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Compared to... (contd.)

Colour Chart Comparison

Now we can compare the PowerShot A20 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 Digital IXUS 300 (S300 ELPH) , 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.

Canon PowerShot A20 Canon Digital IXUS 300
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 and eliminate JPEG artifacts) using the Eyedropper tool in Photoshop with a 5 by 5 Average Sample Size.

  Canon Powershot A20
Canon Digital
IXUS 300
Sony
MVC-CD200
 
Nikon
Coolpix 950
Patch White 206,206,202 211,213,210 184,198,196 198,198,198
       
Middle Gray 88,91,91 98,99,99 86,98,102 105,108,108
       
Patch Red 187,22,29 201,29,41 192,7,23 215,31,41
       
Patch Green 18,125,56 26,131,64 0,164,37 0,148,67
       
Patch Blue 24,27,86 25,30,93 57,31,148 57,51,132
       

As we saw with the IXUS 300 the A20 also exhibits "dull blues", otherwise colours are relatively accurate (especially for an "entry level" digital camera) and bright. White balance is also very good.

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.

The A20 exhibits good channel separation (colour purity) and even less noise in the red channel than we saw from the IXUS 300 (interesting). A commendable performance.

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, Exposure compensation +0.7 EV for all cameras.

Canon PowerShot A20
Canon Digital IXUS 300 (S300 ELPH)
Sony MVC-CD200
Nikon Coolpix 950

Measurable findings (three measurements taken for each camera):

Camera Measurement Absolute Res. Extinction Res.
Canon PowerShot A20 Horiz LPH * 820 1000
Vert LPH 800 1050
Diagonal LPH 800 900
Canon Digital IXUS 300 Horiz LPH * 820 1000
Vert LPH 800 1050
Diagonal LPH 800 900
Sony MVC-CD200 Horiz LPH * 850 1050
Vert LPH 850 1050
Diagonal LPH 800 900
Nikon Coolpix 950 Horiz LPH 750 1050
Vert LPH 750 1050
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)
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.

Despite the appearance of higher resolution in our previous comparison the A20 shows exactly the same resolution as the IXUS 300 (which is what we'd expect after all). The A20 also exhibts some moire pattern at higher frequencies, which although they didn't show up in any of our samples, should be considered. Resolution is along the lines of what we'd expect from a 2 megapixel digital camera.

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