As I was hoping, several people chimed in to share their knowledge in response to my 5D2 noise test article as well as to provide links to additional resources and discussion on the web. Thanks for that! Based on the additional information I have revised my original article with the following addendum. (If interested you can read the entire article at PhotoCascadia.com)
It turns out there isn’t any voodoo ISO magic happening at multiples of ISO 160 in Canon cameras. The most important factor in low noise images is still capturing the most photons of light. This is achieved by exposing the sensor to light for the longest time possible without overexposing highlights (exposing to the right). Lower ISOs and exposing toward the right on the histogram enable capturing the most photons (signal) with the least noise. The higher the signal to noise ratio (S/N) the better.
The noise seen in the test images in my article(and in all the other similar tests I have seen on the web) is what is called pattern or read noise. Pattern noise is the noise that occurs during the creation and processing of the RAW file and is independent of the incoming signal (photons). Taking a photo with the lens cap on captures zero signal (photons) so all we see is the pattern noise. Without looking at how signal and noise measure up to each other we don’t have a reference for final image quality. We want low pattern noise, but not at the expense of less signal (fewer photons).
After digging a little deeper it seems that most agree that native ISO on Canon cameras is ISO 100 and not ISO 160 as some have claimed. All ISO settings other than 100, 200, 400, etc. are derived from these analogue ones by digital manipulation. This information corresponds with scenario #2 I outlined in my article. According to ejmartin on the Luminous Landscape Forum, “the 5D Mark II obtains ISO 160 by taking an image at ISO 200 and multiplying all the digitized values by 0.8. You could do the same by exposing ISO 200 to the right and dialing in -1/3 stop of exposure compensation in the raw converter.” It follows then that the best signal to noise ratio you can get comes from exposing to the right at ISO 100.
In a separate thread on the Luminous Landscape forum ejmartin makes a clear cost/benefit analysis of higher ISO settings. He says, “There is less (pattern) noise at 160 than there is at 100 for the 5D2. This is because the amplifier/ADC noise is about the same at ISO 200 as it is at ISO 100, and ISO 160 is obtained from ISO 200 by multiplying all the output values by 0.8 so the (pattern) noise in raw levels will be about 20% less at 160 relative to 100. However, the photon count that saturates the raw data is 60% less at 160 than at 100. So, 20% less (pattern) noise at the cost of 60% less photon capacity. If you have 60% less photons [due to lower light], then it makes sense to use 160 instead of 100. If your shooting conditions allow the (longer) exposure, better to use 100 — the benefit of more photons outweighs the disadvantage of higher (pattern) noise. Again, the goal is the highest S/N ratio in actual photographs, not the lowest noise with no signal (unless your interest is photographing the inside of your lens cap as an end in itself).”
And what about loss of dynamic range at higher ISO settings? It seems this can be an issue, but is different from camera to camera. According to DxO Labs data the 5D Mark II doesn’t experience a significant loss of dynamic range until beyond ISO 800. Other cameras may experience a significant drop in DR performance sooner so it would be worth checking your camera’s stats on the DxO Labs site.
So, here’s what I take away from all this:
* More photons trumps less pattern noise, so use lower ISOs when possible and expose to the right to get longer exposure times and capture more photons (signal). If you are exposing to the right (without clipping highlights) then 100, 200, 400, 800 are your best bet. Shooting ISO 160 just means that the camera is shooting automatically exposing ISO 200 to the right and dialing back the exposure 20% in the RAW file.
* For those of us who have been conditioned to shoot ISO 100 at all costs, you can shoot at ISO 160, 200, 320, 400, and 640 when you need the extra shutter speed and still maintain a good signal to noise ratio, at least with the 5D Mark II. Increased pattern noise at 125, 250 and 500 caused by manipulation of the RAW data is problematic because it lowers the S/N ratio.
* There is some loss of dynamic range at higher ISOs but on the 5D Mark II it is minimal until you go higher than ISO 800. Still, ISO 100 will give you the most dynamic range.
NPN member Luis Argerich offered a very helpful ISO acronym: If you want minimal noise the recipe is simple: ETTR & ITTR . First ETTR (expose to the right). Go for as long an exposure at the lowest ISO you can without clipping highlights. Collecting more photons defeats noise. If the shot requires a faster shutter speed then move the ISO to the right (ITTR) keeping your histogram values as far right as possible.
Wow, fantastic assessment Sean, thanks for putting all the research time into this, many will benefit. I think I'll break it down in a simple way for me to remember: if I need a tripod, ISO 100, because I'm probably at f/14 and 20 seconds, etc. If I'm shooting off a tripod in fairly bright light, ISO 160, and then multiples up as light dims. Same for video.
