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JPEG Quality / Image Sizes


Standard Test Scene

The PowerShot A20 supports nine combinations of JPEG compression levels (quality) and image size. You can select from one of three image sizes (L/M/S); 1600 x 1200, 1024 x 768 or 640 x 480 and three different JPEG compression levels; Super-Fine (5 bpp), Fine (3 bpp) and Normal (2 bpp). The A20 does not have an uncompressed TIFF or RAW mode.

To give an impression of what some of the combinations of image size and quality produce the table below is a cross reference of some of them:

  • 1600 x 1200 Super-Fine
  • 1600 x 1200 Fine
  • 1600 x 1200 Normal
  • 1024 x 768 Super-Fine
  • 1024 x 768 Fine
  • 1024 x 768 Normal
  • 640 x 480 Super-Fine

Images below are cropped 240 x 100 area of the image magnified 200% (nearest neighbour).


 
1600 x 1200
Super
Fine

953 KB
Fine
589 KB
Normal
275 KB
 

 
1024 x 768
Super
Fine

424 KB
Fine
267 KB
Super
Fine

133 KB
 

 
640 x 480
Super
Fine

184 KB

There's a noticeable increase in JPEG artifacts as we move up the compression ratios (file sizes decrease), for most SuperFine 1600 x 1200 will be the main choice, best resolution and virtually no artifacts.


Picture Effects

The A20 only has one picture effect and that's a black and white mode. You access it by setting the white balance to black and white, here's a sample of the difference between normal colour mode and the black and white mode.

Normal colour Black & White


Digital Zoom

Readers of my reviews will know I'm not a huge fan of digital zoom as it's often a badly implemented and seldom used (by owners) marketing "ploy" to sell cameras which don't have an optical zoom. The PowerShot A20 features a 3 x optical zoom and beyond that a digital zoom up to 2.5x.

Digital Zoom is implemented by cropping (selecting the mid part of the image) and sampling-up, the only advantage in doing digital zoom inside the camera is (a) if you don't have any photo software to magnify (and interpolate) the image or (b) to digitally zoom without zooming the JPEG artifacts.

Zoom: 3 x (105 mm optical, no digital)
Zoom: 6 x (105 mm optical, 2 x digital)
Zoom: 7.5 x (105 mm optical, 2.5 x digital)


Macro focus mode

The A20's macro focus mode allows you to get (according to the manual) 16 cm (6.3 in) away from the subject, under our testing we found that this combined with about three quarter zoom would produce sharp macro shots. The best frame coverage we managed was 8.3 cm (3.27 in) across the frame.


Internal Flash

The A20's flash unit is larger and more powerful than that found in the IXUS 300, with a quoted range of Wide: 0.76 m - 4.2 m (2.5 - 13.8 ft), Tele: 0.76 m - 2.5 m (2.5 - 8.2 ft). It does, however, seem to perform in about the same manner, perhaps a little warmer with a little more power.

Skin tone test, accurate, skin tones, if a little on the warm side (though this is preferable to the cold blue cast you can get from some flash units). This is our wide-angle wall shot test, we're just 2 m (6.6 ft) away from the wall here and the flash is definetly exhibiting drop off at the edges of the frame. Colour chart flash exposure. Good exposure, accurate colours without any noticeable cast.

Footnote: the A20's AF assist lamp proved to be far less effective than that found on the IXUS 300, it's of a different type and is mounted behind the flash window. The hand shot above was especially difficult as the camera refused to focus correctly, it had to be focused first on a nearby painting and then moved over (with the shutter release half-pressed) before taking the shot.


Stitch Assist mode

The PowerShot A20 features two Photo Stitch modes, one from left to right and another from right to left. I would really have liked to have also seen a vertical and/or square stitch modes too.

When using the PhotoStitch mode the camera displays the last quarter of the previous image to help alignment of the next frame, to ensure proper matching of the stitched images the camera locks exposure and white balance to the first exposure.

The PowerShot A20 comes with Canon's own Photo Stitch software (both Windows & Mac), although it's relatively good it's no match for my personal favourite stitching software, PanaView Image Assembler. The panorama below was produced using PanaView Image Assembler from three images taken by the A20 in Stitch Assist mode (you can grab the originals here: one, two, three).

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Comments

Pascal Parvex

Just bought one off Ebay for like 15 bucks. I once had the A10 and now want to lay my hands on the big brother I always wanted.

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