De-activated pixels

[Robert Roaldi]

I am no expert so I am speaking purely as a consumer. On a new camera, I expect all the pixels to be working. If they aren't or even if they don't guarantee it, I would be upset, and if I knew beforehand I would likely not buy the camera.

This raises a question about buying 2nd hand digital cameras, which will become more and more of an issue. It's one more thing to check for. The question arises about how or whether bad pixels are "fixed". Do they exchange the sensor? Do they mask the bad pixels using interpolation algorithms the way bad blocks on a hard disk are mapped out of usage? How DOES one check for this?

Theoretically, I could own a few bad pixels and never know it. One could then say that if I didn't notice then it's not a problem, something with which I would not agree, BTW. Whether I notice or not, I am not getting what I thought I was paying for.

If bad pixels are "masked" out in this manner, it would seem to me that the industry and equipment reviewers should be making this clear to the user community. If I knew that camera A fixes this problem by "masking" a pixel out of usage, while camera B does NOT, it affects which one I may choose to buy. But I can't say that I have seen this issue mentioned very much. Whether it's because it's a non-issue or not, I don't know. I hope that electonics experts can shed some light on this.

[dpw]

I guess it's a matter of acceptability. If the camera has a defect now, what happens when the guarantee expires and more pixels go?

Would you be pissed if you'd just got a Canon 1Ds, and found a bad pixel - having spent all that money?

I understand that there is some not generally available tech specification on the number of duff pixels per million that is acceptable.

I shall ring Canon on Monday for a chat, with a view to taking the camera back for a replacement. I'll let you know what they say.

Regards

Dan

[Stefan Pop Lazic]

This is not acceptable at all. Go and change your camera.

[dpw]

As a follow up...

I took my Pro1 back to the reatailer and asked for a replacement - which they were more than happy to do.

However, the new camera also has a dead pixel!

I spoke to Canon UK tech support today to ask what they thought. They informed me that on a new camera, all CCD pixels should work. On LCD screens they have a tolerance of 0.01% total pixel number. On CCD, they expect 100%.

Back I go again!

[dpw]

Funny enough - or perhaps not so funny, but the third camera also has dead pixels (in this case two). Thankfully I found these in the store negating another round trip.

They didn't have anymore Pro1s in stock therefore i've got my money back and am now looking again!

Shame really, as it does appear to be quite a nice camera.

[Robert Roaldi]

Three bad cameras, what a nuisance.

Out of curiosity how did you find the dead pixels in the store? Eyeballing the LCD display?

[crspe]

It is actually completely normal for a sensor to have bad pixels and this is already publicly acknowledged by the manufacturers.  Here is a quote from Chuck Westfall (of Canon, found  
here):

I addressed the pixel mapping issue here about a month ago in message #140805. Here's the relevant excerpt:

What we are referring to here as "pixel mapping" is a diagnostic software program used by the Canon Factory Service Center to identify dead pixels in an imager and essentially replace their data with good information from adjacent "live" pixels. There's nothing new or unusual or exclusive to Canon about this procedure. Virtually all imagers used in digital cameras today have some degree of dead pixels present when they are manufactured. Mapping out the dead pixels is something that occurs initially at the factory when the camera is assembled as a part of the quality checking procedure. However, even though all dead pixels present at the time of camera assembly are mapped out at the factory, more can appear at a later date for a variety of reasons. When this happens, the Service Dept. can step in and remedy the problem. This service is typically offered at no charge while the camera is in warranty.

--------------------
Chuck Westfall
Director/Technical Information Dept.
Camera Division/Canon U.S.A., Inc.

I hope this clears it up for you all - so, if you have a bad pixel on a camera and it is really annoying you, then Canon will typically fix it cost free under warranty.  Of course to have an automatic action to fix it in Photoshop will take almost no time to set up and can be run in batch mode.

[dpw]

Just a quick question for you...

Is it acceptable to have a deactivated pixel on the CCD of a new camera?

Background - I've just purchased a Canon Powershot Pro 1, and can see at leat one "white spot" (all be it small) on the image.

Is it being unreasonable to think that all 8 million pixels will work?

Comments appreciated!

Regards

Daniel.

[Howard Smith]

I'm no expert either, but it seems to me that 1 failure in 8 million tries isn't too bad.  Even if it takes 4 pixels to make a color dot, 1 white dot in 2 million still isn't too bad.

I have a 5mp Sony with at least 1 white spot.  I know where it is and fix it before going on.  One isn't much of a problem, but I would think it woildn't take too many more to be a real hassle.

