In the past year or so we started to noticed that noise reduction algorithms camera makers were using are starting to evolve. Around the time the Nikon D200 was released to the market, everyone in the japanese camera industry were coming up with something called chroma noise reduction. Prior the Nikon D200, camera makers have done some amount of chroma noise reduction, but the Nikon D200 was the first DSLR to actually use huge filters with very aggressive strength on chroma data. Canon’s DIGIC II is using what we call, the old age noise reduction algorithm, what looks like limited sized filters on chroma and luma data. This age is now over, with the DIGIC III having the “New age” or “New generation” system that can filter chroma data very aggressively, Canon is now catching up to the Nikon, Fuji and Panasonic.

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Evaluating algorithms

Evaluating Canon’s new noise reduction algorithms is easy if you have access to the engine that runs them (DIGIC III), which we don’t. Our job won’t be so easy, and we’ll have to be a little bit more creative. First we have to find the perfect candidate to compare Canon’s new noise reduction algorithms. This candidate can only be the Nikon D200, which uses the same type of new age noise reduction algorithms.

Same signal

Signal level and sensitivity of the sensor are in fact what the noise reduction algorithms receive as their input data. In order to even things out between the two sensors (Mark III and the D200), we had to find an ISO level which will produce the same noise level in both cameras. The input level needs to be as similar as possible. We also wanted to ensure the image will have sufficient noise levels in order to make things tough for the noise reduction algorithms – a high ISO level was needed. The first thing we did was to photograph our test scene with both cameras, using all ISO settings in 1/3EV steps. We then striped all RAW files from their headers and processed all files with a very basic demosaicing algorithm, white balance and basic Gamma. The result is a set of images that have no noise reduction applied. Because the EOS Mark III RAW files have not been applied with any black-level and their white point is not the same as the Nikon D200 – finding the same signal level wasn’t easy. We had finally come to the conclusion that we should use the Nikon D200 at 1600ISO and the Canon EOS Mark III at 3200ISO to match the input signal levels.

Edge enhancement (Sharpening)

Edge enhancement, or sharpening, influences edge noise and edge look quite a bit. Both Nikon and Canon do their edge enhancement differently, but we have to make sure the levels of the edge enhancement are close. After testing different levels of in-camera sharpening, it was clear that the Canon EOS Mark III is to be set to sharpening 2 and the Nikon D200 will be set to Normal sharpening. At 1600 ISO, Medium High on the Nikon D200 was too high, compared to the EOS 1D Mark III. Note that you may see more white hallows on Canon’s side, but this is just their way of sharpening.

Our scene and 200% view

This is our scene which we are going to use for this article. It is not an easy scene, as it was specially designed to fail noise reduction algorithms. The crops taken from this scene are 200% view. Although you may call us Pixel Peepers, but we believe 200% is the minimum view needed in order to analyze algorithms. If you find this bothering, you might find low quality noise reduction algorithms good enough for you.

The scene was shot with both cameras at the same time. Due to crop factor differences, we moved the EOS 1D Mark III forwards to match the size of the objects in the scene. This results from the EOS 1D MKIII are having a small advantage in distance. Also note, we set contrast of the EOS 1D Mark III to -2 to match the contrast of the Nikon D200, as the Nikon D200 High contrast setting is too high.

Here is the full settings we used:
Canon EOS 1D Mark III: 1/400, 50mm(EF 2.5)@f8, JPEG L, 3200ISO, picture style – standard, contrast -2, sharpening 2, sRGB.

Nikon D200: 1/200, 50(f1.4)@F8, JPEG Fine, 1600ISO, Tone – Normal, Sharpening – normal, sRGB (Mode I).

We’ll also be showing you crops with no noise reduction. Those crops were acheived by using DNG demosaicing and some matlab for WB and Gamma functions. We used the SAME gamma the manufacture used to produce the image, as gamma has huge impact on noise. Please note that there is no easy way to reproduce Canon’s colors (which also affects noise), so those crops will have a different color.

