Go Back   Steve's Digicams Forums > Digicam Help > General Discussion

Reply
 
Thread Tools Search this Thread
Old Oct 5, 2010, 3:06 PM   #1
Senior Member
 
Ordo's Avatar
 
Join Date: Jul 2009
Location: BsAs
Posts: 3,452
Default Lost pixels

Virgin of Itati. The jpg file shows lots of artifacts and loss of detail. I post it just as a reference.



Here's the tif 51 Mb file:

http://www.megaupload.com/?d=Y3RBVT5K

When i uber crop to show details i find some lost pixels (white):



Is it normal to find lost pixels? Pick is a quick hand held pick. Eos 7D.
Ordo is offline   Reply With Quote
Sponsored Links
Old Oct 5, 2010, 3:25 PM   #2
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,572
Default

Some could be noise, and some could be oversharpening artifacts that will apear in almost any image when pixel peeping.
__________________
  • The lens is the thing.
  • 'Full Frame' is the new 'Medium Format'.
  • "One good test is worth a thousand expert opinions." - Tex Johnston, Boeing 707 test pilot.
TCav is offline   Reply With Quote
Old Oct 5, 2010, 3:31 PM   #3
Senior Member
 
Ordo's Avatar
 
Join Date: Jul 2009
Location: BsAs
Posts: 3,452
Default

So it's not a sensor issue. Could it also be the 3200 ISO? Should I expect less lost pixels with a lower ISO?
Ordo is offline   Reply With Quote
Old Oct 5, 2010, 5:51 PM   #4
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,572
Default

Quote:
Originally Posted by Ordo View Post
... Could it also be the 3200 ISO? Should I expect less lost pixels with a lower ISO?
You shot this at ISO 3200, 1/125 and f/8, with a focal length of 31mm on a Canon 7D. You could had used a shutter speed of 1/60 and used an ISO of 1600. Further, you could have used an aperture of f/5.6 and used an ISO of 800. You could possibly even used an aperture of f/4.0 and gotten away with an ISO of 400. If you were using a stabilized lens, you could probably even gotten away with a shutter speed of 1/30 and used an ISO of 200.

Cranking up the ISO shoudl really be the least thing you do when selecting exposure settings.
__________________
  • The lens is the thing.
  • 'Full Frame' is the new 'Medium Format'.
  • "One good test is worth a thousand expert opinions." - Tex Johnston, Boeing 707 test pilot.
TCav is offline   Reply With Quote
Old Oct 5, 2010, 6:01 PM   #5
Senior Member
 
MartinSykes's Avatar
 
Join Date: Feb 2010
Location: Cheshire, UK
Posts: 854
Default

Quote:
Originally Posted by Ordo View Post
So it's not a sensor issue. Could it also be the 3200 ISO? Should I expect less lost pixels with a lower ISO?
Try taking another photo and see if the same pixels are missing each time.
__________________
AutoHDR - Free HDR software for Windows at http://www.autohdr.co.uk on Facebook at http://www.facebook.com/home.php?sk=...36045126467361
My Flickr stream: http://www.flickr.com/photos/martinsykes
Panasonic DMC-FZ38, Sony ­α580
MartinSykes is offline   Reply With Quote
Old Oct 5, 2010, 6:16 PM   #6
Senior Member
 
Ordo's Avatar
 
Join Date: Jul 2009
Location: BsAs
Posts: 3,452
Default

Yes, i know i'm pushing the camera... I'll try tomorrow with a tripod and low ISO. Even more: i will measure incident light (oh, the good old times) and get some EV bracketing also.
But fooling around with zoomed in unsharp mask i can see how it literally "kills" pixels.
Thanks and thanks again.
Ordo is offline   Reply With Quote
Old Oct 5, 2010, 6:23 PM   #7
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,572
Default

"Sharpening" doesn't actually sharpen anything. It just increases the contrast between light areas and adjacent dark areas (and vice versa), by lightening light pixels near the dark areas and darkening dark pixels near the light areas. This accentuates the borders, making the difference more apparent, but it does this by manipulating the colors.
__________________
  • The lens is the thing.
  • 'Full Frame' is the new 'Medium Format'.
  • "One good test is worth a thousand expert opinions." - Tex Johnston, Boeing 707 test pilot.

Last edited by TCav; Oct 5, 2010 at 7:58 PM. Reason: sp
TCav is offline   Reply With Quote
Old Oct 5, 2010, 7:34 PM   #8
Senior Member
 
Ordo's Avatar
 
Join Date: Jul 2009
Location: BsAs
Posts: 3,452
Default

What does Contrast do to the pick? Is there kind of an overlap with USMask?
Ordo is offline   Reply With Quote
Old Oct 5, 2010, 7:57 PM   #9
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,572
Default

"Contrast" lightens the light colors throughout the image, and darkens the dark colors.
__________________
  • The lens is the thing.
  • 'Full Frame' is the new 'Medium Format'.
  • "One good test is worth a thousand expert opinions." - Tex Johnston, Boeing 707 test pilot.
TCav is offline   Reply With Quote
Old Oct 5, 2010, 7:57 PM   #10
Senior Member
 
VTphotog's Avatar
 
Join Date: Mar 2005
Location: Extreme Northeastern Vermont, USA
Posts: 4,234
Default

Contrast adjustment affects the entire photo. If you make an adjustment and look at the before and after histogram, you will see the difference.
Unsharp mask selects a small area, which you determine by setting the radius, and changes the contrast locally. (but it does this over the entire photo, one small area at a time) For sharpening, the area chosen is small - maybe less than a pixel- and the amount of adjustment is relatively large. You can also use it for local contrast enhancement by selecting a larger radius, depending on the overall size of the photo (maybe 10 to 30 pixels) and using a smaller amount.
The sharpening tools use edge enhancement by determining where edges occur, and increasing contrast for a couple pixels surrounding the edge. Unsharp mask works everywhere in the photo.
Using high ISO settings increases noise, and when you sharpen, the difference in the noisy pixels becomes more apparent. Noise reduction, either in the camera, or post-process, will often leave some of the noisy pixels behind, and sharpening then brings them out. This is what looks like happened with your crop.

brian
VTphotog 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 5:08 AM.