Sigma SD1 / SD1 Merrill In-depth Review
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.
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 (which when talking about line pairs is 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 - such as the Foveon X3 sensor in the SD1 - can deliver resolution equal to its Nyquist limit when coupled with a 'perfect' lens. Therefore, even though it may be near-unattainable 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 the latter we've used Sigma Photo Pro for conversion with sharpening set to a minimum, followed by unsharp mask in Photoshop:
- Load Raw file into Sigma Photo Pro
- Set Sharpness to -2 (all other settings default)
- Open file to Photoshop
- Apply a Unsharp mask tuned to the camera, here 150%, Radius 0.3, Threshold 0
- Save as a TIFF (for cropping) and as a JPEG quality 11 for download
|JPEG (4704 x 3136) 5.73MB||Raw (4704 x 3136) 3.67MB|
The crops above show that, freed from the blurring effect of an anti-aliasing filter, the SD1's Foveon X3 sensor resolves extremely highly in this test. It's capable of distinguishing the lines on our resolution chart right up to its Nyquist frequency, and continues to render line structure some way beyond. This 'false' detail is the flipside to the lack of an anti-aliasing filter, and while purists may object that it's not an accurate reflection of the scene, it does tend to help make real-world images look more detailed. Notably there's not even a hint of colour moiré, because the X3 sensor records full-colour information at every pixel location.
Compared to its APS-C competitors, the SD1 outresolves Bayer-sensor cameras with similar or slightly-higher output pixel counts such as the 16.3MP Pentax K-5 or 18MP Canon EOS 7D. But compared to the 24MP Sony Alpha SLT-A77, things are much closer, although as we'd expect the Bayer-sensor camera shows more colour artefacts.
Feb 21, 2013
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Apr 10, 2012
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