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Glen Pitt-Pladdy :: Blog

Canon IXUS 870IS noise tests with CHDK RAW

Those doing serious photography with a dSLR would know all about RAW and it's benefits, but when it comes to Compacts, RAW is almost always absent. It is making a comeback on high-end Compacts, but on older and lower end Canon Compacts it's often possible to add RAW using CHDK.

As an experiment I bought a Canon IXUS 870IS (SD 880IS elsewhere) which apart from being extremely cheap second hand on eBay, has a wide lens - something Compacts generally lack.

The Test

The biggest drawback of a Compact often comes down to some combination of a mediocre lens and a small noisy sensor. The IXUS 870IS boasts ISO1600, so how good is this really? By using the RAW files we can actually see what the sensor is producing and how well the clean-up works.

What I have done is take a subject which has a combination of textures and edges (a brick wall) and process the RAW files for comparison to the JPEG files the camera would normally produce. I have done two versions of the RAW, the first cleaned up with Neatimage before processing and the second untouched.

Compensating for Camera Processing

The camera does a few things which can make testing a bit difficult by applying sharpening, colour adjustments, curve adjustments etc. all by it's self. Some of these (eg. curve adjustments) do seem to cut off the shadows and reduce shadow detail which probably helps hide the sensor noise.

Also, the setup for Neatimage I am using does slightly sharpen the image to help compensate for lost detail from the noise reduction.

To try and level the playing field I have done a few adjustments to the final images:

JPEG
  • Applied white point of 230
RAW via Neatimage
  • Applied black point of 40
  • Unsharp Mask of 0.45 and radius 3
RAW original
  • Applied black point of 40
  • Unsharp Mask of 1.0 and radius 3

The unsharp mask does emphasize the noise at higher ISO with the RAW original, but for comparison, before sharpening the noise level looks similar to one stop lower ISO when sharpened.

The Results

Images in order left to right are:

  • Camera JPEG
  • RAW via Neatimage
  • RAW original

All these are cropped at 1:1 scale.

ISO80

IXUS 870IS RAW Noise test

All looking good - we have quite a few edge artefacts with the JPEG and it is a bit hazy though the camera sharpening is pulling a lot of detail out. The lens seems to be the biggest factor influencing quality here and the camera sharpening is compensating for it much better - it may even have been tuned specifically for the lens on the camera. The camera sharpening may even be a bit too aggressive in places as it has an almost unreal "sharper than real life" character.

Noise reduction is hitting the textures, especially in the shadows but there is no sign of noise. Neatimage is keeping things particularly smooth with slightly more loss of texture but less artefacts than the JPEG.

With the RAW original, noise is already quite bad in the shadow areas, particularly colour noise.

ISO100

IXUS 870IS RAW Noise test

Not surprisingly, almost identical to the ISO100 tests though slightly more noise on the Camera JPEG and the RAW original.

ISO200

IXUS 870IS RAW Noise test

A more marked change - The Camera JPEG is getting more hazy and Neatimage is starting to smooth out textures leaving only the lines which is starting to look a little unnatural. Neatimage is also producing a very slight haze now, but the Camera JPEG seems to be doing a very good job of hanging onto texture.

With the RAW original the noise is now becoming obvious in the mid tones, and is clearly the least hazy.

ISO400

IXUS 870IS RAW Noise test

The haze is now really moving in with the Camera JPEG and the texture is being lost in the haze and a lot more artefacts becoming visible. Neatimage is still holding off the haze, however starting to get more ugly on the loss of texture leaving lines and undulations behind.

Neatimage has many adjustments so to some extent it can probably do better here simply by letting through more noise which will make the loss of texture less obvious.

ISO800

IXUS 870IS RAW Noise test

Surprisingly little change with the Camera JPEG and RAW via Neatimage though we are starting to see couloured blotches where the colour noise can't be effectively removed. The main thing is that the camera is producing more artefacts and Neatimage is letting through slightly more noise in the shadows.

The RAW original is getting decidedly ugly now and possibly also demosaicing artefacts making things look even worse.

ISO1600

IXUS 870IS RAW Noise test

It's a wonder that small sensors can even do this, but it's obvious that they are struggling.

The Camera JPEG is decidedly hazy, dull and has loads of artefacts and no texture. Really, quite horrible and with the course artefacts not going to print nicely.

Neatimage is doing an extraordinary job in comparison - the haze is held off and artefacts are evenly distributed and fine so less likely to show up badly on prints. Enough of the texture gone to have reduced the unnatural effect that we where seeing before and with more noise showing through this helps compensate for the loss of texture. Perhaps less aggressive settings would help with the mid-ISO values.

What Neatimage does seem to be struggling with is colour noise, particularly in the shadows where blotches of magenta and green are coming out of balance. This looks worse due to the lack of texture.

The RAW original is clearly very bad and shows what an astonishing job the noise reduction algorithms are actually capable of.

Conclusions and Thoughts

I'm surprised just how well noise reduction is managing to clean up the image from a small sensor. That said, there is really no comparison to what a large sensor in a dSLR does. Far more texture and detail is possible, and with a good lens (one of my SLR lenses costs about 15x what this whole camera cost me on eBay so an unfair comparison) there is really no substitute for serious kit.

Where the small sensor really falls down is in the shadow areas where detail is being badly hit by the noise and subsequent noise reduction. A highly acclaimed photographer once pointed out to me that with the move to digital, shallow depth of field had become fasionable as that was what everyone was being forced to do without camera movements they would previously have had on a view camera. To put it another way, artistic freedom is being restricted by the equipment. I have to wonder if the same is true with smaller sensors and digital in general - take a look at older photography like Ansell Adams where extensive use is made of shadow areas, or even just pre-digital classic journalism and it does appear that popular modern photography has gone higher key with far less shadow.

Neatimage could probably do much better with a little tuning at mid ISO settings. It is tending to remove all texture and this is making things look quite unnatural. Less aggressive settings may let through enough noise to compensate hide the texture loss. Colour noise does still need to be completely suppressed - it is particularly nasty and obvious even at low levels.

It's important to remember that this is not an entirely fair and scientific test. Without being able to apply exactly the same colour processing, curves, sharpening etc. we can't make conclusive comparisons.

Comments:

Johan Thole Image  14/03/2013 08:30 :: Johan Thole

I am positively surprised at the quality of the in-camera JPEGs for ISO200 and lower. Maybe there is a bit oversharpening, but RAW / Neatimage don't seem to bring out much more details than the DIGIC JPEG processing in the camera does. For higher ISOs the route is obvious; shoot RAW to keep control yourself.




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