Tuesday, 18 March 2008

Canon 5D and 'Hot' Pixels

So I've just got this brand-spanking new 5D, right. And I've taken it out on its first landscape shoot to a favourite spot of mine where I 'test' a lot of my gear and put it through its paces.

I'd heard, and read, a lot about the 5D's low noise - especially with long exposures, so I was very keen to experience this for myself. I enabled the custom function that extends the camera's ISO capabilities, and set the camera to 50. I also put long exposure noise reduction to 'on', and set my tripod up for some long exposures.

The previous night I had been reading a few commentaries on the internet - in particularly one from Ken Rockwell - that claimed there is little to no benefit in shooting RAW. I had been surfing on this topic because, to my horror, I discovered that shooting RAW with the 5D only gives me about 220 images on a 4 Gig card! Whereas turned to high quality jpeg nets upwards of 1000 images. That's more like it, I thought.

So anyway, the high quality jpegs were in the bag (so the speak), and I headed home to marvel at them in Lightroom. And marvel at them I did. Wow, the sensor on the 5D is incredibly noiseless at ISO 50 - even with 30 second exposures. I was impressed.

But hang on a minute. What are those little spots through the images? They seem to be in exactly the same place all the time. Don't tell me I've got dust on the sensor already? I haven't even changed the lens on it - ever. A closer look was called for.


A 'Hot' pixel from the 5D - at 300% enlargement, from a 15 second exposure.

On closer inspection it turned out that dust wasn't the problem at all. My brand spanking 5D has 'hot pixels' - about 6 of them, that show themselves during long exposures (of about 2 seconds or more).

I was gutted, crushed, inconsolable. How could this be? I'd never had this happen on any of the dozen or so camera bodies that I've used or tested over the years. Yet here it was, on the supposed 'King" of them all, the 'noiseless' 5D. My initial thought was to send the camera straight back to Canon and complain bitterly. Luckily, I slept on it over night and decided to do a little more investigating.

Internet discussion on similar problems with the 5D (and other cameras) shows mixed views. About half who responded to another disgruntled 5D owner with hot pixels said 'send it back and complain bitterly'. My thoughts exactly.

But there were others who claimed that hot pixels were to be expected from all camera sensors, and a 'few' hot pixels out of 12.8 million isn't too bad. And anyway, they said, there is a difference between 'stuck', 'dead' and 'hot' pixels. Dead pixels are just that - dead, and won't show any information no matter what settings the camera is on. They always appear as black spots, beause no information is reaching them at all. Stuck pixels are the opposite - the always appear as bright white, because the are 'stuck' and blow out the information they receive. Whereas hot pixels only show up when the exposures are longer (typically over 1 second) and function perfectly normally on speeds below this.

Further testing with my 5D showed that the sensor was indeed fine under 'normal' shooting conditions. No bright or 'stuck' pixels at all. It was something of a relief. But I still wasn't happy.

Then I hit upon a site that claimed cameras could be 'cured' of hot pixels. Apparently all sensors do indeed have them, but they are 'mapped out' before leaving the factory. By activating 'sensor cleaning' from the menu with the lens still on, the camera 're-maps' those pixels, and viola - no more hot pixels. Trouble is, it didn't work.

Lots of people claim it does fix hot pixels, (or maybe it fixes 'stuck' pixels) and I have no cause to doubt them. Maybe I did something wrong? But whatever the case, it didn't fix my hot pixel problem. So I'm sending my 5D back - right?

Well no, actually, because I followed the final solution to the whole 'hot' pixel problem and it worked a treat. Shoot RAW. That's it. Just shoot RAW. That was my problem all along (thanks for nothing Rockwell). I ALWAYS shoot RAW, that's why I've never come across this problem before. I can practically guarantee my other cameras have also had a few hot pixels, but the RAW processing 'maps' these out so they don't appear in the final image. Works great.

So now I have a perfectly functioning 5D, and yet another reason to shoot in RAW. And the solution to the 200 odd images I can store on a 4 Gig card? That one's easy. I've just purchased an 8 Gig card as well.

7 comments:

  1. Wayne. Thanks for this blog post. Somehow my google search brought you up first. I have a 5d M1, brand new with one hot (red) pixel at normal exposures, and many more (about 10) at longer exposures. I am shooting RAW only. The first time I tried the sensor cleaning method it didn't work, but then I tried it again and left it on longer (about 45 seconds), and it worked! Now I just have to go edit that one hot pixel in the 500 photos I just shot :(

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  2. Hi Stephen

    Glad you got something out of the post. I write these never expecting (maybe hoping) that anyone will read them, so it's always nice when I get a comment back that proves at least one other person in the world has seen my blog :-)

    Good luck with the 500 other images.

    Wayne

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  3. I was camping last friday and did tons of dark / night shots. In the jpgs I surely do see TONS of these hot pixels, some of them shades of magenta, some whitish. Anyway after reading your post, it makes me want to go back and check out the RAW versions (I've been previewing jpg thus far) -- thanks for the tip

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  4. Wayne, I have hot pixels on my 30D that show up in long exposures and I ALWAYS shoot RAW. I suspect that your hot pixels are actually being "processed out" by your RAW processing software. I know that Adobe Camera Raw eliminates most of my hot pixels when I open a file but Canon's Digital Photo Professional does not. I've read various opinions about why/how ACR "fixes" these hot pixels, but I think the most logical is that the "fix" is just a side effect of noise reduction that ACR perform's by default on RAW files. My hunch is that you do not use Canon's software and that if you were to use Canon's software to process your RAW files your hot pixels would "come back".

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  5. Oh, forgot to mention that my 30D (and I'm guessing your 5D as well) has a custom function that is used to eliminate noise (and hot pixels) automatically in camera. When the function is turned on, long exposure shots are immediately followed by an equal "shutter speed" shot with the shutter closed. The camera uses the closed shutter shot to eliminate noise from the real shot. The obvious disadvantage is that long exposures take twice as long.

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  6. If shooting in raw, load a raw file into adobe camera raw, and ACR will automatically remove any hot pixels on the fly for you almost instantly. This is a good benefit since there is no other softening or noise reduction performed.

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  7. Thanks for review, it was excellent and very informative.
    thank you :)

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Thanks for your reply. I really appreciate you taking the time to comment on this post. I will get back to you as soon as I can.
Thanks again
Wayne