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DxOMark has introduced a new metric of lens sharpness that it's calling the 'Perceptual MegaPixel'. This is designed to give a simple, easily-understandable indication of how a lens impacts on the resolution of the camera with which it's paired. The measurement is based on standard MTF (Modulation Transfer Function) testing, but also takes into account the sensitivity of the human visual system to detail. The data can be explored over at the DxOMark website, www.dxomark.com.
Our lens reviews are prepared in partnership with DxOMark, using test data shot in its labs. Do you think the 'Perceptual Megapixel' would be a useful number to include in our reviews? Let us know in the comments below.
A simple way to quantify the impact of lens sharpness on camera resolution
December 17, 2012 - DxOMark, the website of reference for measuring the image quality of digital cameras and lenses, announces the launch of the Perceptual Megapixel, its new measure of lens sharpness. Expressed in units already well-known to the general public, the Perceptual Megapixel provides photographers with a means of instantly understanding the performance of a lens by quantifying its impact on the perceived resolution of the camera with which it is coupled.
Designed by DxOMark experts, Perceptual Megapixel quantifies the sharpness "perceived" by the photographer while taking into account all the characteristics and defects of the lens and the camera.
"This new unit of measure replaces the MTF scores that we have been publishing up until now. Perceptual Mpix weights MTF measurements with the sensitivity to detail of the human visual system, thus providing a score for the sharpness perceived by our eyes. We think this new measurement will be more understandable and practical for photographers who use our website," explained Frédéric Guichard, Chief Scientific Officer for DxO Labs.
The Perceptual Megapixel measurement allows for making numerous comparisons among cameras and for the first time quantifies the impact of lens sharpness on camera resolution. Thus the perceived resolution for a camera can be significantly different from the native resolution depending on the lenses with which it is coupled.
For example, when coupled with a Canon EOS 5D Mark II camera with a 21.1 Mpix sensor, a Sigma 35mm F1.4 DG HSM lens has a Perceptual Mpix score of 17.2, whereas a lens such as the Carl Zeiss Distagon T* 35mm f/1.4 ZE has a Perceptual Mpix score of 15.2.
The example above is based on data from DxOMark's database of test reults for more than 2,700 camera and lens combinations. These tests reveal that, on average, about 45% of the resolution is lost due to lens defects.
"The Perceptual Megapixel measurement allows photographers to step away from manufacturers' announcements about resolution and to answer a key question when the time comes to change equipment: would it be better to buy a new camera or a new lens?" observed Nicolas Touchard, VP Marketing, Image Quality Evaluation, for DxO Labs.
This new metric introduced by DxOMark aligns with the standardization work currently being undertaken by the IEEE, the International Imaging Industry Association (I3A), and the ISO - and in which DxO Labs actively participates. Perceptual Mpix is also based on the scientific findings of CNES (the French space agency) pertaining to the optimization of digital acquisition, notably in the field of satellite imagery.
Freely available to all, DxOMark has been designed to serve the entire photographic community, from serious amateur photographers to photo experts and journalism specialists. It has a threefold mission: to provide objective measurements of digital cameras and lenses; to analyze camera and lens performance; and to provide a means for making meaningful comparisons.
DxOMark now has a database of more than 2,700 available camera/lens combinations. Dozens of DxO Labs engineers and technicians in six DxO laboratories perform these measurements, taking a photo every 10 seconds. Testing protocols are entirely reproducible and conform to the international standards established by the Camera & Imaging Products Association (CIPA), the International Imaging Industry Association (I3A), and the Camera Phone Image Quality (CPIQ) group.