Canon A640 Exposure

Saturation & Hue Accuracy
Slightly oversaturated color (especially reds and blues), very typical of consumer digital cameras. Generally good hue accuracy.

The other important part of color rendition is hue accuracy. Hue is "what color" the color is. Here, the A640 did quite well. Like most digicams, it shifts cyan colors toward blue, to produce better-looking sky colors, but the rest of the hues were reasonably accurate.

Exposure and White Balance

Indoors, incandescent lighting
Moderate cool cast with both Auto and Incandescent white balance settings.

Color balance indoors under both Auto and Incandescent lighting was just a bit cool, but pleasing. The Canon A640 required a +1.0 EV exposure compensation boost to get a good exposure. Overall color well-balanced and hue accurate. Again, quite good. Our test lighting for this shot is a mixture of 60 and 100 watt household incandescent bulb, a pretty yellow light source, but a very common one in typical home settings here in the U.S.

Outdoors, daylight
Good color balance, very bright colors. Better than average exposure accuracy.

Outdoor shots generally showed accurate exposure with less a tendency to blow out highlights than I'm used to seeing. Shadow detail also tended to hold up pretty well for a consumer digicam. Exposure accuracy overall was better than average, the camera requiring less exposure compensation than I'm accustomed to seeing with consumer digicams.

See full set of test images with explanations
See thumbnails of all test and gallery images

Resolution
High resolution, 1,450 lines of strong detail.

Our laboratory resolution chart revealed sharp, distinct line patterns down to about 1,450 lines per picture height, with extinction well beyond the 2,000 line limit of the chart. Use these numbers to compare with other cameras of similar resolution, or use them to see just what higher resolution can mean in terms of potential detail. Beware that while you might be able to make out what looks like distinct lines at numbers higher than those we've mentioned here, the camera is just doing its best to continue interpreting the lines. So the lines you see at 1,500 and higher are really only artifacts generated by the camera's imaging system.

See full set of test images with explanations
See thumbnails of all test and gallery images

Sharpness & Detail
Fairly sharp images, with some blurring of detail from noise suppression.

The Canon A640's images are reasonably sharp, without any strong over-sharpening or edge enhancement on the camera's part. (Edge enhancement creates the illusion of sharpness by enhancing colors and tones right at the edge of a rapid transition in color or tone.)

Noise-suppression systems in digital cameras tend to flatten-out detail in areas of subtle contrast. The effects can often be seen in shots of human hair, where the individual strands are lost and an almost "watercolor" look appears. The crop at far right shows this, with darker areas of Marti's hair showing only limited detail, even though individual strands are quite visible against her cheek in the uncropped image. (The level of detail loss shown here isn't all that obvious on prints 8x10 inches or smaller though.)

ISO & Noise Performance
Moderate noise at the normal sensitivity settings, very high noise that blurs detail at the higher settings.

The Canon A640's sensitivity ranges from ISO 80 to 800 equivalents. Up to ISO 200, the camera produced very little noise, with only slightly blurred detail in the dark areas. At ISO 400 and especially at 800, the noise level and the amount of blurring that results increased noticeably. Overall though, the Canon A640's noise levels are lower than average for its class.

Extremes: Sunlit and low light tests
High resolution with good overall detail, though high contrast and limited shadow detail. Pretty good low-light performance, capable of capturing bright images under average city street lighting and slightly darker conditions.

Sunlight:
Because digital cameras are more like slide film than negative film (in that they tend to have a more limited tonal range), we test them in the harshest situations to see how they handle scenes with bright highlights and dark shadows, as well as what kind of sensitivity they have in low light. The shot above is designed to mimic the very harsh, contrasty effect of direct noonday sunlight, a very tough challenge for most digital cameras. (You can read details of this test here.)

The Canon A640 had a little trouble with the deliberately harsh lighting in the test above, producing very high contrast with washed-out highlights and deep shadows. Noise suppression is visible in both shadows and highlights as well, contributing to the loss of detail, made more severe in these areas; though again, the camera's high resolution means that the detail present is still reasonable. The exposure compensation required, +1.0, did blow out much of the shirt to get the skin tones right, but the result is decent for a bad situation. (In "real life" though, be sure to use fill flash in situations like the one shown above; it's better to shoot in the shade when possible.)

Low light:
The Canon PowerShot A640 did very well in our low light tests, producing bright images at the lowest light levels at ISO 200 and above. At ISO 80 and 100, images were bright down to the 1/8 foot-candle level, about 1/8 as bright as average city street lighting at night. The one limitation though, is that you have to resort to Shutter Priority or Manual exposure mode to get exposure times longer than 1 second. As seen by the type in even the darkest images, the auto focus system worked well, relying on its AF assist lamp to find focus at the very darkest levels, but was also able to focus down at a bit less than 1/4 foot-candle without resorting to the AF assist. Given that typical city street-lighting at night is about one foot-candle (the brightest level shown in the test above), the Canon A640 should have no trouble handling the after-dark photography needs of most consumers.

NOTE: This low light test is conducted with a stationary subject, and the camera mounted on a sturdy tripod. Most digital cameras will fail miserably when faced with a moving subject in dim lighting. (For example, a child's ballet recital or a holiday pageant in a gymnasium.) For such applications, you may have better luck with a digital SLR camera, but even there, you'll likely need to set the focus manually. For information and reviews on digital SLRs, refer to our SLR review index page.

Coverage and Range
The A640's small flash has a limited range, produces a slight blue cast in combination with typical incandescent room lighting. Our standard shots required more exposure compensation than average.

Flash coverage was rather uneven at wide angle but very good at telephoto. In the Indoor test, the flash on the A640 underexposed our subject at its default setting, requiring a +1.0 EV exposure compensation adjustment to get reasonably bright results.

Even at 16 feet, our most distant test range, the flash did illuminate the DaveBox target adequately. This agrees with camera's own spec of 14 feet for flash range, on the long side for a compact camera model.

Our standard test method for flash range uses a fixed setting of ISO 100, to provide a fair basis of comparison between cameras. We now also capture two shots using the manufacturer-specified camera settings, at the range the company claims for the camera, to assess the validity of the specific claims. In the shots above, the A640 seems to perform exactly as Canon says it will, producing good exposures at the rated distances with its ISO set to Auto. While the range is rather limited, the good news here is that the camera doesn't seem to be significantly boosting its ISO. This would produce greater flash range, but at the cost of higher image noise, and the noise levels from the Canon A640 seem quite acceptable.

Print Quality
Great print quality, great color, very usable 16x20 inch prints. ISO 800 images are quite good at 8x10, acceptable at 11x14.

Testing hundreds of digital cameras, we've found that you can only tell just so much about a camera's image quality by viewing its images on-screen. Ultimately, there's no substitute for printing a lot of images and examining them closely. For this reason, we now routinely print sample images from the cameras we test on our Canon i9900 studio printer, and on the Canon iP5000 here in the office. (See the Canon i9900 review for details on that model.)

With the Canon PowerShot A640, we found that it had enough resolution to make very crisp 13x19 inch prints, but they were also quite good at 16x20! At ISO 800, its prints were still good at 11x14, and quite good at 8x10 and below. Color-wise, the PowerShot's images looked really great when printed on the iP5200, with bright, vibrant color that doesn't go overboard.