The Results

Before examining the results, we need to clarify the difference between the two types of noise recudsion the EOS 1D Mark III uses. C. Fn II-2 allows you to set the noise reduction ON or OFF, but rest assured that noise reduction is never really turned OFF. What it does mean is that the camera will do a simpler noise reduction, much similar to what DIGIC II was capable of. Switching C. Fn II-2 to ON means the camera will apply the new, more agressive noise reduction, which is way more modern. The down side is mostly speed, as it turns out two DIGIC III chips can not process RAW images fast enough to clear the buffer. The buffer depth reduces from 99 images to just 14. Much to our disappointment, Canon had to set C. Fn II-2 to OFF by default, and produce relatively low image quality.

• RGB View
• Luma View
• Chroma View

EOS 1D Mark III NR OFF	EOS 1D Mark III NR ON	EOS 1D Mark III RAW (No NR)

EOS 1D Mark III NR OFF	EOS 1D Mark III NR ON	EOS 1D Mark III RAW (No NR)

EOS 1D Mark III NR OFF	EOS 1D Mark III NR ON	EOS 1D Mark III RAW (No NR)

As you can see from the results, when the C. FnII-2 is set to OFF there is quite a bit of Chroma noise. This type of noise reduction also reduces a little bit of details compared to the RAW image with no noise reduction applied. From the large color spots in the NR OFF image you can see that the filter applied on the data is is not large, meaning the filter is not averaging strongly on large regions. However, we are really impressed by the very good edge detection and preservation.

Turing C. FnII-2 ON really upgrades the image quality. This type of noise reduction splits the data into luma (brightenss) and chroma (color) images. Canon then filters Chroma data with very large (huge, probably) filters, averaging very strongly while preserving edges. Luma data also gets the same treatment but with a very fine and gentle filtering. Once Chroma noise is out of the way all that is left is strong monochromatic grain and some demosaicing noise (patterns that are a result of demosaicing). Luma noise is then filtered gently to produce fine looking grain. This is the part where the camera maker needs to find the balance between details and grain (luma noise).

With high ISO images, small and fine details are embedded into noise, so over filtering will lose more of those details but will also produce a flatter, grain-less images. Filter too little, and you end up with a lot more luminance noise, alongside preserving those details. A good balance is needed to achieve the best possible result.

There is one more variable in the equation, and that is edge detection. The trick of noise reduction in to filter evenly on flat areas but filter along the edge when an edge is detected. The better the camera maker could do this, the more details will be preserved while treating flat areas with stronger filtering.

From the results above you can see that this time, lunch is indeed (almost) free. For little less fine details you can get an image free of color noise. When C. FnII-2 is set to ON you indeed get a modern, top notch, excellent noise reduction. Too bad Canon hasn’t made their best effort to make DIGIC III fast enough for 10MP with 10 frames per second (although this is actually a buffer size issue. the actual processing time is probably less even with C. FnII-2 set to OFF).

Canon vs. Nikon, here we go

Nikon had their bets on new generation noise reduction for some time now. As you may know, Nikon had a few problems with their own sensors. With pixel sizes getting smaller and smaller every year as camera resolution increases, the best way to deal with image noise is to have less noise to begin with. But since that is out of their reach, now generation chroma noise reduction is the way to go.

The Nikon D200 was the first DSLR with new generation noise reduction and this was over a year before Canon’s DIGIC III. So Nikon is probably going to improve their algorithms in the next pro DSLR camera. Note that the Nikon D80 and Nikon D40x don’t seem to use an improved algorithm, but only seem to use different configurations for the same algorithm.

Chroma filtering strength

IIt’s not easy to filter an image fast and effectively, a camera maker may not be able to filter the data to a completely flat result (even though this is not always necessary). So first we’ll look at the strength of the chroma and luma filtering. Please note that we have this detailed data on chart which you can view here.

