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Compared to... (contd.)

Here we will use our standard color and resolution charts to compare the Canon PowerShot A70 to the Nikon Coolpix 3100, Canon PowerShot SD100 (Digital IXUS II) and Pentax Optio S. Note that the Pentax Optio S needed +0.7 EV exposure compensation (compared to our normal +0.3 EV) to accurately expose our standard color chart comparison (below).

Color Chart Comparison

Color charts are shot in daylight, Auto White Balance, all +0.3 EV compen. except Pentax with +0.7 EV compen. This test is also reliant on the accuracy of the camera's auto white balance, the color charts are shot in daylight but some camera's white balance is better than others. All cameras are given 20 seconds for their white balance systems to settle before the shot is taken (often we will take up to eight shots and select the 'average' AWB result).

Canon PowerShot A70 Nikon Coolpix 3100
Pentax Optio S Canon PowerShot SD100

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

Patch Canon
PowerShot A70

Nikon
Coolpix 3100

Pentax
Optio S

Canon
PowerShot SD100
Black 36,39,38 37,35,39 23,24,26 24,26,25
Middle Gray 99,102,102 110,107,109 101,102,108 104,106,107
White 212,212,209 235,225,230 201,202,206 215,217,216
Magenta 210,44,115 243,45,161 186,21,99 217,48,118
Red 203,37,47 230,40,72 189,8,29 208,41,44
Yellow 201,197,23 222,211,50 214,194,62 210,203,29
Green 6,141,76 20,154,56 37,133,78 7,145,81
Cyan 1,156,217 27,180,226 25,148,196 15,159,228
Blue 34,46,106 51,41,133 42,38,103 43,48,113

As you can see the two Canon's deliver very similar color response, and so they should as they are both based on Canon's DiGiC image processor. The A70's color is quiet neutral and well balanced. The Coolpix 3100 has as stronger color response, and once again the magenta color provokes a strong response, if you look at the red values for the Red and Magenta patches you will note that they are very high, not clipping but not far away.

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 1/100th 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 (to compensate for the white background). Click on the camera name below the crops to download the full resolution chart (large JPEG's).

Horizontal resolution Vertical resolution 5 degree diagonal res.
Canon PowerShot A70 (1,196 KB)
Nikon Coolpix 3100 (815 KB)
Pentax Optio S (1,754 KB)
Canon PowerShot SD100 (1,210 KB)

Measurable findings (three measurements taken for each camera)

Camera Measurement Absolute Res. Extinction Res.
Canon PowerShot A70 Horizontal LPH 1100  1300 
Vertical LPH 1000  * 1300 
5° Diagonal LPH # 900  n/a 
Nikon Coolpix 3100 Horizontal LPH * 1100  * 1300 
Vertical LPH 1000  * 1300 
5° Diagonal LPH # 900  n/a 
Pentax Optio S Horizontal LPH 1000  * 1250 
Vertical LPH 950  * 1200 
5° Diagonal LPH # 900  n/a 
Casio EXILIM EX-Z3 Horizontal LPH 1000  * 1250 
Vertical LPH 950  * 1200 
5° Diagonal LPH 900  n/a 
Canon PowerShot SD100 Horizontal LPH 1100  1300 
Vertical LPH 1000  * 1300 
5° Diagonal LPH # 900  n/a 

* Moiré is visible, + Chart maximum, # Jagged diagonals

Definition of terms

LPH Lines per Picture Height (to allow for different aspect ratios the measurement is the same for horizontal and Vertical)
5° Diagonal Lines set at 5° 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.

Measured the Canon PowerShot A70 and Nikon Coolpix 3100 both had identical resolution, that said the Coolpix's detail from around 1000 LPH onwards suffers from quite visible red / blue moiré, this is not visible on the A70's chart. Another thing I wasn't happy to see on the 3100's chart were the strong white halo artifacts around the black detail.

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