Replacing the Ixus 860 IS, Canon's new Ixus 870 IS features the new DiG!C 4 image processor and a slightly larger imaging chip with 10-megapixel (effective) resolution. The weight of the two camera bodies is the same but the new model is slightly longer, not quite as high and almost 2 mm slimmer. Available with a silver or gold metal front panel, the new model has a slightly longer zoom range but retains its useful 28mm (equivalent) wide-angle coverage. The image processor has also been upgraded.

Cosmetically the changes reflected in the new model - aside from the new colour option -  are relatively minor. On the front panel, the electronic flash tube is slimmer and the matte black ring surrounding the lens module is replaced by a shiny metallic ring. The top panel controls have undergone minor re-styling but their functionality remains the same.

 
Front view of the Ixus 870 IS, showing the silver colour option.

 
Rear view showing the large LCD panel and main button controls.

 
Top view showing the shooting mode selector slider, shutter button and zoom lever.

On the rear panel, the Print/Share and Playback buttons have been swapped around and the knurled Control Dial around the arrow pad is slightly wider. When a double-ended arrow appears in the top right corner of the LCD (see illustration below), you can shift between the Auto and the new Program shooting mode by rotating this Control Dial.

 
The Control Dial provides a quick way to swap between Auto and Program (P) shooting modes.

Replacing the Camera Manual setting on earlier Ixus models, the Program mode provides similar functionality, allowing you to adjust a wider range of camera settings than the alternative Auto and Special Scene modes. Program AE is accessed by turning the Control Dial that surrounds the Function/Set button. You must first select the Camera mode from the slider on the top panel (which has positions for the Movie, Scene and Camera shooting modes).

 
In Program AE mode, you have full access to key settings via the Func./Set button.

The actual operation of the arrow pad hasn't changed. The Menu and Display buttons are slightly larger and more closely integrated into the camera body. The LCD panel, which is the same as the Ixus 860 IS covers most of the rear of the camera. No viewfinder is provided and the rechargeable NB-5L battery is the same. Both cameras come with 32MB SD cards. No internal memory is provided.

Most functions introduced with the earlier model are carried over, albeit with a few improvements due to the new image processor. Thus the image stabiliser, flash modes, in-camera red-eye correction, auto ISO shift, focus check and battery level indicators are essentially the same. Other unchanged features include the ISO sensitivity range, white balance, shutter speed and exposure compensation settings, image parameter settings, self-timer and digital zoom magnification.

Canon's new DIGIC 4 processor improves operating speeds and applies better noise-reduction processing (which will be necessary, given the Ixus 870 IS's higher resolution). It also drives several intelligent technologies to make it easier for novice users to take in-focus, correctly exposed pictures. The Face Detection system can now detect faces positioned at an angle to the camera, or in profile. The Face Select & Track function can track a specific subject even more accurately, while a new Face Self-timer function makes group shots and self-portraits easy.

This setting allows you to compose a group shot and press the shutter button before joining the group. The camera will move into standby mode while Fact Detection engages.  Two seconds after a face is detected, it will capture three shots, from which the 'keeper' can be selected. If no face is detected the shutter will release after 30 seconds (but only one shot is taken).

Improvements to Motion Detection Technology enable the camera to register camera and subject movement, then automatically adjust ISO to prevent image blur - provided the ISO is set to Auto. A new Servo AF function continuously re-focuses on subjects moving towards or away from the camera. DIGIC 4 also powers Canon's new i-Contrast feature, which brings out natural-looking detail in dark areas of pictures without blowing out highlight areas.
The exposure metering system also takes advantage of Fact Detection processing. As in the Ixus 860 IS, the Evaluative mode is automatically linked to the Face Detection frame. In the new model, Spot metering can also be linked with Face Detection.

 
The Scene menu selections are initially displayed on a 'rotating' half-wheel.

The addition of a new Sunset mode to the Special Scene settings brings the total number of shooting modes to 19, an increase of two on the 860 IS. The Scene mode also contains an interesting Digital Macro function that lets you shoot much closer than the standard close-up mode (which focuses to 2 cm). It appears to work by cropping the image, although depth-of-field is very shallow so some digital processing may be involved.