• RGB View
• Luma Viev
• Chroma view

EOS 1D Mark III NR ON	EOS 1D Mark III NR OFF	EOS 1D Mark III RAW (No NR)
Nikon D200 NR Normal	Nikon D200 NR OFF	Nikon D200 RAW (No NR)
Black	Gray	White

EOS 1D Mark III NR ON	EOS 1D Mark III NR OFF	EOS 1D Mark III RAW (No NR)
Nikon D200 NR Normal	Nikon D200 NR OFF	Nikon D200 RAW (No NR)
Black	Gray	White

EOS 1D Mark III NR ON	EOS 1D Mark III NR OFF	EOS 1D Mark III RAW (No NR)
Nikon D200 NR Normal	Nikon D200 NR OFF	Nikon D200 RAW (No NR)
Black	Gray	White

The crops above are taken from the Colorchecker 24 chart that is on the scene. It is clearly visible just how good the chroma noise reduction in flattening chroma data. Take a look at the NR OFF setting of the EOS 1D Mark III and you’ll see why images taken with this setting have much more color noise. It looks like Nikon has reduced chroma noise, or flattened chroma noise a bit better than the EOS 1D Mark III. You can hardly see the difference in this type of image view but it’s there. Of course, NR OFF setting of the Nikon D200 isn’t really OFF. It’s quite the same with smaller amount of filtering. Below is anther crop from our scene that better illustrates that the EOS 1D Mark III leaves a bit of color stains behind. Color stains are very bad, because they can really disturb the viewer.

Canon EOS 1D Mark III NR ON	Nikon D200 Normal

Color glow at edges

One of the biggest problems the chroma noise reduction has to deal with is false colors at edges. Because of the large and aggressive filtering on the chroma data, edges are bound to leak from their original position, creating color glow around the edge.

• RGB View
• Luma View
• Chroma View

EOS 1D Mark III NR ON	EOS 1D Mark III NR OFF	EOS 1D Mark III RAW (No NR)
Nikon D200 NR Normal	Nikon D200 NR OFF	Nikon D200 RAW (No NR)

EOS 1D Mark III NR ON	EOS 1D Mark III NR OFF	EOS 1D Mark III RAW (No NR)
Nikon D200 NR Normal	Nikon D200 NR OFF	Nikon D200 RAW (No NR)

EOS 1D Mark III NR ON	EOS 1D Mark III NR OFF	EOS 1D Mark III RAW (No NR)
Nikon D200 NR Normal	Nikon D200 NR OFF	Nikon D200 RAW (No NR)

If you’ll toggle between the EOS 1D Mark III and the Nikon D200 at Chroma view, you’ll see that the EOS 1D Mark III does show more glow than the Nikon D200. The edges on the Nikon D200 are somewhat sharper. However, if you take a closer look, you’ll see that the Nikon D200 also shows some artifacts along the edges where the EOS 1D Mark III does not. Also, on the right bottom patch at the upper edge you can see a strong orange line along the edge. This line, along with those small artifacts, is going to show up at RGB view (the final image) as color artifacts. That line will show as stronger orange-yellow line on the Nikon D200. Although Canon is showing a bit more glow here, I am quite impressed by Canon’s artifact free edges. Nikon could probably achieve the same affect by blurring the Chroma data a tiny bit.

False colors at edges

Edge detection yields yet another problem. If an edge was not properly detected while chroma filtering, the filter will not average that undetected part of the edge. The result is small color stains and edges that are filled with color noise.

• RGB View
• Luma View
• Chroma View

EOS 1D Mark III NR ON	EOS 1D Mark III NR OFF	EOS 1D Mark III RAW (No NR)
Nikon D200 NR Normal	Nikon D200 NR OFF	Nikon D200 RAW (No NR)

EOS 1D Mark III NR ON	EOS 1D Mark III NR OFF	EOS 1D Mark III RAW (No NR)
Nikon D200 NR Normal	Nikon D200 NR OFF	Nikon D200 RAW (No NR)

EOS 1D Mark III NR ON	EOS 1D Mark III NR OFF	EOS 1D Mark III RAW (No NR)
Nikon D200 NR Normal	Nikon D200 NR OFF	Nikon D200 RAW (No NR)

By toggling between the EOS 1D Mark III and the Nikon D200, you can see that the EOS 1D Mark III results look better. In both sides of the face, inside the left eye and left eyebrow of the Nikon D200 image you can see color noise leftovers, right on the edge of the details. The EOS 1D Mark III result simply don’t show those false colors. By switching to Chroma view you can clearly see the problem, most of the strong edges of the Nikon D200 contains artifacts, along the edges (inside the eyes, in both sides of the face, etc). Those artifacts will look as color on the RGB view of the image, the EOS 1D Mark III does a better job here.

