ISO Sensitivity / Noise levels

ISO equivalence on a digital camera is the ability to increase the sensitivity of the sensor. This works by turning up the "volume" (gain) on the sensor's signal amplifiers (remember the sensor is an analogue device). By amplifying the signal you also amplify the noise which becomes more visible at higher ISO's. Many modern cameras also employ noise reduction and / or sharpness reduction at higher sensitivities.


To measure noise levels we take a sequence of images of a GretagMacBeth ColorChecker chart (controlled artificial daylight lighting). The exposure is matched to the ISO (i.e.. ISO 200, 1/200 sec for consistency of exposure between cameras). The image sequence is run through our own proprietary noise measurement tool (version 1.4 in this review). Click here for more information. (Note that noise values indicated on the graphs here can not be compared to those in other reviews.)

Sony DSC-H5 vs Canon PowerShot S3 IS

  Sony DSC-H5
ISO 80

Canon PowerShot S3 IS
ISO 80
Crops
  Sony DSC-H5
ISO 100 		Canon PowerShot S3 IS
ISO 100
Crops
  Sony DSC-H5
ISO 200 		Canon PowerShot S3 IS
ISO 200
Crops
  Sony DSC-H5
ISO 400 		Canon PowerShot S3 IS
ISO 400
Crops
  Sony DSC-H5
ISO 800 		Canon PowerShot S3 IS
ISO 800
Crops

With tiny, high pixel count chips noise is always going to be an issue, and to a large degree this is more a test of the effectiveness (both measurable and visible) of a camera's noise reduction system. Designers have to balance the desire to produce smooth, clean results with the need to retain as much detail as possible (if you blur away the noise, you blur away image detail too).

These crops show clearly that Sony is using stronger noise reduction at higher ISO values (over ISO 200), but what is notable is that this results in cleaner results without losing significantly more detail than the Canon (especially if you do a little sharpening, and taking into account the extra resolution available in the first place). The ISO 200 result is remarkably good and the ISO 400 result is perfectly usable for smaller prints. ISO 800 is also just about usable for small prints, though the low noise comes at a price; the loss fine detail and some fairly obvious noise reduction artefacts.

Sony DSC-H5 vs DSC-H2 High ISO compared (ISO 400-1000)

  Sony DSC-H5
ISO 400 		Sony DSC-H2
ISO 400
Crops
  Sony DSC-H5
ISO 800 		Sony DSC-H2
ISO 800
Crops
  Sony DSC-H5
ISO 1000 		Sony DSC-H2
ISO 1000
Crops

At higher ISO settings there is a small but measurable difference in both the amount and appearance of noise and the noise reduction used. At settings of ISO 200 and over the stronger noise reduction needed by the 7MP chip used in the H5 more or less removes any resolution advantage. At ISO 800 and 1000 the H5 produces smoother looking results but they are softer too - and if you change settings (or apply post-processing) to sharpen up the H5 result you will see even less difference between these two cameras.

Luminance noise graph

Cameras compared:
Sony Cyber-shot DSC-H5, Canon PowerShot S3 IS, Panasonic DMC-FZ7
Note: ISO 50-1000 only (the FZ7's ISO 1600 mode is not shown).

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity is on the vertical axis.

As usual what we're really looking at here isn't 'noise' as much as noise reduction; all three cameras produce similar results at lower ISO settings, but the Panasonic has much heavier noise reduction at higher settings. The graph also clearly shows that the H5 has considerably lower measurable noise than the Canon S3 IS, particularly at higher ISO values, thanks to heavier noise reduction.

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 is on the vertical axis.

Like the H2 there is a fairly linear relationship between noise and ISO sensitivity, though at all but the highest ISO values the H5 has slightly higher noise.

Sony DSC-H2 and DSC-H5 compared

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of each of the red, green and blue channels is on the vertical axis.