We shoot a specially designed chart in carefully controlled conditions and the resulting images are analysed using DXO Analyzer software to generate the data to produce the graphs below.
For more more details on how to interpret our test data, check out our full explanation of our noise and dynamic range tests.
Signal to noise ratio
A high signal to noise ratio (SNR) indicates a cleaner and better quality image.
JPEG images from the Nikon D3100 compare reasonably well with the Pentax K-r and Sony Alpha 390 up to a sensitivity value of ISO 800. However at higher sensitivity values the Nikon D3100 lags behind. Up to around ISO 1600 the Canon EOS 1100D leads the way.
Raw signal to noise ratio
Raw images (after conversion to TIFF) from the Nikon D3100 show lower signal to noise ratio scores than the Pentax K-r, Sony Alpha 390 and Canon EOS 1100D. This means that the Nikon D3100's images are likely to contain more noise and have a little less detail.
This chart shows that the Nikon D3100's JPEGs capture a wide tonal range up to a sensitivity of ISO 1600, at higher ISO settings detail is easily lost in the shadows and highlights.
Raw dynamic range
This chart indicates that the Nikon D3100's raw images (after conversion to TIFF) capture a wide tonal range up to a sensitivity of ISO 3200, beating the Sony Alpha 390 and coming close to the performance of the Canon EOS 1100D. However, it can't match the Pentax K-r for dynamic range across its entire sensitivity range.