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" on the CCD's signal amplifiers. Nothing is without its price however and doing so also amplifies any noise and can also affect colour saturation.

The Sony DSC-V1 provides five ISO sensitivities of ISO 100, 200, 400 and 800. It is the only one of the three cameras tested together (DSC-V1, Canon G5, Nikon 5400) which provides the sensitivity of ISO 800 equiv. (although if you look at the exposure table below you can see that the G5's ISO 400 is pretty close).

Our noise comparison test involves shooting a GretagMacBeth ColorChecker at a selection of ISO sensitivities and then measuring luminance and RGB noise at a 'mid' grey patch (patch 22).

What is the real sensitivity?

As you can see from the table below the Canon PowerShot G5 is approximately 0.7 EV (3/4 stop) more sensitive than both the Nikon Coolpix 5400 and Sony DSC-V1 at the same ISO setting. Note that the Canon and Nikon's range of sensitivities are ISO 50 - 400, the Sony ISO 100 - 800. Thus in effect the Canon's range of sensitivities is approximately equivalent to ISO 80 - 640 (compared to the other two cameras here).

Canon PowerShot G5 vs. Nikon Coolpix 5400 vs. Sony DSC-V1

Sample crops shown below are arranged in alphabetical order only (Canon, Nikon, Sony). Note that at higher sensitivities where noise is more visible some of the artifacts visible will be due to JPEG compression, it would be possible to remove these by shooting in RAW or TIFF modes but we prefer to use JPEG as it is more representative of typical use.

Camera settings / test notes

• All cameras were set to aperture priority (F5.0 or as near as possible)
• All cameras used manual white balance measured from a gray card
• All cameras exposure compensation was set to produce the same image histogram*
• All other image parameters (sharpening etc.) were set to normal (neutral setting)
• Image format used was full resolution, highest quality JPEG
• Sample images shot at approximately 21°C (~70°F)
• Lighting was daylight

* In fact the only adjustment required was the Nikon Coolpix 5400 with -0.3 EV

	ISO 50
	Canon G5 1/40 sec, F5.0	Nikon Coolpix 5400 1/29 sec, F4.7	Sony DSC-V1 -
Original
Red ch.
Green ch.
Blue ch.
	ISO 100
	Canon G5 1/80 sec, F5.0	Nikon Coolpix 5400 1/51 sec, F4.7	Sony DSC-V1 1/50 sec, F5.0
Original
Red ch.
Green ch.
Blue ch.
	ISO 200
	Canon G5 1/160 sec, F5.0	Nikon Coolpix 5400 1/110 sec, F4.7	Sony DSC-V1 1/100 sec, F5.0
Original
Red ch.
Green ch.
Blue ch.
	ISO 400
	Canon G5 1/250 sec, F5.0	Nikon Coolpix 5400 1/204 sec, F4.7	Sony DSC-V1 1/160 sec, F5.0
Original
Red ch.
Green ch.
Blue ch.
	ISO 800
	Canon G5 -	Nikon Coolpix 5400 -	Sony DSC-V1 1/320 sec, F5.0
Original
Red ch.
Green ch.
Blue ch.

A quick glance at the noise comparison graph below relates very closely to what we can see on the patches. That is that Sony's DSC-V1 exhibits the least noise of all the cameras, the Coolpix 5400 is next best and the G5 (even shifted to compensate for its extra sensitivity) has the most noise of the three (from ISO 100 upwards). I was quite surprised to see this, clearly the competition have caught and overtaken Canon in this respect.

One thing that's quite noticeable looking at the full color crops above is that Sony keep color balance under control throughout the sensitivity range, the Nikon crops for instance get progressively more color noise (cyan in this case) the higher up the sensitivity range.

Luminance noise graph

ISO sensitivity is on the horizontal axis of this graph, standard deviation (average) is on the vertical axis. Note that we have overlaid a 'shifted' G5 graph which more closely represents the ACTUAL sensitivity of the camera.

RGB noise graph

ISO sensitivity is on the horizontal axis of this graph, standard deviation (average) is on the vertical axis.