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Compared to... (contd.)

Colour Chart Comparison

Now we'll use the data in our review database to compare the S40's colour and resolution to three other four megapixel digital cameras: the Olympus C-40Z, Canon PowerShot G2 and Sony DSC-S85.

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.

Canon PowerShot S40 Olympus C-40Z
Canon PowerShot G2 Sony DSC-S85

As we'd expect virtually identical performance as the G2. The G2's shot has a slight cyan cast, this could be put down to very slightly different ambient light when we took the shot, it's not that significant.

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 Canon
PowerShot S40
PowerShot G2
Black 30,30,30 30,31,29 45,43,42 17,17,19
Middle Gray 103,102,103 100,99,99 107,106,110 76,81,79
White 215,210,211 214,216,211 208,210,208 188,189,189
Magenta 199,41,113 208,51,116 196,37,116 170,12,124
Red 196,33,42 196,45,41 195,30,35 176,0,40
Yellow 211,192,38 206,207,50 205,195,20 181,180,14
Green 33,140,67 8,143,63 43,152,68 24,131,27
Cyan 26,160,223 17,155,224 23,169,234 23,158,175
Blue 33,44,116 49,48,111 61,56,133 23,31,112

Resolution Chart 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 1/100th 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.

Horizontal resolution Vertical resolution 5 degree diagonal res.
Canon PowerShot S40
Olympus C-40Z
Canon PowerShot G2
Sony DSC-S85

Measurable findings (three measurements taken for each camera):

Camera Measurement Absolute Res.  Extinction Res. 
Canon PowerShot S40 Horiz LPH 1250  *1400 
Vert LPH 1100  1400 
5o Diagonal LPH 1000  n/a 
Olympus C-40Z Horiz LPH *1200  *1350 
Vert LPH 1100  1400 
5o Diagonal LPH 1000  n/a 
Canon PowerShot G2 Horiz LPH 1250  *1450 
Vert LPH 1200  *1500 
5o Diagonal LPH 1000  n/a 
Sony DSC-S85 Horiz LPH 1250  *1650 
Vert LPH 1200  1650 
5o Diagonal LPH 1000  n/a 

* Some artifacts / moiré visible

Definition of terms:

LPH Lines per Picture Height (to allow for different aspect ratios the measurement is the same for horizontal and vertical)
5o Diagonal Lines set at 5o 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 S40 did remarkably well, especially considering its tiny lens. Resolution was virtually identical to the G2, perhaps a little less in the vertical direction. Where the G2's lens will perform better is corner sharpness (the S40 can be a little soft in the corners) and its relative speed (F2.0 - F2.5 vs. F2.8 - F4.9). Also putting up a good fight is Olympus's C-40Z, although it's a shame about all that moiré.

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