Resolution Chart Comparison (JPEG and RAW)
Images on this page are of our standard resolution chart which provides for measurement of resolution up to 4000 LPH (Lines Per Picture Height). A value of 20 equates to 2000 lines per picture height. For each camera we use the relevant prime lens (the same one we use for all the other tests in a particular review). The chart is shot at a full range of apertures and the sharpest image selected. Studio light, cameras set to aperture priority (optimum aperture selected), image parameters default. Exposure compensation set to deliver approximately 80% luminance in the white areas.
NEW: This is a slightly new treatment of resolution, intended to streamline the amount of information that we include in our tests. As always though, we've made the original images available for download (just click on the magnifying glass on the thumbnail below) so you can still take a look at the camera's raw and JPEG output yourself, using your choice of raw conversion/sharpening workflow.
What we want to show here is how well the camera is able to resolve the detail in our standard test chart compared to the theoretical maximum resolution of the sensor, which for the charts we shoot is easy to work out - it's simply the number of vertical pixels (the chart shows the number of single lines per picture height, the theoretical limit is 1 line per pixel). Beyond this limit (when talking about line pairs usually referred to as the Nyquist frequency) the sensor cannot faithfully record image detail and aliasing occurs.
This limit is rarely attained, because the majority of sensors are fitted with anti-aliasing filters. Anti-aliasing filters are designed to reduce unpleasant moiré effects, but in doing so, they also reduce resolution (the relative strength and quality of these filters varies from camera to camera). In theory though, a sensor without an AA filter, when coupled with a 'perfect' lens, will deliver resolution equal to its Nyquist limit. Therefore, even though it may be effectively unattainable with normal equipment in normal shooting situations, an understanding of a sensor's theoretical limit provides a useful benchmark for best possible performance. Nyquist is indicated in these crops with a red line.
On this page we're looking at both JPEG and Raw resolution. For a (more) level playing field we convert the latter using Adobe Camera Raw. Because Adobe Camera Raw applies different levels of sharpening to different cameras (this confirmed) we use the following workflow for these conversions:
- Load RAW file into Adobe Camera RAW (Auto mode disabled)
- Set Sharpness to 0 (all other settings default)
- Open file to Photoshop
- Apply a Unsharp mask tuned to the camera, usually 100%, Radius 0.7, Threshold 0
- Save as a TIFF (for cropping) and as a JPEG quality 11 for download
|Canon EOS 550D (JPEG, 4.6MB, 18.0 MP)||Canon EOS 550D (RAW, 5.2MB, 18.0 MP)|
|RAW (ACR 5.7)|
|JPEG||RAW (ACR 5.7)|
Unsurprisingly, the anti-aliasing filter on the EOS 550D's sensor has a measurable impact on the sensor's ability to record detail. In both raw and JPEG output, the 550D ceases to be able to deliver accurate resolution information well before the Nyquist cutoff. It isn't uncommon for raw files to contain some semblance of structure up to and slightly beyond Nyquist, as you can see from the horizontal resolution images above, but this isn't 'true' detail (the sensor simply doesn't have enough pixels), and represents only how good the camera/raw converter is at guessing what lies beyond Nyquist.
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