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#1
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Digital quality (vs 35mm): Any real answers?
Hi.
I'm still wondering about how good the image quality of modern digital cameras (especially SLRs) really is, in particular how it compares with 35mm film. I've seen many articles on the subject on the Net, but few of them seem to give you a lot of tangible information (I want to see the numbers, please), and I can't help feeling that tests they refer to are usually done to prove a point, i.e. that digital cameras are as good as 35mm, which is not the way you do proper research. To say a few words about myself, I'm working for a company that makes high-accuracy, large-format scanners, so I'm not particularly impressed when I hear e.g 6 million pixels (you need to talk about *billions* of pixels if I'm really going to listen), and the word "interpolation" leaves a bad taste in my mouth. But this also means I know that high resolution isn't everything, of course; parameters like geometric precision or signal-to-noise ratio also count a lot. Be that as it may, some of the questions I'd like to have answered are these: 1. What is the resolution of a 35mm film anyway? I think I read somewhere that a colour negative is at least 3000dpi. Is that correct? How about black&white? (Yeah I know, a film doesn't have pixels in exactly the same sense as a digital image, but it *is* made up of discrete elements after all.) 2. What about the print? 300dpi? 3. I know that the most common sensors are made up of individual elements for the read, green and blue channels, arranged in a special pattern, whose data is somehow interpolated into RGB pixels. But what exactly does e.g. 6 megapixels mean in that context? Does it mean that the sensor has (just) 6 million elements, or that data from a higher number (like 18 or 24 million) is combined into 6 million RGB pixels? The same question more bluntly put: When Canon/Nikon/Pentax is talking about 6MP, is that just a big a lie as the one about 10MP on Sigma cameras? (I'm hoping not, as I think the Sigma/Foveon way of counting really takes the cake.) 4. Can the inaccuracy associated with the above mentioned interpolation be quantified and/or measured against e.g. the error introduced by scanning a negative with a film-scanner? And how does it compare with pixel interpolation in the scanning sense? 5. And how about those other parameters I mentioned briefly above - like different kinds of geometric distortions, noise, flat field bias etc.? Can those be compared with the ones of plain old film? 6. And the chromic aberration effects? How serious are they these days? And are the full-frame sensors that are actually found in some high-end cameras now, in any way comparable to film in that respect? Well, maybe some people will say I have a somewhat critical or conservative attitude towards digital cameras, but I actually think you ought to be a bit sceptical when something "new and wonderful" comes a long; new technology is too often introduced for technology's own sake, IMO. - Toralf |
#2
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Digital quality (vs 35mm): Any real answers?
Toralf wrote:
I'm still wondering about how good the image quality of modern digital cameras (especially SLRs) really is, in particular how it compares with 35mm film. I've seen many articles on the subject on the Net, but few of them seem to give you a lot of tangible information (I want to see the numbers, please), and I can't help feeling that tests they refer to are usually done to prove a point, i.e. that digital cameras are as good as 35mm, which is not the way you do proper research. To say a few words about myself, I'm working for a company that makes high-accuracy, large-format scanners, so I'm not particularly impressed when I hear e.g 6 million pixels (you need to talk about *billions* of pixels if I'm really going to listen), and the word "interpolation" leaves a bad taste in my mouth. But this also means I know that high resolution isn't everything, of course; parameters like geometric precision or signal-to-noise ratio also count a lot. ..... Why not convince yourself (one way or the other) by comparing side-by-side prints (or whatever final output you like) of 35mm prints/scans and 6MP DSLR. I viewed some 20" X 30" prints from a 6PM digital, bought one, sold my film bodies and haven't regreted it. YMMV -Dave |
#3
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Digital quality (vs 35mm): Any real answers?
