spalbird
Senior Member
Yes, but I suggest to acquire knowledge better from sb already mastered the basics, please not from me. Oversampling in audio has another reason and without knowing the facts (cost and effort reasons, marketed as a superior improvement to the crowd) should not be used as an argument here...
Whether an antiliasing filter is needed or not, everybody can decide by himself on hard facts, much more accurate than anybody else can do for him: Look at the picture, if there are no disturbing artefacts an antialiasing filter was not needed, if there are, the lack of an antialiasing filter has impaired the picture.
The observation of many people here is, that the AA filter has an impact on the majority of the Bayer pictures, and they dislike it. Milling down the AA filter on Bayer cameras gives better results for some enthusiasts. In the professional field the Hasselblads etc. are delivered w/o AA filter, if required it can be used as an option. The Leica Digital Modul R, the Leica M series as well as the Leica S2 does not utilize an AA filter.
One of the main reasons to use AA filters with Bayer cameras is, that the red and blue channel does degrade already at lower frequencies compared to the green channel, there are 2x more green pixels available than red or blue. This can become visible as very distractive color aliasing. The Foveon sensor has all color information for every pixel and therefore does not show this effect. Even if aliasing occurs, there is no color aliasing on Foveon pictures. Color aliasing is ways more disturbing.
For the same picture and lens, the aliasing artefacts will be higher for a sensor with less pixels. Contrary to random noise characterised by the same power for all frequencies real life pictures are bandlimited and carry less power for the higher frequencies. For our eye the residual errors are oven more than acceptable.
Concerning this, our ear is much more sensitive compared to our eye. Our ear can separate higher and lower frequencies very well. Aliasing in the audio field appears as additional single tones or "digital noise" which tends to make instruments sound harsh. In the analoge age another necessisity for an audio amplifier was discovered - the linearity. If a signal is amplified by the same factor for all levels no distortion occures. Nonlinearities produce additional frequency components at multiples of the base frequency. The difference between the tube amps and transistor amps is that distortions for the tube are at hamonics (even freq), contrary the transistor's distortions adds uneven and therefore alien frequency components to real instruments. (For the same reason tube amps are used for electric guitars with the attention to add harmonic distortion to the signal). Another unwanted effect is hard clipping of the signal.
So, why this journey into the audio field? Damnd, who cares about linearity in digital picture processing? Now as we know that non-linearity adds new frequencies to the real signal, we should not want this. The truth is, it does not become visible to our eye, and the first what we do is no manipulate curves by adjusting the light temperature, the contrast and brightness, and do other manipulations for each color, then sharpen the image, adapt the color room!!! For nonlinear editing we use a lot of money and time while in the audio world a lot of money is spent for equipment which only transports the signal, and does not add or take off something from it.
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