with sensor temperature, making it more likely that your pixel will meet the brightness threshold a remap function is looking for before adding it to the bad pixel table in EEPROM.
JimC is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 12:30 AM.