Compared to... (contd.)

Here we will use our standard color and resolution charts to compare the Pentax Optio S to the Canon PowerShot SD100 (Digital IXUS II), Casio EXILIM EX-Z3 and Nikon Coolpix SQ. Note that both the Pentax Optio S and Casio EXILIM EX-Z3 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, Canon & Nikon +0.3 EV compen. / Pentax & Casio +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).

Pentax Optio S Canon PowerShot SD100
Casio EXILIM EX-Z3 Nikon Coolpix SQ

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.


Optio S

PowerShot SD100


Coolpix SQ
Black 23,24,26 24,26,25 26,26,27 39,40,40
Middle Gray 101,102,108 104,106,107 109,109,108 113,110,112
White 201,202,206 215,217,216 213,214,209 222,217,218
Magenta 186,21,99 217,48,118 218,70,109 219,49,122
Red 189,8,29 208,41,44 220,56,44 204,39,37
Yellow 214,194,62 210,203,29 221,201,68 195,206,63
Green 37,133,78 7,145,81 40,134,68 31,158,84
Cyan 25,148,196 15,159,228 22,167,188 74,170,235
Blue 42,38,103 43,48,113 42,42,98 49,56,137

The Optio S always tended towards a cooler white balance in this test, although we repeated the shot several times we got pretty much the same results each time. You can see this in the slightly higher blue channel levels for the black, gray and white patches. Overall color response was quite similar to the Nikon Coolpix SQ with slightly less saturated blues and a cleaner yellow (from the S).

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.
Pentax Optio S (1,754 KB)
Canon PowerShot SD100 (1,210 KB)
Casio EXILIM EX-Z3 (1,589 KB)
Nikon Coolpix SQ (1,330 KB)

Measurable findings (three measurements taken for each camera)

Camera Measurement Absolute Res. Extinction Res.
Pentax Optio S 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 
Casio EXILIM EX-Z3 Horizontal LPH 1000  * 1250 
Vertical LPH 950  * 1200 
5° Diagonal LPH 900  n/a 
Nikon Coolpix SQ Horizontal LPH 1100  * 1350 
Vertical LPH 1000  * 1350 
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.

The Optio S produced about average results for a three megapixel digital camera, it probably lost out a little due to lens softness and image processing. As expected measured resolution was the same as the EXILIM EX-Z3, they both use the same lens and CCD combination.