Previous page Next page


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

HP Photosmart 935 vs. Canon PowerShot S50

The PowerShot S50 was approximately one stop faster than the HP 935 at the same indicated sensitivity. This means that the 935 set to ISO 200 has the same actual sensitivity as the S50 set to ISO 100.

  HP Photosmart 935
ISO 100
, 1/141 sec, F5.5
Canon PowerShot S50
ISO 50
, 1/125 sec, F5.0
 Partial crop
Red|Green|Blue
channels
  HP Photosmart 935
ISO 200
, 1/176 sec, F5.5
Canon PowerShot S50
ISO
100, 1/250 sec, F5.0
 Partial crop
Red|Green|Blue
channels
  HP Photosmart 935
ISO 400
, 1/341 sec, F5.5
Canon PowerShot S50
ISO 200, 1/400 sec, F5.0
 Partial crop
Red|Green|Blue
channels
  HP Photosmart 935
n/a
Canon PowerShot S50
ISO
400, 1/800 sec, F5.0
 Partial crop
Red|Green|Blue
channels

As you can see from the graph below the 935 has a slightly odd noise profile, noise at ISO 100 and 200 are virtually the same, visibly it would be fairly difficult to tell them apart. At ISO 400 the camera comes back in line with the Sony DSC-V1 and Canon S50. This could perhaps be due to differing levels of noise reduction at different sensitivities.

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 S50. Note that this graph also includes results from the Sony DSC-V1.

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 Sony DSC-V1.

Previous page Next page
0
I own it
0
I want it
1
I had it
Discuss in the forums

Comments