How to disable video gain on the Canon PowerShot SX1 camera

The Powershot SX1 is an amazing camera. I bought mine factory re-furbished, at a tremendous discount.

But it has a two frustrating gotchas. Both are its poor low light capability due to its small image sensor and lack of good signal processing to clean up the noise.

  • For stills, avoid shooting images above ISO 200 unless you have to; and then, only go to ISO 400. Anything above that is unusable. You can use third party software like Noise Ninja or NeatImage to really clean up camera noise, but would be nice to avoid that step. Never use the “Auto” mode in low light – it tries to turn dark into daylight. Instead, use P, Tv, Av or M modes. Set your ISO manually and/or set your own exposure settings.
  • Similarly, its low light video capability is positively awful and there is no way to override the camera’s automatic video exposure settings.

Or so we thought. Today I discovered a trick to affect the video gain setting.

For those of you who are still photographers, the ISO setting of your digital camera is equivalent to a video camera’s video gain. The higher the ISO number, the more amplification is added to the signal to try and pull an image out of darker scenes. Amplification occurs to both the useful signal – and the noise on the image sensor – such that increasing the amplification results in worse noise.

Professional video cameras and higher end consumer video cameras have a video gain setting to select, typically, video gain of 0 db to +18 db (some go as high as +36 db gain). The greater the number, the more gain or amplification you are adding to the signal and the noisier the image. But this means on real video cameras, you can disable gain (and the ugly noise) if you don’t want to have that.

Now for the trick. I have CHDK installed on my SX1 so the screen might show something different if you do not have CHDK running.

I pointed the camera out the window to where the sun was shining. I pressed the video record button. I then pressed the photo exposure button half way until the white focusing rectangle turns green (or yellow if you pressed the +/- exposure compensation button first). Continue to hold the exposure button half way down. This shows the ISO setting the camera has selected – for video.

Pan the camera into the interior of the room while continuing to hold the exposure button half way depressed. The room will remain dark and the ISO setting stays at 160 (or whatever it was for you).

Now, with the video still running, let go of the exposure button. The auto exposure feature kicks in and the ISO jumps to 400 and the room brightens up.

Therefore, the trick is to start your video clip at a bright area or light. Press video record. Then half depress the photo exposure button until the green rectangle appears. This locks the exposure and ISO setting (gain). Now, pan the camera into the area you want to video without so much awful noise caused by jumping to a high ISO (gain) setting.

Pretty cool, huh?

For interior shots, the SX1’s auto-only exposure mode tries to go to ISO 400 for everything. The total ISO video range is from ISO 80 up to a displayed 400. The ISO 400 setting is what shows in the display but I think its pushing out to about ISO 3200 when it goes full open. It is way too noisy and way to bright for ISO 400.

I found the best images occur with the ISO set to anything below 250. ISO 80 to ISO 125 is best, but its okay to 250. The next setting level is 320 and that starts getting pretty noisy at that point.

I ran across this by accident.  But it is a modified version of the exposure lock trick discovered on Canon’s HV20/HV30/HV40 camcorders. Same idea – point the camera at a brighter light and then invoke the exposure lock feature on the HV camera and you are good to go with video gain completely disabled. (On those cameras, you can also use the “Spotlight” mode, which disables video gain.)

Another trick that helps a little, and only a little, is the exposure compensation button in video mode. Start you video. Press the +/- button and it displays an exposure compensation setting bar (left to right) at lower left of viewer. Use the control wheel to reduce the exposure or increase the exposure. This affects the ISO but only a little.

Why didn’t Canon enable manual override of ISO, aperture and shutter speed? Certainly would have been possible. And might even be possible with CHDK if we can figure out what memory ports to poke with what values.

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