However, on the right side of the right eye the EOS 1D Mark III result does look odd in RGB view. There is some color noise and some chroma loss (skin tone color loss). switching to Chroma view, you’ll notice some holes in the data, clearly something confused the EOS 1D Mark III algorithm. This does not happen with the Nikon D200.

One last interesting note, the EOS 1D Mark III seem to filter luma data better, switch to Luma view, you’ll see that the image looks clearer. The edges seem to be better preserved, which helps the image look less water colored, as some noise reduction algorithms do.

• RGB View
• Luma View
• Chroma View

EOS 1D Mark III NR ON	EOS 1D Mark III NR OFF	EOS 1D Mark III RAW (No NR)
Nikon D200 NR Normal	Nikon D200 NR OFF	Nikon D200 RAW (No NR)

EOS 1D Mark III NR ON	EOS 1D Mark III NR OFF	EOS 1D Mark III RAW (No NR)
Nikon D200 NR Normal	Nikon D200 NR OFF	Nikon D200 RAW (No NR)

EOS 1D Mark III NR ON	EOS 1D Mark III NR OFF	EOS 1D Mark III RAW (No NR)
Nikon D200 NR Normal	Nikon D200 NR OFF	Nikon D200 RAW (No NR)

Here is anther example where, by toggling between EOS 1D Mark III NR ON and Nikon D200 Normal, you can see the Canon can preserve color edges better. The Nikon D200 result has quite a lot of false colors artifacts – around the yellow ball of string, near the shadows and at the left end of the battle label. Looking at Chroma view, you can see that the Nikon D200 chroma edges are sharper with more artifacts. Once again, those artifacts are showing up as color noise leftovers at RGB view.

Chroma reduction

A little trick to further reduce color noise is to suppress chroma (color) as a function of luminance. This means that from a certain low levels of luminance, the algorithm will deliberately lower the chrominance of the area to suppress color noise. Although quite smart, we don’t like this so much, as sometimes there are color less “holes” in the image.

• RGB View
• Luma View
• Chroma View

Canon EOS 1D Mark III NR ON	Nikon D200 NR Normal

Canon EOS 1D Mark III NR ON	Nikon D200 NR Normal

Canon EOS 1D Mark III NR ON	Nikon D200 NR Normal

It seems that both Nikon and Canon are using this type of method to reduce color noise at the dark parts of the image. However, Canon seem to do this less and better than Nikon. We are quite pleased to see that, as Nikon’s approach was far too aggressive to our taste.

Edges and details

The first thing photographers think about when they hear “Noise Reduction” is “loss of details”. We tend not to get scared from losing detail, mostly because we know the strong hard edges will be preserved by advanced noise reduction algorithms. Below you can see an example of that, those lines are 2-3 pixel wide. Move you mouse over the images to toggle between the original JPEG image and the RAW image we processed without any Noise Reduction.

Canon EOS 1D Mark III NR ON	Nikon D200 NR Normal

The differences in contrast you can see is due to edge enhancement applied on the JPEG images. The noise reduction algorithm is smoothing the signal along the edge, resulting in a smoother image. This example shows you that noise reduction algorithms can easy preserve hard edges. So if you shoot 1600ISO or 3200ISO, those hard edges will most probably be preserved, enabling you to print good quality image out of both cameras.

However, saving as much fine details as possible will result in an overall better image. This is not very easy when those fine details (the signal) are very close to the variation of noise (noise signal). Then, you need some really good engineering to save those signals from being destroyed.

