Camera sensor noise profile of a Canon Powershot G12

I was recently reading the article The Truth about Digital ISO in Digital PhotoPro magazine, and decided to investigate the camera sensor noise profile of the Canon Powershot G12 I use for underwater photography.

Noise plays a big part in underwater photography. Available light levels are lower underwater,with less available the deeper you go. Knowing the noise performance of your camera allows you to push the ISO and get maximum performance.

I started looking at noise in the Canon Powershot series of cameras in my previous post Noise Comparison – Canon Powershot G11 vs G10.

There has been some recent talk on the web about “native ISO”, where the lower ISO of a camera is not necessarily the best for noise performance due to in-camera amplification methods. I have always thought the underwater photos taken with my Canon G12 at ISO160 were better than ISO80 or ISO100, and thought this might have been the effect of native ISO.

After reading the article The Truth about Digital ISO in Digital PhotoPro magazine, I decided to test my theory.

I setup the camera in manual mode, with a shutter speed of 1/60 sec, aperture of f2.8, and fixed white balance. A fixed white balance is required so the camera does not try and change the colour tints of the high ISO noise, giving you an incorrect result.

I placed a filter barrel and cap over the lens to block out all light, and shot a sequence of RAW images at different ISO settings from 80 to 3200.

File Size

The first interesting thing I noticed was the size of the RAW files.

canon g12 raw files

The size of the file increased as the ISO increased with more sensor noise. The ISO3200 RAW file is nearly twice the size of the ISO80 file.

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How to use the Canon G11 Control Dial in an Underwater Housing

For a while now I have been under the impression you could not use the Control Dial on the Canon Powershot G11 when it was mounted in an underwater housing, but a recent review by Lawrence Alex Wu reveals a little known secret.

I was reading Underwater Photography Magazine (No 55 Jul/Aug 2010), and a review of the Canon Powershot G11 by Lawrence Alex Wu describes a key shortcut that allows the photographer access to the Control Dial functionality while underwater.

Canon Powershot G11 inside wp-dc34 underwater housing

Out of the housing, rotating the G11 Control Dial next to the screen allows you to adjust settings that include:-

  • Aperture size in Aperture Priority Mode (AV)
  • Shutter speed in Shutter Priority Mode (Tv)
  • Metering Modes
  • Manual Focus
  • Brightness Exposure Compensation
  • Auto Exposure Bracketing

I often use the Canon WP-DC34 underwater housing with my G11 camera, but the problem is that once you close the housing you no longer have access to the control dial…. or so I thought….

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Noise Comparison – Canon Powershot G11 vs G10

After hearing of the Canon Powershot G11 noise improvement, I grabbed one while in Hong Kong and compared it to my G10.

I had been aware of the improved noise performance of the Canon Powershot G11 since October 2009, and thought this would be beneficial when shooting underwater where you need every bit of sensitivity you can get.

In Hong Kong on business I picked up a Canon G11 and compared it directly with my Canon G10. The results were better than I expected and show considerable improvement in noise levels.

Test Conditions

I setup the G10 and G11 next to each other on the window sill of my hotel room. Both cameras were set to the same settings at f5.0 and center weighted average.

Focusing on the same apartment block I took shots with ISO 80, 100, 200, 400, 800 and 1600 at focal lengths settings of 6.1mm and 25mm. (Due to the smaller sensor, the focal length multiplier of 4.8 gives 35 mm equivalent focal lengths of  29mm and 121mm.)

The images were compared in Adobe Lightroom.

Exposure Differences

The first thing I noticed was the G11 image was brighter than the G10 image. Analyzing the Histogram for the images, the G11 image is exposed 0.70EV to the right making it brighter.

Exposing the image more to the right is a smart idea as there is more image information in this area.

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Canon G10 Sharpness Experiment

I was looking through a few images the other day and noticed the RAW images from my Canon G10 looked less sharp than those taken with my Canon 750IS. I was a bit concerned as it had recently been repaired.

The reason for this did not occur to me at time , so I decided to do an experiment, which taught me a couple of interesting things about the camera.

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