Pictures taken with my 1D Mark IV show a blue horizontal line at the bottom from ISO 400 onwards.

[numenius]

Pictures taken with my 1D Mark IV show a blue horizontal line at the bottom from ISO 400 onwards. So far nobody has been able tot tell me the cause of this problem. The body is still quite new (15000 pics taken).

[numenius]

https://www.dropbox.com/s/4onjchalabddhx0/CX7P2709.CR2

This time it should work!

[rfdesigner]

Here is what the end of the blue line looks like on the RAW image.  (it's a grey chequerboard as colour in a bayer matrix image is implicit by pixel location..   and this hasn't yet been 'interpreted')

https://www.dropbox.com/s/ahzuir3tuwis94d/blue_line.bmp

What we can see is the end of the line, and some 'slices' of both the dark and light lines, and a normal slice..  all slices are of the end of the lines, so the little graphs show a 'normal' segment on their leftmost edge, they are showing intensity vs position across the vertical branch in the image.

What these are telling us is that two rows are affected, one is overly dark and one overly light. this looks like a failure at one pixel location (the end of the line) damaging the entire row.  You should be able to see in the middle and bottom graphs that there is still real signal in both the dark and the light rows, so the right software and some reference flat-light and dark images might well correct for it...   alternatively the entire row can be scrapped and replaced with an average of the row above and below.

It's also safe to say your sensor isn't going to get better, but neither is it about to completly die on you..   my astro camera which is much more delicate as it's CCD has a couple of slightly 'hot' columns and I can process them out entirely.

I hope this is of some use.  (I tried processing out the column in IRIS but haven't found a sufficiently good way as yet.)

Derek

edit:  this of any use?..  (need a MAC)  http://people.csail.mit.edu/ericchan/tmp/FixBadPixels.pdf

[numenius]

Your answer certainly is of some use. Thanks for all your trouble and time you put into it. Next step will be to find the right  software. I'll begin with pixelfixer.

[ebiggs1]

Try a different CF or SD card. Card may have gone south on you.

[TCampbell]

I agree that it looks like a column of photosites is not working.  But... I'm curious as to why this would only happen at ISO 400 or above. 

The sensor is covered with photosites -- they are monochrome.   On top of the photosites is the "bayer mask".  The mask is a checkboard pattern of red, green, and blue "lenses" which makes the photosite beneath only sensitive to that particular color.  They are group in clusters of 4 photosites in a 2x2 matrix.  Two of the four squares (in opposing corners) are green.  One corner is red.  One corner is blue.  If you were to lose a column which happens to be along the red/green column (as opposed to the green/blue) then you'd lose red sensitive and half the green sensitivity in that column.  The result would be that this column is flanked by two "working" columns which are full of green/blue photosites... hence the teal blue look.

I do not know if this will work for you, but oddly... you can actually sometimes "clear" stuck pixels (but usually this is an indvidiual stuck pixel... not a whole column of them) by putting the camera into manual sensor cleaning mode (and you may have to do this 2 or three times).  While the normal point of the self-cleaning mode is to flip up the reflex mirror and open the shutter so that you can inspect and clean the sensor (really the front-most filter because you can't actually touch the real sensor), it also neutralizes the charge on the sensor (or so I've read).  This charging and discharging of the sensor a few times can often get "stuck" pixels to start working again.  BUT AGAIN... I've only ever seen this used on individual stuck pixels... never a whole row.

[rfdesigner]

I really want to know if we have additional false signal, missing signal, or cross contaminated signal between two rows.

The ISO 400 and above could come from different bias for high ISO..  The ratio of well depth to readout noise on these sensors is sufficiently high that I would not be at all suprised to see additional in pixel gain added as an option, either by additional circuitry or by adjusting bias to improve gain.

If the damage is rock solid, it is possible that the OP could process around it..  but it would be a pain to have to do that, I don't know if the long shot dark subtraction algorithum would help.  The 5D has the High ISO multi-shot noise reduction algoritum.. if the 1DIV has that too it could help so long as the damage is just adding an offset to the affected pixels.

The idea of a highly charged spek of dust contaminating things is possible and worth doing sensor cleaning for, I'll remember that one.

[diverhank]

Have you tried turning on/off the high ISO filter and see if it makes a difference. The fact it only shows up at higher ISO shows that it's an ISO artifact, not a sensor problem. Anyway, just a guess on my part.

[diverhank]

If the line is not removed by turning off the high ISO filtering then there's not much you can do at this point. This kind of line, I think, is caused by a few hot pixels in the sensor but is made into a straight line by camera processing and it will show up in the RAW file.
There is a freeware out there called Pixel Fixer that you can use to get rid of the line. The beauty is you can specify the ISO range to do the processing.
http://www.pixelfixer.org/


I haven't tried the above program or this one idea I have because luckily I don't have this problem...the 1DMk4, as with many others if not all, has the ability for you to map out the dirt...even though at this magnification it's hard to tell the offending pixels (brighter, larger than the rest), you might want to map them out. This alone might get rid of the entire line...it's worth a try.

Best of luck and sorry for your trouble.