The Time-lapse video recording function is not available on the IXUS 870 IS and HD video recording is not supported.  However, although video resolution and clip length limits are unchanged from the Ixus 860 IS, the movie format on the new camera has been changed to H.264 for video plus Linear PCM (LPCM) for audio to free up extra memory.

 
Movie recording times are displayed on the lower right corner of the LCD screen.

The new H.264 format, which is also known as MPEG-4 Part 10 or MPEG-4 AVC, provides more efficient data compression and greater flexibility for networked environments. It is used in a number of standards, including Blu-ray and broadcast television as well as HDMI. LPCM is generally used in conjunction with the WAV container format for uncompressed audio on PCs and also for lossless encoding of audio data in the CD, DVD and Blu-ray standards. (Voice memos are still recorded in WAV format.) 

Image Capture
Image files can only be stored as JPEGs and the camera supports five resolution settings with a 4:3 aspect ratio plus a Widescreen setting that records images at 3648 x 2048 pixel resolution. Three compression levels are provided: Superfine, Fine and Normal. Typical file sizes are shown in the table below. 

Two resolution settings are provided for movie clip recording: VGA and QVGA. Only one frame rate (30 frames/second) is supported but you can use the colour accent and colour swap settings with both resolutions. Typical recording times for a 1GB memory card are shown in the table below.

Maximum length of video clips is one hour and recording will stop when the file size reaches 4GB. Use of SDHC cards with speed class of 4 or higher is recommended. 

Playback
Pressing the Playback button on the rear panel displays the last image taken. You can scan through other images on the memory card by turning the Control Dial. Moving it clockwise displays images in the order they were taken; going anti-clockwise shows the reverse order. Images can be deleted one-by-one in playback mode or tagged for automatic printing.

 
Basic shooting data can be overlaid on images in playback mode.

 
You can also view images by their shooting date.

Playback zoom of up to 10x is supported for checking focus. The Focus Check function lets you magnify faces in group shots taken with Face Detection to ensure their eyes are open and their expressions are as desired. Slideshow playback is also supported and you can select images to be played in this mode and also choose any of three transition effects.

 
Slideshow transitions are selected on the first page of the playback menu.

You can view images in sets of nine thumbnails and use the zoom lever to search though shots nine at a time. Alternatively, by pressing the upper section of the arrow pad you can move into Jump mode, which lets you choose from six Jump options by pressing the horizontal parts of the arrow pad. Options include jumping by 10 or 100 images, jumping by date, to a Category or Folder or to a Movie.

 
Jump options in playback mode.

 
The playback menu also lets users allocate images to different Categories to make searching easier and faster.

Searching filters allow you to locate images that have been edited, protected or DPOF-tagged. Menu items are provided for erasing selected images or all images, organising images in categories, rotating, resizing and trimming images and adding effects via the My Colours function.

 
My Colours adjustments can be applied to images in Playback mode. The results are saved as separate files.

You can also use the i-Contrast setting to apply brightness compensation to backlit shots or images that are too contrasty and save the result as a new file.

 
 iContrast adjustments are applied by selecting iContrast in the playback menu.

 
Four adjustments are provided: Auto, Low, Medium and High.

In-camera red-eye correction is provided and sound bites up to a minute log can be attached to still images. The camera comes with an AV cable for displaying images and video clips on a TV set. However, HDTV playback is not supported.

Performance
The test camera produced images that were sharp and bright with natural-looking colours and slightly elevated contrast and saturation. Autofocusing was fast and mostly accurate, although we sometimes had to set the AF frame to centre and the frame size to small then use AF lock in order to force the camera to focus on a specific area in the frame. AF point selection is not provided in this camera.

Photo Review's tests showed the image stabilisation system capable of providing approximately two f-stops of shutter speed advantage, which was useful in overcast conditions. However it often failed to cope with moving subjects in low light levels. The dynamic range recorded in outdoor test shots was slightly better than average for a digicam and we were able to see detail in shadows in outdoor shots at normal exposure settings, although the brightest highlights were blown-out.

Imatest confirmed our subjective assessments of contrast, colour accuracy and saturation but revealed a few hue drifts, notably in lighter skin tones, yellow and cyan. Elevated saturation was found in reds and purplish blues. Resolution was marginally below expectations for a 10-megapixel digicam, although little difference was found between centre and edge resolution for most focal length settings.