Hey Sean, I just came across this new article in the June Pop Photo webpage, and it has images of the noise at each ISO from a VIDEO standpoint. I was surprised to see ISO 1250 cleaner than 125! I recently shot some video at 1600 and it looks horrid, just like the article sample. But still shots at 1600 with a touch of the new noise reduction in ACR look super.
Discussion
2 repliesIt turns out there isn’t any voodoo ISO magic happening at multiples of ISO 160 in Canon cameras. The most important factor in low noise images is still capturing the most photons of light. This is achieved by exposing the sensor to light for the longest time possible without overexposing highlights (exposing to the right). Lower ISOs and exposing toward the right on the histogram enable capturing the most photons (signal) with the least noise. The higher the signal to noise ratio (S/N) the better.
The noise seen in the test images in my article(and in all the other similar tests I have seen on the web) is what is called pattern or read noise. Pattern noise is the noise that occurs during the creation and processing of the RAW file and is independent of the incoming signal (photons). Taking a photo with the lens cap on captures zero signal (photons) so all we see is the pattern noise. Without looking at how signal and noise measure up to each other we don’t have a reference for final image quality. We want low pattern noise, but not at the expense of less signal (fewer photons).
After digging a little deeper it seems that most agree that native ISO on Canon cameras is ISO 100 and not ISO 160 as some have claimed. All ISO settings other than 100, 200, 400, etc. are derived from these analogue ones by digital manipulation. This information corresponds with scenario #2 I outlined in my article. According to ejmartin on the Luminous Landscape Forum, “the 5D Mark II obtains ISO 160 by taking an image at ISO 200 and multiplying all the digitized values by 0.8. You could do the same by exposing ISO 200 to the right and dialing in -1/3 stop of exposure compensation in the raw converter.” It follows then that the best signal to noise ratio you can get comes from exposing to the right at ISO 100.
In a separate thread on the Luminous Landscape forum ejmartin makes a clear cost/benefit analysis of higher ISO settings. He says, “There is less (pattern) noise at 160 than there is at 100 for the 5D2. This is because the amplifier/ADC noise is about the same at ISO 200 as it is at ISO 100, and ISO 160 is obtained from ISO 200 by multiplying all the output values by 0.8 so the (pattern) noise in raw levels will be about 20% less at 160 relative to 100. However, the photon count that saturates the raw data is 60% less at 160 than at 100. So, 20% less (pattern) noise at the cost of 60% less photon capacity. If you have 60% less photons [due to lower light], then it makes sense to use 160 instead of 100. If your shooting conditions allow the (longer) exposure, better to use 100 — the benefit of more photons outweighs the disadvantage of higher (pattern) noise. Again, the goal is the highest S/N ratio in actual photographs, not the lowest noise with no signal (unless your interest is photographing the inside of your lens cap as an end in itself).”
And what about loss of dynamic range at higher ISO settings? It seems this can be an issue, but is different from camera to camera. According to DxO Labs data the 5D Mark II doesn’t experience a significant loss of dynamic range until beyond ISO 800. Other cameras may experience a significant drop in DR performance sooner so it would be worth checking your camera’s stats on the DxO Labs site.
So, here’s what I take away from all this:
* More photons trumps less pattern noise, so use lower ISOs when possible and expose to the right to get longer exposure times and capture more photons (signal). If you are exposing to the right (without clipping highlights) then 100, 200, 400, 800 are your best bet. Shooting ISO 160 just means that the camera is shooting automatically exposing ISO 200 to the right and dialing back the exposure 20% in the RAW file.
* For those of us who have been conditioned to shoot ISO 100 at all costs, you can shoot at ISO 160, 200, 320, 400, and 640 when you need the extra shutter speed and still maintain a good signal to noise ratio, at least with the 5D Mark II. Increased pattern noise at 125, 250 and 500 caused by manipulation of the RAW data is problematic because it lowers the S/N ratio.
* There is some loss of dynamic range at higher ISOs but on the 5D Mark II it is minimal until you go higher than ISO 800. Still, ISO 100 will give you the most dynamic range.
NPN member Luis Argerich offered a very helpful ISO acronym: If you want minimal noise the recipe is simple: ETTR & ITTR . First ETTR (expose to the right). Go for as long an exposure at the lowest ISO you can without clipping highlights. Collecting more photons defeats noise. If the shot requires a faster shutter speed then move the ISO to the right (ITTR) keeping your histogram values as far right as possible.
Thanks!
Interesing, the physics behind all of this.