Sigma DP1 Review
The Sigma DP1 is without doubt one of the most eagerly anticipated cameras of late, certainly in the compact camera sector. Sigma first presented a concept prototype of the DP1 at Photokina 2006 but the first production models only hit the shelves in March this year. Interest in the camera was so big that Sigma even took the very unusual step of explaining the delay in an official statement (unforeseen image quality problems which resulted in a requirement to change the specification of the camera's imaging pipeline).
So what is all the fuss about? It's the sensor. The DP1 uses the same Foveon X3 sensor as Sigma's SD14 DSLR and that makes it the first compact camera ever to be made with an SLR-sized sensor (it's around the same size as the Four-Thirds format). But not only the sensor differentiates the new Sigma from the zillions of compact cameras that are currently available. With its no-nonsense feature set and 28mm (35mm equiv.) prime lens the DP1 is a million miles away from the superzooms, smile modes and face detection functions that are nowadays standard on so many compact digital cameras.
On its dedicated DP1 website Sigma says it 'set out to create a camera that could translate an irreplaceable instant into a work of art of the highest order'. So has Sigma succeeded in living up to its own hype? Let's find out on the following pages, starting as ever with the headline specification:
- 14.06 million (4.69 million x 3) Foveon X3 CMOS sensor
- 28mm equiv, F4 lens
- RAW capture
- Full manual control
- TRUE image processing
- 230,000 pixel, 2.5-inch LCD
- Movies in 320 x 240 pixels (QVGA) @ 30 fps
Sensor size compared
As the graphic above shows, the DP1 has a considerably larger sensor area than most compact cameras, where 1/1.8" is almost as large as you'll get these days. Although not as large as the APS-C sensors found in most consumer level DSLRs, the Sigma's X3 sensor is a lot nearer than any other compact.
Foveon X3 sensor background
- Photodetector - A physical device used to capture a single color value (for a Bayer camera there is one of these per pixel location, the X3 sensor has three per pixel location)
- Pixel location - A location on the final image which contains full RGB color information
What's so good about the Foveon X3 sensor?
In the example below we are simplifying things by using a 130 x 130 sensor, thus a total of 16,900 pixel locations in the output image. Obviously the same rules apply no matter many pixel locations the final image has.
Traditional "Mosaic" sensors
Digital cameras have for years used what is essentially a monochromatic (b&w) image sensor with individual color filters over each photodetector (known as the Bayer pattern and normally in a GRGB pattern). This means that each photodetector can only detect one of either red, green or blue light. Note that the green channel has twice the number of photodetectors as red or blue (this is because the majority of luminance information is carried in the green channel). A demosaic algorithm then combines the color of neighboring pixels to reproduce the scene color at that pixel location.
Foveon's X3 sensor
Foveon's sensor instead of having a single photodetector at each pixel location has a multi-layered design which has the equivalent of a red, green and blue photodetector at each pixel location. This means that instead of having to interpolate the values of neighboring pixels the X3 sensor 'sees' full color at individual pixel locations. This is pretty much the 'holy grail' of digital image sensors, it should mean ultra sharp, detailed images with full color single pixel resolution.
Note that this is a simplified drawing of how the chip works, for more detail see our news article at the time.
16,900 pixel locations