Canon EOS 1D Mark III NR ON	Nikon D200 NR Normal

The example above shows that it is very hard to preserve fine edges. By moving your mouse on the images (Luma only) you can see that Canon was able to preserve signals extremely well, as opposed to the Nikon D200, which has killed any details that were present in the RAW data. This is very impressive indeed.

Canon EOS 1D Mark III NR ON	Nikon D200 NR Normal

Here is another example of the exact same thing (Luma only). Canon was able to preserve fine edges very well while Nikon averaged out those details that where quite strong in the RAW data. If we would need to guess, we would say Nikon performs their noise reduction AFTER gamma, which means they do in on 8 bit data. Gamma really messes around with single to noise ratio so this would probably be the reason Nikon was unable to preserve those fine edges.

There is one more aspect to be adressed, and that is how both the Nikon and the Canon are preserving edges in the shadows. It is relatively easy to preserve fine edges in the highlights because the signal to noise ratio there is much better. In the shadows it is a whole different ball game.

Canon EOS 1D Mark III NR ON	Nikon D200 NR Normal

It is interesting to see that the RAW data from the EOS 1D Mark III has a better signal at the shadows, so it is hard to call out a winner here. Both cameras have lost some details, with the Canon seeming to find those strong edges and filter them correctly, while the Nikon’s signal seem to be too disrupted. This is also true elsewhere around the image, we were unable to find a good example because Canon always seemed to have a better signal at midtones and shadows already on the RAW data. So we have to say Canon’s CMOS sensor (and size) has the upper hand here by providing a better signal.

Grain

When chroma noise is reduced almost completely what is left is luma noise (monochromatic noise). This luma noise has to be filtered gently in order to have a pleasant looking result. If filtered too hard, the whole image will look too flat and will have the famous “water color affect”. If filtered too weakly, the image will look too grainy. So a precise amount of filtering is required to produce a pleasant grain result.

EOS 1D Mark III NR ON	EOS 1D Mark III NR OFF	EOS 1D Mark III RAW (No NR)
Nikon D200 NR Normal	Nikon D200 NR OFF	Nikon D200 RAW (No NR)
Black	Gray	White

By toggling between EOS 1D Mark III NR ON and Nikon D200 NR Normal, it is clear that Canon is leaving a bit more sharper grain in the mindtones. However, the Nikon seems to leave more grain in the shadows, where the Canon leaves a more smooth result. We think Canon has the Grain a bit more balanced than Nikon. We never liked the fact that the Nikon D200 has so much Grain in the shadows. These observations reflect in the results we have on our noise analysis database.

Final words

Canon has really done it this time. The new noise reduction algorithm is working really well. Of course, both Canon and Nikon have their issues that which need to work on. We are not very happy with the vague but large color stains the Canon is leaving behind. Nikon seems to filter chroma more aggressively. Nevertheless, the Canon’s ability to filter chroma edges really well and to filter weak details signals correctly is very very impressing. We think Canon has also done a better job tuning those algorithms to produce a more pleasing result.

Nikon really has a lot of work ahead. The two issues that are bothering us the most are the false colors at the edges and the fact that there is just too much grain at the shadows. As we said before, small details are not as important in high ISO image as the pleasing look of the image.

Algorithms aside, it is really amazing to see how good the EOS 1D Mark III CMOS sensor is. The signal levels are way better than everything we have seen in the past. Canon’s ability to produce those good SNR levels from a CMOS sensor has come a very long way, and it is now way above the competition.

Hopefully you are now able to better understand how complex noise reduction is and how really well it could work if properly engineered. You can only take advantage of those well engineered algorithms if you use the camera’s jpeg processed file. Naturally, shooting RAW and processing the image with RAW software, such as Adobe Camera Raw and Aperture, will not produce these results. You may use the manufacture’s RAW software which is Canon Digital Photo Professional for Canon and Nikon Capture NX for Nikon. Those RAW softwares are producing very good results, although they are tuned somewhat different than the cameras. We will write about this sometime in the future.

