Standard Test charts

On this page we examine the conventional test charts you may be familiar with already. We continue to use these tests in conjunction with DXO Analyzer. Both sets of tests are very complementary.

Framing accuracy
It's all very well having a zillion megapixel camera, but if the camera only lets you frame a fraction of the actual scene being recorded, millions of those pixels can go to waste.


Above is the standard ISO test chart for electronic cameras as framed by our test camera. As you can see, the Casio Exilim Zoom EX-Z40 allowed us to frame the test chart almost perfectly, with a practically 100% view of the scene being recorded.

Resolution
The resolving power of a camera is important to understand in relation to sharpness. The ISO test target gives a good indication of the resolving power of a camera, which is affected by both the lens and the sensor as well as the image processing engine inside the camera.

Sharpness and resolution are not the same. An image can be less sharp than another but record the same amount of detail. Careful sharpening can clarify the detail and produce a better image, but sharpening cannot clarify detail that isn't there.

Below are two sections from a standard resolution chart taken by the Casio EX-Z40 and the same Fujifilm F440 we used for comparison purposes in the DXO Analyzer tests. The reason why the F440 selections look grainy is because they were taken using ISO 200 instead of 100 as we normally would.


Casio Exilim Zoom EX-Z40, ISO 100, f/3.5. f=62mm (equiv zoom setting)

The detail is noticeably sharper than the F440 below, but if anything there is slightly less resolving power in the EX-Z40 with the EX-Z40 running out of definition at just after the 13 mark and the F440 practically making it to 14.


Fujifilm FinePix F440, ISO 200, f/4.1, f=82mm (equiv zoom setting)

The F440 has a slight (half a stop) advantage at f/4.1 over the EX-Z40 (a smaller aperture can help resolution up to a point), but this is kind of balanced by the extra noise in the image because of the ISO 200 setting.


Casio Exilim Zoom EX-Z40, ISO 100, f/3.5. f=62mm (equiv zoom setting)

The slight diagonal patterning in the three central regions above shows aliasing issues have begun to make themselves felt. This is a probable sign of over-sharpening compared to the relatively clean performance of the F440 below.


Fujifilm FinePix F440, ISO 200, f/4.1, f=82mm (equiv zoom setting)

Although the EX-Z40 is 'sharper', the F440 resolves slightly more detail and is relatively free of unsightly digital artefacts.

Colour chart
Currently we use a Gretag Macbeth ColorChecker DC chart to evaluate digital camera colour quality. The target is lit using a custom-built daylight colour temperature lighting system. Special Solux tungsten halogen dichroic reflector lamps are used, over-driven by a custom-made DC power supply to generate an even 'hotter' colour temperature (which means a 'colder' white balance) than their 4700 Kelvin rating at 12V.

Special patented Solux dichroic lamps are designed to lose unwanted UV and infra red out the back of the lamp through the semi-reflective reflector. Combined with our over-drive power supply, the actual illumination on the test target is particularly close to natural sunlight, with a well-matched colour spectrum, especially compared to so-called fluorescent daylight lamps that exhibit spikes across the colour spectrum.

Our lighting rig means cameras can operate normally in auto white balance for the purposes of evaluating colour rendition under consistent and relatively authentic sunny day light illumination emulation, something that would be impossible with the fickle nature of the British weather!


Casio Exilim EX-Z40

The Casio EX-Z40 has a noticeably cooler colour balance than the Fujifilm F440 below. But the white and grey patches are very neutral. Casio has certainly resisted the temptation to over-saturate colours, a trick that proves too tempting for a lot of manufacturers of consumer digital cameras.

Fujifilm FinePix F440

By comparison, the F440's colours are decidedly on the warm side, with pronounced yellows and almost orangey reds.

Dayglo fluorescent colours
We've been doing this test for a while now. Fluorescent cards are photographed under the same daylight rig as the ColorChecker DC chart (above). Fluorescent colours are particularly difficult for digital cameras to reproduce.

Casio Exilim EX-Z40

The EX-Z40 fares little better (above) than most of its rivals, with rather washed out results, especially the yellow.

Fujifilm FinePix F440

While the F440 has more saturated orange, red and green hues, the yellow is even flatter than the EX-Z40.

White balance
Here we test the ability of the camera to cope with low levels of artificial light without using flash. Both a standard 60W soft white light bulb and an equivalent brightness low energy fluorescent replacement lamp are used fitted in a holder with a small white reflector, mounted about 100cm over the test scene, comprising some colourful ornaments and the ColorChecker DC chart against a white background. Shots are taken with the camera's white balance set to auto for both types of light source and for respectively matching preset white balance settings.

We are not comparing the EX-Z40 with another camera for this test.


Fluorescent light source with camera auto white balance set. This is a very good result for the EX-Z40, with near neutral greys and whites. The test image is underexposed, though.


Fluorescent light source with in-camera fluorescent tube white balance preset option selected. The spectrums of different fluorescent light sources vary considerably. Only one preset for fluorescent light is offered by the EX-Z40 and it did not match our light source at all well.


Tungsten filament (ordinary light bulb) light source with camera auto white balance selected. The image is under exposed, but it's reasonably neutral, though some warmth lingers.


Tungsten filament (ordinary light bulb) light source with camera tungsten white balance preset selected. Apart from the image being too dark, colour balance is practically neutral.

Macro (close) focus coverage
For the first time we are using a new test target we developed specifically for this test. It is designed to show the minimum area that can fill the frame, in square cm, at closest focus. The 1cm squares (black and grey) also show curvilinear distortion if present. We try to test the camera at fullest wide zoom setting, mid-zoom and full-tele, though not all cameras permit zooming in macro mode.


Wide zoom
Barrel distortion is evident and lateral coverage of 5cm is a respectable, but not spectacular.


Mid zoom
It is not possible to zoom to full tele with the EX-Z40 in macro mode. However, the mid-zoom setting provides much better close coverage than the wide zoom setting and with a lot less barrel distortion. Filling the frame with as little as 3.3cm across is a good performance and the end of the lens isn't inconveniently close to the subject either.