Sony DSC-F828 review: Page 14. Photographic tests [Digital Photography Review]

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.

How sensitive is the F828?

In our tests the DSC-F828 was approximately a third of a stop (0.3 EV) less sensitive than the DSC-F717 at the same selected ISO and approximately two thirds of a stop (0.7 EV) less sensitive than the Canon EOS-300D (Digital Rebel).

Thus ISO 200 on the DSC-F828 would be the same as ISO 160 on the Sony DSC-F717 (but that setting doesn't exist) or ISO 125 on the Canon EOS-300D.

Test notes

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

Sony DSC-F828 vs. Sony DSC-F717

	Sony DSC-F828 ISO 64, 1/60 sec, F3.5	Sony DSC-F717 n/a
Partial crop
Red Green Blue channels

	Sony DSC-F828 ISO 100, 1/80 sec, F3.5	Sony DSC-F717 ISO 100, 1/100 sec, F3.5
Partial crop
Red Green Blue channels

	Sony DSC-F828 ISO 200, 1/160 sec, F3.5	Sony DSC-F717 ISO 200, 1/200 sec, F3.5
Partial crop
Red Green Blue channels

	Sony DSC-F828 ISO 400, 1/320 sec, F3.5	Sony DSC-F717 ISO 400, 1/320 sec, F3.5
Partial crop
Red Green Blue channels

	Sony DSC-F828 ISO 800, 1/640 sec, F3.5	Sony DSC-F717 ISO 800, 1/640 sec, F3.5
Partial crop
Red Green Blue channels

Sony DSC-F828 vs. Canon EOS-300D

	Sony DSC-F828 ISO 64, 1/60 sec, F3.5	Canon EOS-300D n/a
Partial crop
Red Green Blue channels

	Sony DSC-F828 ISO 100, 1/80 sec, F3.5	Canon EOS-300D ISO 100, 1/100 sec, F4
Partial crop
Red Green Blue channels

	Sony DSC-F828 ISO 200, 1/160 sec, F3.5	Canon EOS-300D ISO 200, 1/200 sec, F4
Partial crop
Red Green Blue channels

	Sony DSC-F828 ISO 400, 1/320 sec, F3.5	Canon EOS-300D ISO 400, 1/400 sec, F4
Partial crop
Red Green Blue channels

	Sony DSC-F828 ISO 800, 1/640 sec, F3.5	Canon EOS-300D ISO 800, 1/800 sec,F4
Partial crop
Red Green Blue channels

As you can see visually from the patches above and from the data presented on the graphs below the DSC-F828's baseline noise level is higher than the five megapixel DSC-F717 it replaces. To many (me included) this doesn't come as very much of a surprise, the much smaller size of the DSC-F828's photosites means less sensitivity and more prone to noise. The DSC-F828's noise levels at ISO 64 are visually identical to the DSC-F717 at ISO 100. For reference purposes I also included patches / results from EOS-300D with its much larger six megapixel CMOS sensor.

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 DSC-F828's luminance noise measurement at ISO 800 was greater than 10 (the maximum of our graph).

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. Note that the DSC-F828's red noise measurement at ISO 800 was greater than 10 (the maximum of our graph).

Still life comparisons

Below you will find 100% crops from a scene shot with the DSC-F828 and DSC-F717 at each camera's lowest noise sensitivity (ISO 64 / 100) and also at ISO 400.

At full resolution - ISO 64 / 100

Sony DSC-F828 @ ISO 64 (1/20 sec, F5)	Sony DSC-F717 @ ISO 100 (1/30 sec, F5)

At full resolution - ISO 400

Sony DSC-F828 @ ISO 400 (1/125 sec, F5)	Sony DSC-F717 @ ISO 400 (1/125 sec, F5)

The effects of downsampling

The DSC-F828's noise grain appears to be large enough to be maintained by most downsampling algorithms. The crops below were created by downsampling (using Adobe Photoshop CS) the eight and five megapixel images from the DSC-F828 and DSC-F717 to 2.16 megapixels (a 6x4" print at 300 dpi) - effectively what a printer driver would do internally when generating a 6x4" print. We chose the small print size as a 'best case', larger print sizes would obviously leave noise more visible.