Quoting Nenad Djurdjevic <[EMAIL PROTECTED]>: > I am sure this question has been asked before but what would be the > megapixel equivalent of a 35mm colour slide? I have heard about 9 > megapixels. Anyone know any better? > >
Please someone correct me if I have got this wrong; I'm going to attempt a coherent (don't laugh) description of my own understanding here... IMO, the number of pixels can be considered to be a function of 1. the properties of the CCD used to capture the light, and 2. the software to interprete the captured data. I'm not sure I know all the properties involved, but at least there is the number of physical pixels, and their size (density), and the Bayer algorithm involved to reconstruct a colour image from the physical pixels. To consider a 35mm equivalent, assume a 36x24mm CCD. How many pixels do we have to put into a 36x24mm CCD to match the resolution power of a film? For simplicity, let's assume that this is equal to the size of film grains that we can measure in a microscope. When that is known (i haven't got the number...), we can compare that to the pixel size on the chip. I am pretty sure that eg. Provia 100F grain size is smaller than current pixel size in eg. *istD. And here's a problem; there is a physical limit to how small pixels can be before they start to behave erratically. The size used in the *istD is thought to be quite optimal, if I have understood this right. If the above is correct, the optimal 36x24mm CCD is one with approximately the same pixel density as the *istD has, which would amount to ca. 14 Megapixels. I don't know if 14 Megapixels in 36x24mm is even close to the grain size of ProviaF, but let's assume that it was...:-) Those 14 Mpix must be subjectet to Bayer interpolation before we can see a true RGB image. The interpolation will tend to smooth out details that are smaller than the smallest cluster of pixels used in the interpolation. I'm not sure exatly how this affects the final image quality, but I suspect that this is the reason why skin tones and blue skies look smoother with digital, while grassy fields or tree branches and twigs look smeared out. Especially in low-contrast situations. So, even if 14 Mpix was equivalent to film grain number, CCDs would be less able to hold detail (I think this is where the Foveon concept excels over Bayer interpolation). This means that you would need more pixels per area than you have film grain per area to record the same level of detail. If film grains can be made smaller than CCD pixels, film will win hands down. And that's no matter what format you compare. Another discussion is whether the lenses exist to give you full value for either recording media. If the practical resolving power is less than pixel/grain density, the difference between film and CCDs is suddenly not _that_ important any more. So Nenad, I'm not at all sure I know any better than you, I'd rather learn than teach. I'm just testing my own grip...:-) Cheers, Jostein ---------------------------------------------------------------- This message was sent using IMP, the Internet Messaging Program.
