Canon PowerShot G7

Resolution (8.09)
The Canon PowerShot G7, tied with the PowerShot A640 in the compact digital camera "megapixel race," has a whopping 10 megapixels. We tested the quality of the camera’s 1/1.8-inch CCD by photographing an industry standard resolution chart and loading the images into Imatest software. We tested the camera at different focal lengths and apertures and report the sharpest shot the camera produced, which was taken at 22mm with an aperture of f/4.0. 

Click to view high-resolution image

The 10-megapixel image above shows a sharp center but slightly blurry corners. The black triangles in the corners are a lighter shade than those in the center on the image, although they are all completely black on the original resolution chart hanging on the wall of our office. This discoloration is a bit disappointing, but the Canon G7 still captured quite a bit of detail.

Imatest determines how sharp an image is in terms of line widths per picture height (lw/ph). This measurement indicates how many black and white lines of equal thickness could theoretically cram across the image without blurring together. The G7 could fit 1903 lw/ph horizontally with 4.8 percent oversharpening and 1695 lw/ph vertically with 13.9 percent undersharpening. This is quite impressive, as it should be for a camera that advertises 10 megapixels. The cheaper PowerShot A640 also advertises 10 megapixels and produces similar results, although it does so by applying more in-camera sharpening, which could cause artifacts and present problems when enlarging prints or editing the image on a computer. Between the two models, the G7 produces sharper images. 

Noise – Auto ISO (1.99)
After activating the automatic ISO setting, we tested the camera in optimal light to see how it would react. Many cameras choose a low ISO setting in this test, which the G7 did. However, even its low settings have at least 1 percent of the image speckled with noise. For this, the G7 received a disappointing 1.99 overall auto ISO noise score.

Noise – Manual ISO (5.06)
The Canon PowerShot G7 has an expansive manual ISO range, but it comes with a price. The higher the ISO sensitivity, the more noise will creep in the picture. Below is a chart that shows just how much noise (vertical axis) appears at each ISO setting (horizontal axis).

In terms of noise, the G7 performed much more like a compact camera - with a lot of pixels crammed on a small sensor - than a potential DSLR substitute. At the lowest ISO 80 setting, about 1 percent of the image consists of noise. This steadily climbs through ISO 400, then jumps way up. At ISO 800, about 2.5 percent of the image is speckled with noise and at ISO 1600 more than 5 percent of the image is lost to noise. Although there is less noise here than on the Canon A640, this still isn’t as clean as it should be.

Low Light (7.98)
We tested the Canon G7 in less perfect lighting by dimming our studio lights to 60, 30, 15, and 5 lux. The first two tests are done in fairly common lighting situations for most photographers. The latter two are dark enough that it sometimes takes some searching to find the shutter release; they are still useful in that these very dim tests illustrate the threshold and limitations of the imaging sensor.

Images remained illuminated and properly colored throughout the tests. Even at the dimmest 5 lux, the Canon G7 had a mean color error of 7.9. This is using the ISO 1600 setting. Compare that to the mean color error of 5.5 in perfect lighting with the low ISO 80 setting - not bad at all. The pictures are nicely colored and illuminated, but noise is visible across the frame.

Low Light Tests
60 Lux	30 Lux
15 Lux	5 Lux

There was some noise in optimal lighting, and noise is typically worse in darker situations. We tested this hypothesis and were surprised by the results. The longer the shutter was open, the less noise there was. Check out the following chart. It shows shutter speeds from 1-15 seconds on the horizontal plane and the accompanying noise on the vertical plane.

 

Most cameras show a steady slope upward, but the G7 shows a jagged line heading downward. It seems that the G7's long exposure noise reduction gets stronger as the exposure is prolonged. Of note, however, is the shutter speed range that isn’t as extensive as most cameras of this caliber. The Canon G7 slows to only 15 seconds whereas other models geared for enthusiasts top off at 30 or 60 seconds.

Despite the relatively short shutter speed range and presence of noise with the ISO 1600 setting, the Canon PowerShot G7 still delivered one of the best low light performances of a compact digital camera with the overall 7.98 score.

Dynamic Range (4.94)
To test how many shades of light to dark the camera can capture in one shot, we turned off the lights and backlit a film step chart that shows a series of rectangles ranging from transparent to black. The rectangles represent 13 exposure steps, which is more than what any digital camera can capture in a shot. We snapped pictures of the chart and uploaded them to Imatest, which determined how many exposure steps the G7 could capture at each ISO setting. As the ISO is increased, most cameras lose detail.

Indeed, the Canon PowerShot G7 lost a lot of detail and dynamic range as the ISO was increased. At its best, it captured a bit over 6 exposure steps. After ISO 200, the dynamic range plunged. At ISO 1600, only 2 exposure steps were captured. This is in optimal conditions too, so pictures may be quite dreary and lifeless at ISO 1600. The Canon PowerShot G7 did not perform well at all in terms of its dynamic range.

Speed/Timing
Startup to First Shot (8.1)
The Canon G7 took 1.9 seconds to power up and snap its first picture. It is always recommended that photographers anticipate the action and have cameras powered up beforehand because sometimes 1.9 seconds, although decent, is not fast enough to capture that perfect picture.

Shot-to-Shot (9.5)
In the Continuous mode the G7 took shots every 0.5 seconds and continued indefinitely. In Continuous AF mode the camera attempted to autofocus between shots and took pictures every 1.3 seconds until the card filled up. The Canon G7’s burst mode isn’t incredibly fast – it certainly won’t replace a DSLR – but it is decent for a compact model and its ability to continue to the memory card’s capacity is quite impressive.

Shutter-to-shot (9.0)
The auto focus isn’t DSLR-quality, so it takes the camera 0.6 seconds from the moment the shutter release is pressed to the moment the picture is taken in many cases. If the G7’s exposure and focus are already locked (the shutter is already pushed halfway down), then the shutter lag is only a few hundredths of a second.

Processing (8.2)
The G7 takes about 0.9 seconds to process one shot in all modes.