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ISO Sensitivity / Noise levels


Standard Test

ISO equivalence on a digital camera is the ability to increase the sensitivity of the sensor to enable faster shutter speeds and/or better performance in low light. The way this works in a digital camera is by "turning up the volume" (gain) on the CCD's signal amplifiers. Nothing is without its price however and doing so also typically increases visible noise (random speckles visible all over the image).

We are now using a more reliable, repeatable and neutral method for evaluating noise. Shots are taken in daylight lighting in our studio. Noise is measured as the standard deviation of the medium gray patch on a Gretag MacBeth ColorChecker chart. The image is normalized before measurement of noise to remove the possibility of figures being affected by image contrast (one method of masking noise). Note that noise numbers shown on the graphs below can not be compared to those in older reviews.

Test notes:

  • Shots taken at approximately 21°C (~70°F)
  • Lighting was simulated daylight
  • Manual white balance
  • Aperture Priority

Canon PowerShot S50 vs. Sony DSC-V1

Our previous experience of Canon's conservative rating of these sensitivities was born out in these tests. The PowerShot S50 was at least one stop faster than the DSC-V1 at the same indicated sensitivity. This means that the S50 set to ISO 100 is as sensitive as the DSC-V1 at ISO 200.

  Canon PowerShot S50
ISO 50
, 1/125 sec, F5.0
Sony DSC-V1
ISO 100
, 1/125 sec, F5.0
 Partial crop
Red|Green|Blue
channels
  Canon PowerShot S50
ISO 100
, 1/250 sec, F5.0
Sony DSC-V1
ISO 200
, 1/250 sec, F5.0
 Partial crop
Red|Green|Blue
channels
  Canon PowerShot S50
ISO 200
, 1/400 sec, F5.0
Sony DSC-V1
ISO 400, 1/500 sec, F5.0
 Partial crop
Red|Green|Blue
channels
  Canon PowerShot S50
ISO 400
, 1/800 sec, F5.0
Sony DSC-V1
ISO 800
, 1/800 sec, F5.0
 Partial crop
Red|Green|Blue
channels

When the 1/1.8" (7.2 x 5.3 mm) five megapixel CCD was first announced there was universal concern about levels of noise which would be produced from such small pixel cell sizes. While not quite as clean as some newer three megapixel digital cameras levels of noise exhibited certainly aren't higher than from previous four or five megapixel digital cameras. Taking into account the S50's higher than indicated sensitivity we can see from the graph below that it matches the Sony DSC-V1 all the way up the sensitivity range.

Luminance noise graph

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity (normalized) on the vertical axis. Note that the faint shifted line better represents the actual sensitivity of the Canon PowerShot S50. Note that this graph also includes results from the HP Photosmart 935.

RGB noise graph

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of each of the red, green and blue channels (normalized) are on the vertical axis. Remember that the S50 is in fact approximately one stop (ISO 50 -> 100, ISO 100 -> 200, etc.) more sensitive than is indicated. Note that this graph also includes results from the HP Photosmart 935.

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