Ultimate Guide for Camera Sensors

It is obvious that the the quality of image your camera captures is not determined by Megapixels alone.  The real elements that determine the quality of a camera’s sensors are measured in the ISO Sensitivity of the Sensor, the Signal to Noise Ratio (Measured at 18%), the Dynamic Range, Tonal Range and the Color Sensitivity.

DxO Labs created dxomark.com for members of the digital photographic community who are passionate about image quality – professional photographers, advanced amateurs, photography reviewers and imaging media journalists. While other websites publish information about JPEG image quality, only DxO Labs provides the first publicly-accessible database of objective and in-depth RAW sensor image quality measurements.

From http://www.dxomark.com

ISO Sensitivity indicates how sensitive the camera sensor is with respect to light. In terms of exposure, the higher the ISO sensitivity, the better, as less light is needed to make an exposure. However, increasing the light sensitivity (from analog or digital gain amplification) also increases the image noise. On this graph we compare manufacturer-provided ISO number (indicated in the image’s Exif), versus the DxO Labs measured ISO (as defined in the ISO #12232 standard). ISO Sensitivity is also referred to as ISO Speed.

The signal-to-noise ratio (SNR) indicates how much noise is present in an image, compared to the actual information (signal). The higher the SNR, the better, as less noise will be present in the image. The scale is logarithmic (in dB): + 6dB means two times less noise (as a reminder 3dB corresponds to 1 f-stop or 1EV).The SNR is here measured at the image mid-dynamic (which corresponds to a gray with 18% reflectance, commonly accepted as the average photographic scene reflectance).

Dynamic range or light sensitivity range of a sensor indicates the ratio of light exposure between the highest brightness a camera can capture (saturation) and the lowest brightness it can effectively capture (typically when noise becomes more important than signal, i.e., SNR < 0 dB). This range indicates the maximum contrast that can be effectively captured by the sensor. The larger the dynamic range, the better, as the sensor is able to capture higher-contrast scenes. Note that dynamic range is expressed on a logarithmic scale in EV (same as f-stop), thus an increase of 1EV corresponds to a doubling of dynamic range.

Tonal range indicates how many gray levels are distinguishable up to noise in an image. The tonal range corresponds to an integration of the signal-to-noise ratio (SNR) over the dynamic range of the sensor, and is therefore representative of the average noise level. The larger the tonal range, the better the image: noise is lower, and subtle nuances can be distinguished. It is expressed on a logarithmic scale as the bit depth necessary to encode that number of gray levels: an increase of 1 bit of tonal range corresponds to doubling the number of distinguishable gray levels.

Color sensitivity is an extension of tonal range that takes into account the color rendering involved in raw conversion: it basically indicates how many colors are distinguishable in an image, up to noise. Typically, if the sensor is slightly color blind, color rendering implies a strong digital color amplification and therefore a strong increase of noise. The greater the color sensitivity, the better the image: noise will be lower and with lower coloration. Color sensitivity is expressed on a logarithmic scale as the bit depth needed to encode a given number of colors: an increase of 1 bit of color sensitivity corresponds to doubling the number of distinguishable colors.

Site Screen Grab (Comparing some Nikons that I use and showcases the powerful comparision tools. View the Comparison of a Nikon D200 (DX Sensor), D300 (DX Sensor) & D700 (FX Sensor) here.

Updated Information (1.29.2009)

ISO Lies.  When ISO 100 is really 72..