Compared to... (contd.)

Colour Chart Comparison

Now we can compare the DiMAGE 7 to a few of other cameras. Using samples from our test archives, we will now compare its image quality to the Nikon Coolpix 995, Canon PowerShot G1 and Sony DSC-S85. I've thrown the 4 megapixel DSC-S85 in here as an 'upper end' expectation of resolution.

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.

As per other samples in this review the DiMAGE 7 image has been converted to the sRGB colour space using the Minolta Image Viewer application [info].

Minolta DiMAGE 7 (converted to sRGB) Sony DSC-S85
Fujifilm FinePix 6900Z Canon PowerShot G1
As I mentioned earlier in this review the DiMAGE 7 produces some of the nicest colour I've seen from any 'prosumer' level digital camera (once you've run the images through the Minolta Image Viewer). Some people may argue that the colour space conversion process is skewing these results, but at least Minolta have confirmed the DiMAGE 7's different colour space and provided a utility to convert it to a standard colour space (sRGB etc.).

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.




Fujifilm FinePix

Canon PowerShot
Black 29,30,32 17,17,19 37,32,31 34,32,34
Middle Gray 85,89,97 76,81,79 112,116,112 97,96,102
White 220,224,226 188,189,189 238,237,227 214,208,208
Magenta 212,40,116 170,12,124 254,27,119 204,41,121
Red 208,44,56 176,0,40 255,48,39 189,31,53
Yellow 215,221,45 181,180,14 253,211,46 205,193,59
Green 26,136,58 24,131,27 14,153,17 26,149,73
Cyan 22,144,215 23,158,175 0,174,231 58,180,230
Blue 45,31,104 23,31,112 33,39,126 55,49,117

Red Channel Noise

Something we noticed early on with the current crop of 3 megapixel cameras was a certain amount of noise in the red channel. 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.

As you can see there is some 'mottle effect' in the red channel for what should be a pure dark blue patch, however it's no more than you can see from the Fujifilm 6900Z or Coolpix 995. The cyan (light blue) patch is noticeably 'clean' in the red channel producing a nice pure colour.

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.

NOTE: Here I've also added the Olympus E-10 as many people have been comparing the two cameras.

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

Minolta DiMAGE 7
Sony DSC-S85
Olympus E-10
Fujifilm FinePix 6900Z
Canon PowerShot G1

Measurable findings (three measurements taken for each camera):

Camera Measurement Absolute Res. Extinction Res.
Minolta DiMAGE 7 Horiz LPH *1300  1450 
Vert LPH 1150  1450 
5o Diagonal LPH 900  n/a 
Sony DSC-S85 Horiz LPH 1200  1650 
Vert LPH 1150  1650 
5o Diagonal LPH 1000  n/a 
Olympus E-10 Horiz LPH 1150  1450 
Vert LPH 1100  1450 
5o Diagonal LPH 900  n/a
Fujifilm FinePix 6900Z Horiz LPH 1150 1400 
Vert LPH 1150  1450 
5o Diagonal LPH 900  n/a 
Canon PowerShot G1 Horiz LPH *950  1300 
Vert LPH *950  1400 
5o Diagonal LPH *900  n/a 

* Moiré is 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.

Here we can see that the DiMAGE 7's 5 megapixel CCD does manage to eek out a little more resolution, but it's not really what we'd expect. Comparing these results to Sony's DSC-S85 it's clear to see that it's not that different in its ability to resolve absolute detail. That said the DiMAGE 7 clearly produces more resolution than last years 3 megapixel digital cameras.

More Minolta DiMAGE 7 / Sony DSC-S85 resolution chart crops

Minolta DiMAGE 7 Sony DSC-S85

Note: with the later production unit and newer firmware the quality we're getting from the resolution chart shot is considerably improved, however this still doesn't seem to me to be everything we could expect from five megapixels nor does it look particularly good against the 4 megapixel DSC-S85.