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

Reply
 
Thread Tools Search this Thread
Old Jun 28, 2006, 11:42 PM   #1
Senior Member
 
Justin Hancock's Avatar
 
Join Date: Mar 2006
Posts: 272
Default

I've just noticed something in the images being recorded on my Canon Rebel XT (with 18-55mm kit lense). Below is a cropped portion of an image:



And below is it magnified to about 200%:



Any ideas what it could be? It doesn't look like any dust speck I've seen before. Perhaps something may be wrong with the sensor? The camera is almost brand new...probably 3 or 4 months old and I treat it with the utmost of care.
Justin Hancock is offline   Reply With Quote
Sponsored Links
Old Jun 29, 2006, 1:49 AM   #2
Super Moderator
 
peripatetic's Avatar
 
Join Date: Nov 2004
Posts: 3,599
Default

I think that's a dead pixel.

I'm not sure if the XT has a pixel-remapping feature, if not then you need to take it back to Canon for remapping or replacement.
peripatetic is offline   Reply With Quote
Old Jun 29, 2006, 2:52 AM   #3
Member
 
Broncosaurus's Avatar
 
Join Date: Jun 2006
Posts: 37
Default

I have a pic with an X just like that, taken with a Sony PnS. It only occured on one shot so I'm not worrying about it, 'specially since I'm now using a Rebel xt. Oddly, when zooming in on this X in Photoshop, it doesn't enlarge with the rest of the shot. Its size on the screen remains constant.
Broncosaurus is offline   Reply With Quote
Old Jun 29, 2006, 5:41 AM   #4
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,545
Default

IMO it may not be a dead pixel...
1. Look at it size relative to the letterings close by
2. A pixel only comes in Red, Green or Blue so after the demosaic they always get "re-mapped"

-> It has to be a whole group of pixels (pretty much a damage sensor), or a bad computation if this does happen every time - check the RAW output

Did you clean the sensor lately? The X star shape is intriguing and nearer to the sensor plane than a dust spot (from a tiny ding on the IR filter)
NHL is offline   Reply With Quote
Old Jun 29, 2006, 3:14 PM   #5
Senior Member
 
pj1974's Avatar
 
Join Date: Jun 2005
Location: Adelaide, South Australia
Posts: 2,914
Default

Hi Justin,

I have a 350D (Rebel XT) and for a few weeks I also had this "X mark", mainly noticable in dark / long exposure settings (in brighter light it WAS still there but hardly visible). So I was quite convinced it was a dead pixel (or group of pixels). It didn't happen in the beginning... about 3 weeks or 1000 shots after I got the camera.

But then it (mysteriously) disappeared! (which made me happy!) My night time shots don't show up anything of this mysterious elusive "X" anymore! It was visible using both my lenses (18-55 and 28-135 which I was using then, and still use now). But now it's definitely gone. I hope it doesn't come back.

As for you, I hope it will disappear too (sometime soon!) forever!!! :O

As peripatetic says, if the XT has a pixel-remapping feature maybe that will remove it. I'm not sure if that happened to mine...

Interesting NHL says that dead pixels only come in the 3 primary colours (and he is a guy who always seems to know what he's talking about).... but mine was definitely NOT green, red or blue, but a lighter shade (almost white, like yours was) but it seemed to be slightly affected by whatever was the colour of the pixels around it (when I really zoomed in I could see this). But that's pixel peeping, right?! :-)

Anyway, let us know how you go! Best of luck!

Paul
pj1974 is offline   Reply With Quote
Old Jun 29, 2006, 4:09 PM   #6
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,545
Default

pj1974 wrote:
Quote:
Interesting NHL says that dead pixels only come in the 3 primary colours (and he is a guy who always seems to know what he's talking about).... but mine was definitely NOT green, red or blue, but a lighter shade (almost white, like yours was)
Actually I lied...
They can come in different color too but never white: http://www.dpreview.com/learn/?/Glos...r_array_01.htm
-> White is only the interpolation results of the primary colors

Only the Foveon sensor can see all three colors per pixels, but this is a Canon camera :idea:

This is why I hinted at the computational error - Overflow can happen in camera too since it's just another computer. The key here is the X shaped, since it happened to many people it could come from the X-files... :lol: :-) :G
NHL is offline   Reply With Quote
Old Jun 29, 2006, 4:19 PM   #7
Member
 
Join Date: Feb 2005
Posts: 51
Default

Actually if I'm not mistaken, it's a "hot" pixel. What this means is that the pixel is constantly in the"on" position. I bet if you'd shoot something bright, it would not be noticeable. That's why you notice it during long exposures and dark photos. The reason it's a star shape is that the pixel "bleeds" onto the adjecent pixels and thus making them overexpose slightly as well.



TT
TTfoto is offline   Reply With Quote
Old Jun 29, 2006, 7:15 PM   #8
Senior Member
 
hgernhardtjr's Avatar
 
Join Date: Nov 2004
Posts: 516
Default

I agree with TTfoto ... it is a classic "hot pixel". Do a Google search and you will find much info. Read this simple explination http://www.imaging-resource.com/ARTS/HOT/HOT.HTM
hgernhardtjr is offline   Reply With Quote
Old Jun 29, 2006, 9:25 PM   #9
Senior Member
 
Justin Hancock's Avatar
 
Join Date: Mar 2006
Posts: 272
Default

I called Canon regarding the issue and the support tech said that it does sound like a hot pixel; I was offered to send it in for repair but I believe what I'll do is wait until my warranty is about up before sending it in - in case I have any other issues so I can get them all fixed at the same time.

I have some events coming up that I need my camera for.

Thanks for the help guys
Justin Hancock is offline   Reply With Quote
Old Jun 30, 2006, 8:41 AM   #10
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,545
Default

IMO - That's not a "hot pixel"

1. It's too big, check @ its size against the neighbouring letters
2. It has a geometrical shape round first with a "thin" Philips type of screw head
(A grouping of whole bunch may be)

This is what a "hot pixel" looks like:

Attached Images
 
NHL 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 2:03 AM.