I’ve read a lot of articles about image sensors over time. Many of them were talking about something called “dark current noise”. dark current is electrons that are captured by the sensor but not as a reaction to light. This is actually unwanted signal the sensor has picked up. This unwanted signal has a fluctuation, which means this signal is creating noise when looking at more then one pixel. Because this signal is very weak, noise signal is only building up to a noticeable level when the exposure time is very long. Further more, dark current level is said to be reduced substantially if the sensor is cooled down.
We are only interested with what happens when we take noise measurement in our labs for our noise analysis database. The temperature in our labs is monitored and kept at a certain level. We have an air condition and a thermometer, so we are pretty much covered, and we always try to bring room temperature to about 68 °F (20 °C) when we do noise measurements. The question is, how strictly do we need to follow the 68 °F rule? Does temperature in an exposure time of 1/30 makes any difference? Does dark current noise effect our noise readings?

In order to test this, we made a simple test. We took two noise measurements, one when the room temperature was 66.2 °F (19 °C) and a second test when heating the room temperature to 84.2 °F (29 °C).
For this task we used the Olympus E-330 DSLR, set to 1600 ISO with Noise reduction set to OFF. The E-330 is using a CMOS sensor, and a quite noisy one, if I may add.

The full procedure of the test is as followed:

1. Set the room temperature to 66.2 °F (19 °C)
2. Take 3 JPEG shoots of the GretagMacBeth ColorChecker 24 test chart, exposure time is set to 1/30 and the camera is set to 1600 ISO NR OFF
3. Set the room temperature to 84.2 °F (29 °C) and let the camera warm up for about 45 minutes.
4. Take the same 3 image as paragraph 2, same exposure time.
5. For each temperature, read std. from the 6 monochromatic zones of the ColorChecker chart and average every set of 3 shots out.
7. Plot the Luma values to a graph (shown below).

The table below shows the full noise readings, as you can see there the std value is slightly lower in about every zone of the chart. So the theory above could be just true. In any way, we have determined that room temperature is not critical when measuring noise, and that dark current is nothing to worry about at an exposure time of 1/30.

The pixel size of the Canon EOS 400D is 5.7µm, small as all other 10 MP DSLRs. The Canon EOS 30D has a 8MP sensor so its pixel size is bigger, 6.4µm. Keeping in mind those two cameras are using the same DIGIC II image pipeline, an high ISO scene should be really interesting. Can the old DIGIC II cope with the extra pixel-size weight?

Canon EOS 400D: Jpeg Fine, PS: Standard, AutoWB, ISO1600, 1/100,
Canon 50mm@f9
Canon EOS 30D: Jpeg Fine, PS: Standard, AutoWB, ISO1600, 1/125,
Canon 50mm@f9

Canon EOS 400D	Canon EOS 30D

Sharpening

Due to the picture style system, the sharpening levels are equal in both cameras. If we compare it to 100 ISO, that sharpening levels were somewhat lowered.

Details

The 10MP sensor of the Canon EOS 400D has a small advantage. If we watch carefully we can find a few details that are softer in the Canon EOS 30D.

demosaicing, false colors

These symptoms are reduced when shooting in high ISO. Although the Canon EOS 30D has a little bit more problems at cut 13.

Contrast and color

Again, due to the picture style system the shadows and contrast are pretty similar.

Noise reduction

We didn’t expect to see much difference in the noise reduction area considering that these are the same algorithms of the DIGIC II that are doing the job. There is little differences in the dark areas of the image, where signal to noise ratio is low. In these areas we can see a tiny bit of an advantage to the EOS 30D due to it’s lower MP, having lower pixel density. As all Canon cameras based on the DIGIC II there is a small amount of chroma noise.

Notes

It seems that Canon has stretched the limits of the DIGIC II with the EOS 400D. We would say that 8MP is the acceptable limit of the DIGIC II. The EOS 30D has less noise and an almost similar amount of detail. It’s hard to say if the price of some noise is worth the addition of some detail.

Lab Plot