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On my camera, a Canon PowerShot G1X, I can select picture sizes from S to L.

Now I wondered, if I select a smaller picture size, that would theoretically lead to more sensor surface per pixel, possibly making the camera perform better in low-light or other 'harsh' conditions.

However, when I try this, I can't notice any difference in behaviour. The end result just looks like a resized version of the larger picture, and there are no differences in shutter speed and ISO to get to that result.

So, it looks like the camera just takes a large picture and then downscales it, which was against my expectations (or at least against my hopes).

Pixel Binning

The term that I think I am looking for is Binning also known as CCD Binning, Data Binning or Pixel Binning.

It certainly has advantages over downscaling by software, because it makes more efficient use of the hardware (faster reading, better noise reduction).

I think the answers below don't really answer my question. Neither do the answers of the supposedly 'duplicate' of this question, although the answer by mattdm came closest by at least suggesting that a camera might support this 'hardware-level binning', which allowed me to continue my search.

So far I couldn't find evidence that the Canon G1X supports binning, so I'm afraid it does not. But if someone know if it does (or maybe knows a hack or trick to enable it), please let me know. Previously I had a Canon PowerShot SII, and there was a way to install 3rd party firmware to unlock extra features. Maybe something like that is possible for the G1X as well?

  • G1X uses a CMOS sensor, not CCD and no, it doesn't support pixel binning. You aren't going to get noise reduction like you think you will. See: this ML discussion thread. The G1X does have a CHDK build, but I wouldn't expect this to be one of the features. – inkista Nov 18 '14 at 22:55
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I do not know your specific camera model, but I think in general that the S-to-L scale refers to the size of the compressed jpg image when stored on your camera memory card.

In other words, your camera takes a raw picture at most of its possibilities and then compresses it in jpg format to save space on disk. Jpg is a lossy format, it means you can compress more at the cost of losing some information compared to the original image.

When you choose S you lose more details but get smaller files for your photograph; when you select L you waste some space but get finer details.

Beware that, given today's technologies, you probably can notice the data loss on specific pictures (i.e. when there are very fine details) or at very high zoom level.

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    S-to-L scale does refer to resolution on this camera, options for compression ratio are Fine/Normal (manual pages 57-58). – Imre Nov 16 '14 at 17:22
  • I gave a look to your camera manual and I agree that "image resolution refers" to the size in pixel of the image, but I'm persuaded the principle is the same as per the compression factor: the camera shots the raw picture at most of its possibilities and then scales down to the size you selected. – Chosmos Nov 16 '14 at 20:53
  • Imre is right. S to L refers to the pixel dimensions of the image. Compression level (quality) is a different setting. – GolezTrol Nov 17 '14 at 8:25
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Your conclusion is partially correct.

You will get some noise reduction as part of the downscaling process. But it will come from the same image and camera settings (shutter, aperture, ISO) won't be different for the S and L modes.

It's also likely that the S mode is using a lower quality setting on the JPEG encoder, which will negate some of the gains you might make in noise reduction.

There are cameras like the Nokia pureview phone camera or some of the early Fuji DSLR's which benefit significantly from downscaling but are also specifically designed to do so.

If you wanted to try to replicate what you think the camera is doing you can dial in -1.0 EV of exposure compensation - that would affect how the shutter & aperture are set and underexpose it. You can then shoot in the highest resolution available and see if you get a better result by 'pushing' or lightening it in post-processing.

  • The last paragraph is not really clear to me and seems to come out of the blue. Could you maybe link to some text (maybe even another answer here) that explains the workings of this technique? Also: which would how the shutter It seems a word is missing, could you please edit it in? – Saaru Lindestøkke Nov 16 '14 at 14:49
  • I've tweaked the last para. The idea is simple, shoot for more light than your camera guesses at (it'll give you a darker image) and at full resolution. Then reduce the size to reduce the noise and lighten it in your favourite image editing program and see if the results are better. – James Snell Nov 16 '14 at 19:42
  • Exposing to the left will usually introduce more noise when you push the exposure in post because you are amplifying the noise as well as the signal. To reduce noise you need to ETTR (overexpose) and then pull the exposure in post. – Michael C Nov 17 '14 at 0:25
  • ETTR is only relevant for raw, though. The gamma applied to generate the jpeg's distributes the "bits" relatively evenly over the histogram. – ths Nov 17 '14 at 11:18
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There are many ways your camera might try to create a smaller image file, among them higher JPG compression. What exactly is going on inside of your camera is the manufacturer's secret.

My assumption would be that the camera takes a raw image as usual and then just downscales it using a cheap (in terms of processing cost) rescaling algorithm. This is usually nothing that you have any influence on. The resulting image might look slightly better but this is largely due to the noise reduction achieved via downscaling.

Because of this I usually avoid taking pictures at a resolution lower than the sensor resolution. Instead, I select the maximum resolution or, if possible, RAW format. Afterwards, you can then edit the picture on your computer and fine-tune the downscaling and compression options, maybe even apply some more noise reduction before producing the end result.

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    Thanks. Your advice is sound, and it's how I normally do it. But it was that "manufacturer's secret" I was asking about. :) I think I've found out what I meant (see the 'answer' addition to my question). – GolezTrol Nov 17 '14 at 21:37

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