Resolution remained relatively high between ISO 80 and ISO 400 but declined sharply thereafter. The graph below shows the results of Photo Review's Imatest tests.

Lateral chromatic aberration was low and we only detected slight coloured fringing in shots taken in contrasty outdoor lighting when they were enlarged to 100%. Flare and ghosting were negligible with backlit subjects. The auto white balance setting had the usual problems with incandescent lighting but produced neutral colours with fluorescent lights. Both the tungsten and fluorescent pre-sets also delivered neutral colours, as did the manual measurement system.

 
Coloured fringing coudl only be seen when shots were enlarged to 100%.

The flash required at least ISO 200 to illuminate an average-sized room. Flash exposures were well-balanced but image noise became apparent at ISO 800 and was obvious at ISO 1600. Close-ups were competently handled in both the normal macro and digital macro modes.

Low-light performance was above average for a digicam, with little apparent noise in 15-second exposures at ISO settings up to 400. Both pattern and colour noise were visible at higher ISO settings, where the loss of resolution also became visible. Movie performance was generally good, given the camera's limitations.

The test camera powered-up ready for shooting within one second and we measured an average capture lag of 0.5 seconds, which reduced to 0.1 seconds with pre-focusing. It took an average of 3.3 seconds to process a high-resolution image. In the continuous shooting mode, the camera recorded 10 shots in 5.9 seconds. Image processing appeared to be on-the-fly as it took only 3.8 seconds to process this burst of shots. 

IMATEST GRAPHS

SAMPLE IMAGES

Auto white balance with incandescent lighting.

 
Auto white balance with fluorescent lighting.

 
Close-up.

 
Digital macro.

 
Digital zoom.

 
Backlighting.

 
Indoor auto flash: 20mm focal length, 1/60 second at f/8, ISO 200 (Auto).

 
15-second exposure at ISO 200.

 
2-second exposure at ISO 1600.

 
5.0mm focal length, 1/640 second at f/5.6, ISO 200.

 
20mm focal length, 1/320 second at f/5.8, ISO 200.

Image sensor: 6.16 x 4.62 mm CCD sensor with 10.3 million photosites (10.0 megapixels effective)
Lens:  5.0-20.0mm f/2.8-5.8 (28-112mm in 35mm format)
Zoom ratio: 4x optical, up to 4x digital
Image formats: Stills – JPEG (Exif 2.2); Movies – MOV (Image data: H.264; Audio data: Linear PCM) (Mono)
Image Sizes: Stills – 3648 x 2736, 2816 x 2112, 2272 x 1704, 1600 x 1200 (Date Stamp), 640 x 480, 3456 x 2048 (Widescreen); Movies – VGA, QVGA at 30 fps
Shutter speed range:  15–1/1600 sec.
Image Stabilisation: Lens-shift type
Exposure Compensation: ±2 stops in 1/3-stop increments
Focus system/range: TTL autofocus with Face Detect/AiAF (9 points); range 50 cm to infinity; macro 2-50 cm
Exposure metering/control: Evaluative, Center-weighted average or Spot metering; Program AE plus 12 Scene pre-sets (Portrait, Night Snapshot, Kids & Pets, Indoor, Sunset, Foliage, Snow, Beach, Fireworks, Aquarium, Underwater, ISO3200)
ISO range: Auto , High ISO Auto , ISO 80, 100, 200, 400, 800, 1600
White balance:  Auto , Day Light, Cloudy, Tungsten, Fluorescent, Fluorescent H or Custom
Flash modes/range (ISO auto): Auto, on, off; Red-eye reduction/Red-eye correction/Slow Synchro settings available; range 0.3 to 4.2 m
Sequence shooting:  Approx. 1.4 images/sec.
Storage Media: SD/SDHC/MMC
Viewfinder: n.a.
LCD monitor: 3.0-inch TFT colour LCD (wide viewing angle type), approx. 230,000 dots (Picture coverage 100%)
Power supply:  NB-5L rechargeable lithium-ion battery
Dimensions (wxhxd): 93.8 x 56.8 x 23.6 mm
Weight: Approx. 155 grams (without battery and card)