Olympus C-700UZ Review: 17. Compared to...: Digital Photography Review

Compared to... (contd.)

Colour Chart Comparison

Now we can compare the C-700UZ to a couple of other cameras, using samples from our test archives we will now compare its image quality (colour and resolution) to the Canon PowerShot A20, Sony MVC-CD200 and Nikon Coolpix 950.

Colour charts are shot in daylight, Auto White Balance, EV compensation +0.3 (all cameras), measured light ~10 EV. This test is also dependent on the accuracy of the camera's auto white balance, the colour charts are shot in daylight but some camera's white balance is better than others. All cameras are given 20 seconds to "settle" before the shot is taken.


Olympus C-700UZ	Canon PowerShot A20

Sony MVC-CD200	Nikon Coolpix 950

In the table below we're only measuring colour. The RGB values were measured from a VGA reduced image (to average colours, remove noise and eliminate JPEG artifacts) using the Eyedropper tool in Photoshop with a 5 by 5 Average Sample Size.

Patch	Olympus C-700 UZ	Canon PowerShot A20	Sony MVC-CD200	Nikon Coolpix 950
Black	21,25,25	16,17,17	28,24,27	20,20,20
Black
Middle Gray	94,104,109	88,91,90	86,98,102	105,108,108
Middle Gray
White	194,204,210	204,206,203	184,198,196	198,198,198
White
Magenta	173,50,115	194,33,98	196,17,118	208,44,122
Magenta
Red	173,24,24	189,22,29	192,7,23	215,31,41
Red
Yellow	179,180,14	199,185,25	180,189,22	203,185,77
Yellow
Green	32,130,51	18,125,59	0,164,37	0,148,67
Green
Cyan	43,174,225	26,146,200	0,186,189	39,170,204
Cyan
Blue	33,51,130	23,27,86	57,31,148	57,51,132
Blue

The C-700 UZ does well, overall colours are good, an even balance across the board. As we spotted on the previous page greens have a slight yellow taint (though no more in % terms than other digital's).

Red Channel Noise

Something we've commented on previously is noise in the red colour channel in what should be pure blues. 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.

Blues are definitely better (more saturated) than the Canon A20, however they do seem to contain a fair amount of noise in the red channel.

Resolution Comparison

Shots here are of the PIMA/ISO 12233 standard resolution test chart (more of which are available in our comparison database). This resolution chart allows us to measure the actual performance of the lens and sensor system, it measures the ability of the camera to resolve lines at gradually higher resolutions and enables us to provide a definitive value for comparison purposes. Values on the chart are 1/100^th lines per picture height. So a value of 8 equates to 800 lines per picture height.

Studio light, cameras set to auto, all settings factory default. Exposure compensation +0.7 EV for all cameras.


Olympus C-700 UZ

Canon PowerShot A20

Sony MVC-CD200

Nikon Coolpix 950

Measurable findings (three measurements taken for each camera):

Camera	Measurement	Absolute Res.	Extinction Res.
Olympus C-700 UZ	Horiz LPH *	800	1000
	Vert LPH *	800	1050
	5° Diagonal LPH *	700	900
Canon PowerShot A20	Horiz LPH *	820	1000
	Vert LPH	800	1050
	5° Diagonal LPH	800	900
Sony MVC-CD200	Horiz LPH *	850	1050
	Vert LPH	850	1050
	5° Diagonal LPH	800	900
Nikon Coolpix 950	Horiz LPH	750	1050
	Vert LPH	750	1050
	5° Diagonal LPH	800	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.

The moiré effect on the C-700 UZ resolution charts is probably the worse I've seen, not a performance I'd expect of a second generation 2 megapixel and certainly not in line with other (even lesser priced) 2 megapixels. Resolution is better than the two year old Coolpix 950 but less than the A20 and CD200, probably what we'd expect of a complex 10x optical zoom.

If you take a closer look at the resolution charts it's also worth noting that the lens exhibits a certain amount of softness in the corners.

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