Archived posting to the Leica Users Group, 2006/11/18
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Howard.. all I said was to put the "special recommended filter" ( my terms, not someone else's) in front of the sensor, not the lens... If the solution is to place a specific filter in front of the lens, move it just in front of the sensor......( as part of the coatings on the protector glass plate...) It is all part of the same optical chain..... If it works in front of the lens, it works in front of the sensor..... Did I read your response wrong? Or is the response from Leica BS? I am still not sure about the Leica story/fix..... Someone show me a test that proves the lens A has a magenta cast, but immediately putting the filter on, in the same scene, the magenta cast goes away..... ( it is not that I necessarily disbelieve Leica, but I would prefer to see proof....) Yes, you need it 100% of the time... or else be sure your image is cool.....and no one wears black... ( what will Kyle do with his Goths?) PS.. A reason the white balance is unaffected is that the WB sensor is not TTL.... PPS.. I do not understand paragraph 3.... which starts off....." In the first case, a separate..." Could you explain again? Frank Filippone red735i@earthlink.net Frank-- The fix is not as simple as a magenta-subtracting coating. If the problem were excessive sensitivity to a combination of visible wavelengths that causes a magenta cast in the final interpretation of the color balance, then that's basically irrelevant in an engineering sense. This is a fixed proportioning, in visible colors, of the differential responses of the individual pixels. It's just a matter of how the numbers of electrons in the wells corresponding to the R, G, and B pixels are interpreted in software. There are inherent inequalities in the detective quantum efficiency of the sensor at different wavelengths in the first place, and this differential efficiency has to be accounted for in the camera design, either in the particulars of the color filters over each pixel or in firmware processing of the signal. However, if I understand correctly, the problem is that infrared wavelengths, which are not perceived visually and are disregarded in any process of presentation of the final image (monitor, printer, etc.), are inappropriately detected by the photon-detecting elements in such proportions as to be interpreted as magenta. Thus the recommendation of an IR filter, because this problem is, in any rigorous or non-arbitrary way, impossible to fix in software. There is obviously no way for any algorithm to distinguish between those electrons in R, G, and B wells generated by photons of (visible) wavelengths that constitute the color perceived as magenta on the one hand and, on the other hand, those generated by IR wavelengths. And the admixture of IR to visible differs arbitrarily from point to point in any picture, just as the colors do, so it's not a matter of subtracting some constant in SW. In the first case, a separate "magenta-minus" filter or coating would be clumsy and completely unnecessary, and a software "fix" (not a fix, just a proper setting of engineering variables) no issue at all, either unnecessary because of filter selection, or trivial and inconsequential. In the second case, the addition of an IR-minus filter is the only rigorous solution, short of technology that results in sensors that are simply insensitive to invisible wavelengths like IR. Apparently it is not feasible to build IR rejection into the R/G/B pixel filters, as it is usual to build in this function as a plate in front of the sensor, but apparently this was optically not feasible in the case of the M8. Any software "fix" would be a compromise that risks having arbitrary elements, and this is why Leica recommends the inelegant filter solution. --howard On Nov 18, 2006, at 10:46 AM, Frank Filippone wrote: > In response to BD's email about the M8 magenta cast.... > > I think that in today's marketing and sales driven marketplace, > digital or not, shipping without bugs ( known or not) is uncommon. > You must meet certain deadlines. Bad as that is, it is reality. > > However, the fact that you must use a piece of glass in front of > your lens.... note the operative word here is MUST.... is > unacceptable. ( No, I am not starting problems, it is an > opinion). If the sensor is slightly more magenta sensitive, the > glass > protecting filter should have been coated to attenuate the magenta > rays. ( that is what the applied filter will be doing). It is a > matter of a coating on the glass plate. It does not require more > glass over the sensor, thicker glass, SW interventions, or other > "extras". It is a VERY thin layer of deposited vapor on the glass > cover plate. It takes an optical engineer a few hours to > compute, a manufacturing engineer a few hours to try it. It is not > brain surgery. > > It should have been done, it needs to be done, it is unacceptable > that it was not offered as the "fix", with free retrofitting to > early adopters. > > But Leica had to meet deadlines, and Leica does not want to be in > the business of sensor replacement. So it was not offered. > > Kodak did not screw up, Leica did. They should have tested the > sensor over the optical BW, found the error ( or they did find the > error and decided that the market would not find it or that it > would be fixed in SW) and offered to fix the issue in production > sensor glass cover plates. > > It is the only acceptable solution..... > > How many of the LUG have backgrounds in Technology and heard those > dreadful words... Fix it in ....SW? > > Frank Filippone > red735i@earthlink.net > > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information _______________________________________________ Leica Users Group. See http://leica-users.org/mailman/listinfo/lug for more information