smelni
10-31-2009, 01:12 PM
I first want to thank Barry G for his comprehensive rez test and alias article for the 7d - really informative
but i also want to throw a little curve ball here - very often resolution is not nearly as important to image quality as MTF. MTF measures the reproduction of different frequencies (number of lines per inch) throughout a video system.
Since the rez test on the 7d shows a dramatic falloff into aliasing at a certain (and fairly low) resolution, that doesnt mean that the resolution that it is reproducing isnt amazing (or that it is amazing for that matter)
think of it this way - if you are trying to reproduce many lines per inch, the 7d aliased and therefore will have a poor if not non existant mtf at that frequency. But not take a medium frequency (medium number of lines per inch) and how does it perform. This is a real important question and speaks to the actual curve of the mtf for this camera system. The optical low pass filter is usually tuned to the curve on the mtf to cut off information when the mtf is so low that is should be reproduced as grey instead of aliasing occuring. We know that the 7d doesnt have a well placed OLPF for video. But how does the mtf curve behave before that point.
WHY in the world am I bringing this up. Well, lots of people are asking why the images looks so damn good, and everyone loves the images, and compliments all around - yet the camera has shown to have less the HD rez. The mtf MIGHT (I dont know) explain this. Perhaps the curve is so well shaped before frequencies at which aliasing occur that the image looks amazing EXCEPT For high frequency detail. PERHAPS the mid and low level detail are being so accurately rendered that it looks amazing.
I am going to try to run some mtf tests on the camera but I cant promise when - but if anyone has the capability of measuring the 7d mtf vs a "real" HD camera that would be great. I predict that we might see why the image from the camera is so pleasing even though rez tests arent having great results.
but i also want to throw a little curve ball here - very often resolution is not nearly as important to image quality as MTF. MTF measures the reproduction of different frequencies (number of lines per inch) throughout a video system.
Since the rez test on the 7d shows a dramatic falloff into aliasing at a certain (and fairly low) resolution, that doesnt mean that the resolution that it is reproducing isnt amazing (or that it is amazing for that matter)
think of it this way - if you are trying to reproduce many lines per inch, the 7d aliased and therefore will have a poor if not non existant mtf at that frequency. But not take a medium frequency (medium number of lines per inch) and how does it perform. This is a real important question and speaks to the actual curve of the mtf for this camera system. The optical low pass filter is usually tuned to the curve on the mtf to cut off information when the mtf is so low that is should be reproduced as grey instead of aliasing occuring. We know that the 7d doesnt have a well placed OLPF for video. But how does the mtf curve behave before that point.
WHY in the world am I bringing this up. Well, lots of people are asking why the images looks so damn good, and everyone loves the images, and compliments all around - yet the camera has shown to have less the HD rez. The mtf MIGHT (I dont know) explain this. Perhaps the curve is so well shaped before frequencies at which aliasing occur that the image looks amazing EXCEPT For high frequency detail. PERHAPS the mid and low level detail are being so accurately rendered that it looks amazing.
I am going to try to run some mtf tests on the camera but I cant promise when - but if anyone has the capability of measuring the 7d mtf vs a "real" HD camera that would be great. I predict that we might see why the image from the camera is so pleasing even though rez tests arent having great results.