Sony DSC-S75 Review: 14. Compared to...: Digital Photography Review

Compared to... (contd.)

Colour Chart Comparison

Now we can compare the DSC-S75 to a couple of other cameras, using samples from our test archives we will now compare its image quality to the Sony DSC-S70, Nikon Coolpix 990 and Canon PowerShot G1. *U

Colour charts are shot in daylight, Auto White Balance, EV compensation +0.3 (all cameras), measured light ~10 EV.

Sony DSC-S75 Nikon Coolpix 990

Canon PowerShot G1 Sony DSC-S70

As you can see the S75 exhibits far better colour output than any of its 3 megapixel rivals, colours are cleaner and stronger far more accurate and better balanced, indeed you can see an improvement over last years S70, and we raved about its colour reproduction. Mostly it's about the purity of the colours and especially the strength of blues and greens. *U

We're only measuring colour here. RGB values below were taken from a VGA reduced image (to average colours and eliminate JPEG artifacts) using the Eyedropper tool in Photoshop with a 5 by 5 Average Sample Size.

	Sony DSC-S75	Nikon Coolpix 990	Canon PowerShot G1	Sony DSC-S70
Patch White	193,195,194	201,201,201	214,208,208	182,182,182
Patch White
Middle Gray	90,94,95	104,104,104	97,96,102	85,85,87
Middle Gray
Patch Red	205,0,26	223,52,58	186,33,53	189,17,27
Patch Red
Patch Green	34,138,34	5,149,63	26,149,73	1,132,35
Patch Green
Patch Blue	31,24,152	60,50,112	55,49,117	33,26,123
Patch Blue

Red Channel Noise

Something we noticed early on with the current crop of 3 megapixel cameras was a certain amount of noise in the red channel, even at normal shutter speeds. This was most visible in the light blue of skies or painted walls. Our colour patch test chart turned out to be a good "leveller" and a way to measure the performance of one camera to the next.

The samples below are of 40 x 40 blocks cropped from the colour comparison charts above of the Blue and Cyan patches, each block is then broken down into it's red green and blue channels and reflected as such directly below. *U

As you can see the S75 and S70 both have a little red in their blue channel (a little more so for the S75), therefore some visible "red channel noise" would be seen in any large blue areas of an image (such as blue sky, a common complaint) it's also worth noting the intensity and purity of the blue channel indicating a far cleaner and more saturated blue response (as we saw above).

UPDATE 25/May/2001: There seems to have been some debate on this issue on our Sony Talk forum as to the amount of visible red channel noise on the S75 compared to the S70. My only additional comment would be that the S75 does seem to boost colours a little more than the S70 did which would of course lead to more visible colour noise.

Resolution Comparison

Shots here are of the PIMA/ISO 12233 standard resolution test chart (more available for comparison in our comparison database). Studio light, cameras set to auto, Exposure compensation +0.7 EV for all cameras. How to read the charts: All values are 1/100 th lines/picture height/width. So the "10" value equates to 1000. *U

Sony DSC-S75

Nikon Coolpix 990

Canon PowerShot G1

Sony DSC-S70

Measurable findings (three measurements taken for each camera):

Camera	Measurement	Absolute Res.	Extinction Res.
Sony DSC-S75	Horiz LPH	1050	1400
	Vert LPH	1050	1500
	5^o Diagonal LPH	1000	n/a
Nikon Coolpix 990	Horiz LPH	900	1300
	Vert LPH	900	1400
	5^o Diagonal LPH	900	n/a
Canon PowerShot G1	Horiz LPH	950	1300
	Vert LPH	950	1400
	5^o Diagonal LPH	900	n/a
Sony DSC-S70	Horiz LPH	1050	1400
	Vert LPH	1050	1500
	5^o Diagonal LPH	1000	n/a

Definition of terms:

LPH	Lines per Picture Height (to allow for different aspect ratios the measurement is the same for horizontal and vertical)
5^o Diagonal	Lines set at 5^o diagonal
Absolute Resolution	Still defined detail (below Nyquist frequency*)
Extinction Resolution	Detail beyond camera's definition (becomes a solid gray alias)
n/a	Not Available (above the capability of the test chart)
n/v	Not Visible (not visible on test results)

* Nyquist frequency defined as the highest spatial frequency where the CCD can still faithfully record
image detail. Beyond the Nyquist frequency aliasing occurs.

As we'd expected, the S75 sits up their with it's older brother for absolute resolution, whatever Sony have in the combination of lens and image processing they've managed once more to produce some of the highest resolution we've seen on a 3 megapixel consumer digital camera, absolute resolution well into 1000 lph and detail only disappearing (extinction resolution) at around 1400 lph. *U

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