Color (8.12)
As with all digital cameras that we review, we tested the Casio S770 by photographing an industry standard color chart manufactured by GretagMacbeth. We set the ISO to 50 to keep noise as minimal as possible and manually set the white balance to keep colors as accurate as possible under our studio lighting.
Once the pictures of the chart were taken, we uploaded them to Imatest imaging software. This program analyzed the ability of the Casio S770 to depict colors as compared to the industry standard chart. Below is a chart output by Imatest to show the differences between the ideal colors from the GretagMacbeth chart (the inner vertical rectangle of each tile) and the colors from the Casio Exilim EX-S770 (the outer square of each tile). The inner portion of the square represents the ideal corrected for luminance by Imatest.
Most of the colors look good, but the difference is better seen on the following chart. It shows the camera’s colors as circles on the color spectrum and the ideal colors as squares. The line sometimes seen connecting the two represents the degree of error; obviously, this shouldn’t be seen at all.
Circles that bend to the outer edges of the chart are over-saturated and those that lean toward the center are under-saturated. The Casio S770 does a nice job in terms of saturation with 99.66 percent saturation – very nearly perfect. The camera performed fairly well in terms of pure color accuracy too with a mean color error of 7.4. This resulted in an overall score of 8.12, which bests the older Casio S600’s score of 6.7 by a long shot.
Still Life Scene
Below is a shot of our beloved still life composite captured with the Casio Exilim EX-S770.
Click on the image above to view the full resolution file.
Resolution (3.69)
The Casio Exilim EX-S770 has 7.2 effective megapixels on its image sensor, a slight upgrade from the S600’s 6-megapixel count. To see how detailed the S770’s pictures really are, we photographed an industry standard resolution chart under optimal lighting at various exposure settings. With the ISO set to its lowest at 50 and the white balance manually adjusted, we snapped the photos and uploaded them to Imatest software. The program looked through all the images and selected the sharpest shot, which happened to be taken with a focal length of 19mm and an aperture of f/5.2.
Click on the chart above to view the full resolution version
Imatest also determined how sharp this image is in units of line widths per picture height (lw/ph), which describes how many black and white alternating lines could theoretically fit across the frame without the S770 blurring them together. The Casio Exilim EX-S770 resolved 1663 lw/ph horizontally with 9.3 percent oversharpening, and 1388 lw/ph vertically with 7.78 percent undersharpening. The older Casio S600 had more consistent sharpening results but captured less detail with its 6-megapixel image sensor. The Casio S770 may have read more line widths per picture height, but it didn’t do proportionately better for having another megapixel on its sensor. Thus, the S770 comes out with a lackluster 3.69 resolution score.
Noise – Auto ISO (1.74)
In the bright studio lights, the Casio Exilim EX-S770 automatically picked out an ISO 200 setting and produced more noise than most cameras do. This is quite disappointing for a camera that point-and-shooters will rely on to automate the ISO frequently.
Noise – Manual ISO (4.2)
In the studio, we manually set the ISO to its 4 settings: 50, 100, 200, and 400. Below is a chart that shows the correlation between noise (vertical axis) and the ISO setting (horizontal axis).
While all digital cameras show an increase in noise as the ISO is bumped up, the Casio Exilim EX-S770 increases more than is usual within its already short manual ISO range. Most point-and-shoot cameras offer manual ISO settings to 800 and 1600, and some even to 3200 at full resolution. The S770, however, doesn’t offer much and what it does have shows more noise than it should.
Low Light (4.0)
We turned down the studio lights to 60, 30, 15, and 5 lux to see how the camera would react in less than ideal conditions. It seemed to do okay at 60 lux, which is about the light garnered from two soft lamps in an otherwise dark room. When the light waned further, though, the S770 had a lot of problems.
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Low Light Tests
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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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First of all, the Casio S770 had a hard time balancing on a tripod, so long exposures were tough even when the picture was taken with the self-timer. The auto focus system was unreliable and had difficulty focusing in anything less than 60 lux. And the limited ISO range hurt the camera’s ability to capture images at all.
When the shutter is open for longer periods of time, noise usually increases in the image. We tested the camera at a few shutter speeds from 0.5-4 seconds and plotted them on the chart below. The shutter speed is located across the horizontal axis and the percentage of the image turned into noise shows on the vertical axis.
This is the opposite of what we usually see: most cameras show a curve starting with lower noise at the faster shutter speeds and progressing into more noise as the shutter is left open longer. As evidenced by the graph, the Casio S770 has a very aggressive noise reduction system that looks good on paper (in text, not prints). Once the images are examined, though, viewers can see the details disappear and edges become increasingly smoother and smoother.
Between the noisy half-second pictures, the smooth and detail-less 4-second shots, the lack of decent auto focus, the inability to stabilize on a tripod, and the disappointing max ISO setting of 400, the Casio Exilim EX-S770 shouldn’t be used in dim lighting. Ever.
Dynamic Range (5.25)
We wanted to see how well the Casio S770 could capture a variety of light and dark shades, so we photographed a step wedge that shows rows of rectangles from black to white.
The images were analyzed with Imatest, which determined how many of those exposure values were depicted. The high-quality dynamic range is shown as the blue line and has up to 1/10 of a stop of noise. The low-quality range has up to a full stop of noise and is represented by the red line. Both measurements are useful: the high quality more for subjects and the low quality for throwing texture into backgrounds.
The Casio S770 showed average performance for an ultra-slim point-and-shoot digital camera. It had a little surprise with a bit less dynamic range at ISO 50 than at ISO 100, but then the camera went downhill around ISO 200. This is expected in most cameras, but farther into the ISO range. There isn’t much farther to go with the S770’s short sensitivity range, but this is still disappointing because many pictures will be taken using the ISO 200 and 400 settings.
Speed/Timing
Startup to First Shot (8.6)
The Casio S770 started at a leisurely pace. It took 1.4 seconds to wake up and snap its first shot.
Shot-to-Shot (9.5)
The Casio Exilim S770 has High and Normal burst modes. The High mode snaps a shot every half-second, but for only 3 pictures at a time. After the 3 pictures, the camera takes 2.5 seconds to write them to the memory card before shooting another round. The Normal burst mode shot images continuously without a hiccup, but wasn’t as fast with a shot taken every 1.4 seconds.
Shutter-to-Shot (8.9)
It was hard to get any measurement at all, which is great news. Most point-and-shoot cameras have some shutter lag, but the S770 performed well with its quick auto focus system.
