Color (7.91)
For those photographers who want to snap a shot of the blossoming dogwood in the backyard and have it turn out with proper colors, we tested the Canon A620’s color rendering capabilities. This PowerShot uses a Digic II image processor, which has traditionally wrought great scores in other Canon models. To be thorough, we tested the A620 by capturing a sequence of images of a GretagMacbeth color chart. This chart is used by many industry professionals and manufacturers to standardize what greens and reds and so forth should look like. The chart is made up of 24 tiles with various colors; it is modified below by Imatest imaging software to show the differences between the original chart and the way the Canon PowerShot A620 reproduces it. The inner vertical rectangle of each tile shows the true ideal color of the original GretagMacbeth chart. The outer square displays the color depicted by the Canon A620 and the inner square shows the ideal tones, corrected by the software for luminance.
Imatest also produced a more quantitative chart below. The variance in each color tile is shown by two shapes and connected by a line that shows the degree of error. The square represents the ideal color from the original GretagMacbeth chart. The circle shows the color produced by the Canon PowerShot A620.
Unfortunately, the Canon PowerShot A620 didn’t perform nearly as well as its predecessor, the highly popular Canon A520. The old A520 produced a 9.65 overall color score, while the A620 squeaked by with a 7.91 score. The charts from the two cameras look rather similar though. Both models exaggerate the red colors (#9 and #15) way too much, the green #4 quite a bit, and the blues just a touch too much (#8 and #13). The Canon A620 just exaggerated each color a little more so. This PowerShot digital camera has a 6.16 mean color error and over-saturated by 10.4 percent. In the end, these results won’t produce an orange dogwood tree but will embellish its foliage and make the grass a little greener in the picture than what is actually there.
Still Life Scene
Below is a shot of our still life scene captured with the Canon PowerShot A620.
Click on the image above to view the full resolution version.
Resolution / Sharpness (3.89)
One of the A620’s major improvements over its predecessor is its resolution. The Canon A520 had only 4 megapixels, while the A620 carries 7.1 effective megapixels. The newer model also has a larger image sensor at 1/1.8 inches. To test how effective the A620’s sensor is, we snapped several shots of the Industry Standards Organization 12233 resolution chart. We uploaded the shots into Imatest imaging software, which performed a bit of math for us and determined the resolution of the uploaded files.
The results are output as line widths per picture height (lw/ph), which is a theoretical measurement of how many alternating black and white lines one could cram into the A620’s frame before the camera started blurring them together. lw/ph is a similar measurement to the more traditional lp/ph, but takes the size of the recording media (sensor) into account.
Click on the image above to view the full resolution shot.
The sharpest image is shown above; it was captured with a 21.7 mm focal length and an aperture of f/4, using an ISO 50 setting. Horizontally, the Canon PowerShot A620 read 1708 lw/ph and over-sharpened by 20.7 percent. The shorter vertical plane performed even better with 1787 lw/ph resolved and only 2.34 percent over-sharpening. These figures are right on par with other compact models. In fact the Canon PowerShot S80, which advertises 8 megapixels, resolved 1633 lw/ph horizontally and 1809 lw/ph vertically. For its decent performance, the Canon PowerShot A620 received a 3.89 overall resolution score.
Noise - Auto ISO (5.58)
The Canon PowerShot A620 has an automatic ISO setting that we tested for metering accuracy and resulting noise. In optimal lighting conditions, the camera selected an appropriate ISO setting and produced relatively low noise. In fact, it produced about as much noise as it would have if the ISO was manually set to ISO 60 – which is not much at all. This result earns the Canon A620 a respectable 5.58 overall automatic ISO noise score. While this is great compared to other compact digital cameras, it is still below the 6.76 mark earned by the Canon A520.
Noise - Manual ISO (4.03)
For those more adventurous photographers interested in the A620 for its manually functionality, we tested the camera at each of its available ISO settings: 50, 100, 200, and 400. This range was once the standard for compact digital cameras, but is now becoming outdated as new models add high sensitivity to their offerings.
We tested the noise levels at each manual ISO setting and plugged the results into a regression analysis for the overall score. The chart below shows the individual results, with the ISO settings on the horizontal axis and the noise levels plotted on the vertical axis.
