Noise, resolution and sensitivity
Image: The gradation on the fleece is a little smoother and less ‘blocky’ in the processed raw file than in the JPEG image. There is also more detail in the raw image
As the images of our resolution chart show, the EOS 550D is capable of resolving a lot of detail at the lower sensitivity settings, and it is on a par with the EOS 7D. The most detail-rich images are captured in low-sensitivity raw files when the level of noise reduction applied using the supplied processing software, Digital Photo Professional (DPP), is kept to a minimum.
Images captured at the highest sensitivity setting, equivalent to ISO 12,800, contain a fair amount of chroma and luminance noise. When the high-sensitivity noise reduction is turned off, the level of noise in JPEG images is approximately double the amount that is present in JPEG files captured with the noise reduction set to its standard setting. Although applying noise reduction doesn’t obliterate all detail, there is an inevitable loss and more detail can be drawn from simultaneously recorded raw files. However, when the luminance noise reduction in DPP is set to zero, the ISO 12,800 raw files develop a crosshatch pattern (as do the EOS 7D’s) that is visible at 100% on the computer screen. This can impart a gritty texture to images sized for making large prints and it may therefore be preferable to apply a little luminance noise reduction.
Left: These images show 72ppi (100% on a computer screen) sections of images of a resolution chart, captured using matching 105mm macro lenses. We show the section of the resolution chart where the camera starts to fail to reproduce the lines separately. The higher the number visible in these images, the better the camera’s detail resolution is at the specified sensitivity setting. Right: This graph shows the brightness values recorded by the test camera when it is used to photograph a stepped graduation wedge. The wedge has transmission values in 1⁄2EV steps ranging from 0 to 12EV. The camera’s exposure is set so the 12EV section in the wedge has a brightness value of 255. Software analysis of the image then determines the recorded brightness values of all the other steps and calculates the camera’s dynamic range.