[Howard Smith]

I have seen that the estimate death rate for hospital surgeries is 1 in 100,000 to 300,000.  Considering the cost and consequences, a dead pixal in your new $2000 8mp camera isn't too bad compared to other generally accepted risks.

[Howard Smith]

Stefan, I am sorry you are so offended.  The point was only to put risks into perspective.  Most people don't worry about what they should be concerned about, and take some very risky things totally as givens.  I any only guessing, but I would think it is more likely the camera will not work at all than every pixel is perfect.

I can die from having a wisdom tooth or tonsils removed, but I go ahead.  Then I fret about one dead pixel in 8 million.  I need to keep things in perspective.  I knew a woman who was afraid to fly.  So she drove her car from LA to NY and back.  Not too smart from a risk (expected result of a safe round trip) perspective.

[Robert Roaldi]

dpw wrote

I spoke to Canon UK tech support today to ask what they thought. They informed me that on a new camera, all CCD pixels should work. On LCD screens they have a tolerance of 0.01% total pixel number. On CCD, they expect 100%

Thanks for the follow-up. I am kind of glad to hear that.


Howard, I don't think it's a matter of fretting about the one pixel in 8 million. If the camera was 7 years old and I had bought it for $200 second hand, I could live with having to "fill-in" the pixel in post-process. Or at least it's a cost/benefit trade-off decision I can make for myself. But I really think it's not acceptable in a new camera that's under warranty. It is a defect.

[Howard Smith]

I agree.  It is a defect.  Under warranty, it should (and apparently was) replaced.  The replacement had the same defect.  The cost of Canon finding each defective pixel in each production camera would likely be extremely high compared to setting up a manufacturing program that has a very low actual failure rate and then let the consumer find the last defect(s).

Look at MTF curves.  The tangential and saggital curves should meet at the center of the lens.  They frequently don't.  This difference is usually due to a manufacturing defect, misaligned lens elements.  I suspect that if you had your new Canon lens tested and it showed this defect, Canon would happily take it back and give you another (untested) lens.  The cost would be substantial, so you don't do that.  Canon doesn't either.

I bought a Texas Instruments calculator years ago.  The "8" key didn't work.  I took it back.  They tried the "8" key and it didn't work.  The technician tossed it in the trash can and gave me a new calculator.  He said it is way too expensive to fix it, so just trashed it.  He didn't even take the battery out.

The bottom line is manufactures sell and consumers buy defective merchandise all the time and the vast majority of defects go unnoticed or are tolerated.  It simply isn't cost effective for manufactures to make a 100% defective free product.  It would mean completely testing each production unit.  And guess who pays for that?  Much cheaper for everyone to let the consumer do the QA.

[Howard Smith]

It is starting to sound like that even if Canon "expects" all the pixels to work on a new camera, it is acceptable to them to sell a camera with a dead pixel or two.  I would like to know what happened to the returned cameras.  Where they thrown away, refurbed, or just resold?

[dpw]

I did ask the sales assistant what would happen to the thrid camera as all the accessories were still boxed, and it could still be sold as new. After some hesertation, he said that it would also be sent back to Canon.

Robert - the dead pixels don't show on the LCD screen or EVF as they both have a resolution of 235,000 (I think). During my last visit, I took some pictutes in the shop and loaded them into Adobe Elements using one of their machines.

I'm not quite sure what i'm going to do for a digital camera now. I may tend towards the D10, however I didn't want anything that big.

[Robert Roaldi]

The description above about mapping out bad pixels is reminiscent of mapping out bad blocks when formatting hard drives. Except that bad blocks are then never used by the drive and never affect data quality. Mapped out pixels can affect picture quality, to the extent that more than the normal interpolation is being performed to fill in those pixels.

As others have stated above there are work-arounds for living with a bad pixel or two, which are more or less easy to implement depending on what posr-processing software one uses. But I would still resent having to do so with a new camera. Actually, I would resent having to do it at all but that's just me. If a buyer was told about this up front and it was an accepted industry practice, that would be another matter. I don't know if the marketplace is generally aware of this issue, however.

It brings me back to one of my original questions about buying second hand equipment. When I will be shopping for a 2nd hand digital camera 4-5 years from now, how can I determine how many pixels are mapped out, if any? If there are one or two and the price is right, well, that might be ok, at least it's my choice to make. But if there are 100 or 1000 mapped out, I'd want to know and it's not something I might be able to notice by taking a picture or two in the store, unlike dead or stuck pixels which I might detect more easily. I am not obsessing about this but it strikes me as another thing to think about and plan for since I tend to only buy 2nd hand.