The rise in noise climbs steadily; this is good news. While noise always accompanies higher sensitivities - due to the increased amplification of the signal - some compact models jump to exorbitant amounts of noise in the ISO 400 setting. This isn’t the case with the Canon PowerShot A620. Noise is kept under control and handled even better than the A520. The old model had a similar rise in noise, but has more noise at each ISO setting. The larger image sensor on the Canon A620 likely contributed to the improved 4.03 overall manual ISO noise score.
Low Light Performance (6.5)
Since many photo opportunities often arise when the sun goes to sleep, we tested the A620 in low light. We tested it at four different light levels of 60, 30, 15, and 5 lux to determine how well the camera would perform in these common situations. Imagine a small living room with the shades drawn just after dark and two table lamps lighting the room softly; this is approximately 60 lux. Now imagine a single 40-watt bulb for the 30 lux equivalent. The 15 and 5 lux tests are roughly equivalent to the light in the dresser drawer, which we realize is uncommonly dark. However, we test at these extremely dim conditions to assess the efficiency of the image sensor and processor and indicate how the camera might perform in a dark club without the use of a flash.
The Canon PowerShot A620 has shutter speeds that go as slow as 15 seconds. For these tests, the A620 was placed on a tripod, set to ISO 400, and the flash was turned off.
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60 Lux
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30 Lux
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15 Lux
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5 Lux
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Comparisons between the A520’s low light shots and the A620’s pictures will tell all. The older A520 produced a black frame at 5 lux and didn’t perform much better in the other dimly lit tests. The Canon PowerShot A620 shows vast improvements with fully illuminated pictures and only slight discoloration. It also improves on the handling of noise at these low light levels. Below is a chart showing the shutter speed the camera chose on the horizontal axis and the corresponding noise level on the vertical axis.
The Canon PowerShot A620 kept its noise at the darkest light level and 5-second exposure lower than even the Canon S80’s brightest 1-second exposure. Overall, the Canon PowerShot A620 produced excellent images in low light and handled noise better than most digital cameras. For its valiant effort, the A620 received an overall 6.5 low light score.
Dynamic Range (5.5)
Dynamic range measures the span from the brightest to the darkest subject that a camera can record with detail in a single exposure. When the subject exceeds the dynamic range of the camera, the brightest parts of the subject are pure white, with no detail, or the darkest parts are pure black, or both the brightest and darkest areas are pure white or black.
We measure dynamic range with a standardized test. We photograph a step chart of rectangles graduated from very bright to very dark, and run the images through Imatest software, which analyzes the image to see how many steps the camera records at various quality levels. The test is designed to show the maximum dynamic range the camera can record. It's unlikely that any camera will perform as well shooting images of normal scenes. The results are useful for comparing cameras.
The A620 shows a typical result: at its lowest ISO setting, 50, the A620 picks up 10.6 stops of dynamic range at Imatest's Low Quality, and 6.6 stops at High Quality – good scores that indicate the camera can handle dynamic range well at that setting. The chart shows a significant decline at higher ISOs however. At 400, the A620's range drops to 8.05 stops in Low Quality and 3.24 in High Quality. These scores are lower than some competing cameras, and comparable to the scores other cameras get at ISO 1600. This result is particularly limiting, because 400 is an ISO setting that the user will need frequently in shade, shooting action in overcast conditions, and indoors – it's not like 1600, which most photographers regard as a special-purpose setting which entails penalty in quality.
Canon A620 - ISO50
Canon A620 - ISO400
Speed / Timing
Start-up (8.01)
The Canon PowerShot A620's lens telescopes out of the camera body each time the camera powers up, and it takes a little while. We got a shot off 2 seconds after hitting the power switch. Two seconds is a long time in candid shooting, so users should turn on the A620 before the action begins.
Shot to Shot (9.01)
The A620's burst mode shot 4 frames in just barely under 2 seconds, for a 2 frames-per-second burst rate. It took the A620 4 seconds to get ready to take another shot, and another three seconds to take a subsequent frame. This performance is not fast enough to shoot sports action sequences, though it might do just fine for children blowing out birthday candles. 2 frames per second is slow, but many users will be more frustrated by the fact that it only takes 4 shots at a time. Our testing was done on a 64MB Sandisk card, with NiMH AA batteries.
Shutter to Shot (8.2)
The A620 takes a large fraction of a second to focus. Our shutter-to-shot times that included focusing ranged from 0.3 to 0.5 seconds, depending on lighting and how easily the camera could focus on the subject. When the A620 was pre-focused, it got off shots in a quick 0.05 seconds.
