The “perceptual megapixel” is a new unit of image quality measure, the perceptible quality of a camera with a certain lens on it. It has been developed by DxOMark, the image quality benchmark site. The site till now measured the lens-camera performance in terms of line pair count per mm, transmission (T-stop), vignetting or chromatic aberrations. For sensors, DxOMark measures color depth, dynamic range or sensibility and low-light quality with signal/noise ratio. With the “perceptual megapixel” DxOMark developped a new indicator of sharpness, more meaningful than the number of line pairs per mm and more appropriate than the standard set up there is a good ten years through its measurement software DxO Analyzer, the BXU. The advantage of “perceptual megapixel” is to be measured in “megapixels”, a unit that talks to all photographers ans familiar to the public. It will also instantly measure the performance of a lens based on the device on which it is mounted. More importantly, this measure is correlated with human vision perception of the picture quality and the definition can sometimes also be trapped in the distinction between resolution enhancement and impression of sharpness. This new measurement unit will therefore take into account all the criterias as well as lens optical defects lead to an overall score. DxO Labs would like this new measure to replace the MTF scores widely used in the industry today. I think that this approach goes in the right direction because it takes into account the human eye and run away from “science for science”.
We can now have have a lot of fun making comparisons more understandable and talking between couples camera-lens with the “perceptual megapixel” that can quantify the impact of the definition of the sensor and the intrinsic optical quality of the lens to achieve a perceived resolution. Thus, DxO Labs says that a Canon EOS 5D Mark III, with a 21 megapixel sensor, will give a perceived resolution of 17.2 megapixels with a Sigma 35mm F1.4 DG HSM against 15.2 megapixel with with a Zeiss Distagon T * 35mm f / 1.4 ZE.
With its database of 2700 profiled and measured camera+lens duets, DxO Labs advance an average loss of 45% of the potential of the camera because of the lens. That is the finding of the study that DxO is turning into a mind blowing announcement. Dear photographer friends, you lose 45% of your sensor’s megapixels because of the lens you use !
The recipe that DxOMark used to concoct the final “Perceptual Megapixel” score has not been disclosed yet but I’ll would like to take a look at it to check by myself how far we can trust DxO for the perceptual megapixel. All they said is that they worked wth some CNES findings on sattelite image quality enhacenement and analysis to achieve this….