Toralf wrote:
I'm still wondering about how good the image quality of modern digital cameras (especially SLRs) really is, in particular how it compares with 35mm film. I've seen many articles on the subject on the Net, but few of them seem to give you a lot of tangible information (I want to see the numbers, please), and I can't help feeling that tests they refer to are usually done to prove a point, i.e. that digital cameras are as good as 35mm, which is not the way you do proper research. To say a few words about myself, I'm working for a company that makes high-accuracy, large-format scanners, so I'm not particularly impressed when I hear e.g 6 million pixels (you need to talk about *billions* of pixels if I'm really going to listen), and the word "interpolation" leaves a bad taste in my mouth. But this also means I know that high resolution isn't everything, of course; parameters like geometric precision or signal-to-noise ratio also count a lot. ..... Why not convince yourself (one way or the other) by comparing side-by-side prints (or whatever final output you like) of 35mm prints/scans and 6MP DSLR. I viewed some 20" X 30" prints from a 6PM digital, bought one, sold my film bodies and haven't regreted it. YMMV -Dave |
#4
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Digital quality (vs 35mm): Any real answers?
OK, I'll take a shot at it...
It used to be "Film is cheap,' now it's "Cameras are cheap." 1. What is the resolution of a 35mm film anyway? - For practical purposes, it's infinite. 2. What about the print? 300dpi - Unless you're printing posters, it's not relevant. 3. exactly does e.g. 6 megapixels mean - 6.3 megapixels is 6,291,456 sensors. 4. Can the inaccuracy associated with the above mentioned interpolation be measured - Film will almost always be better, but it's what the outside eyes see that matters. 5. geometric distortions, noise, flat field bias etc. - That's a lens issues, not sensor/film issues 6. And the chromic aberration effects? - As far as I know, all digicams are prone to purple fringing, which is something you don't see on any cheap slr. My two cents worth. Hi. I'm still wondering about how good the image quality of modern digital cameras (especially SLRs) really is, in particular how it compares with 35mm film. I've seen many articles on the subject on the Net, but few of them seem to give you a lot of tangible information (I want to see the numbers, please), and I can't help feeling that tests they refer to are usually done to prove a point, i.e. that digital cameras are as good as 35mm, which is not the way you do proper research. To say a few words about myself, I'm working for a company that makes high-accuracy, large-format scanners, so I'm not particularly impressed when I hear e.g 6 million pixels (you need to talk about *billions* of pixels if I'm really going to listen), and the word "interpolation" leaves a bad taste in my mouth. But this also means I know that high resolution isn't everything, of course; parameters like geometric precision or signal-to-noise ratio also count a lot. Be that as it may, some of the questions I'd like to have answered are these: 1. What is the resolution of a 35mm film anyway? I think I read somewhere that a colour negative is at least 3000dpi. Is that correct? How about black&white? (Yeah I know, a film doesn't have pixels in exactly the same sense as a digital image, but it *is* made up of discrete elements after all.) 2. What about the print? 300dpi? 3. I know that the most common sensors are made up of individual elements for the read, green and blue channels, arranged in a special pattern, whose data is somehow interpolated into RGB pixels. But what exactly does e.g. 6 megapixels mean in that context? Does it mean that the sensor has (just) 6 million elements, or that data from a higher number (like 18 or 24 million) is combined into 6 million RGB pixels? The same question more bluntly put: When Canon/Nikon/Pentax is talking about 6MP, is that just a big a lie as the one about 10MP on Sigma cameras? (I'm hoping not, as I think the Sigma/Foveon way of counting really takes the cake.) 4. Can the inaccuracy associated with the above mentioned interpolation be quantified and/or measured against e.g. the error introduced by scanning a negative with a film-scanner? And how does it compare with pixel interpolation in the scanning sense? 5. And how about those other parameters I mentioned briefly above - like different kinds of geometric distortions, noise, flat field bias etc.? Can those be compared with the ones of plain old film? 6. And the chromic aberration effects? How serious are they these days? And are the full-frame sensors that are actually found in some high-end cameras now, in any way comparable to film in that respect? Well, maybe some people will say I have a somewhat critical or conservative attitude towards digital cameras, but I actually think you ought to be a bit sceptical when something "new and wonderful" comes a long; new technology is too often introduced for technology's own sake, IMO. - Toralf |
#5
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Digital quality (vs 35mm): Any real answers?
OK, I'll take a shot at it...
It used to be "Film is cheap,' now it's "Cameras are cheap." 1. What is the resolution of a 35mm film anyway? - For practical purposes, it's infinite. 2. What about the print? 300dpi - Unless you're printing posters, it's not relevant. 3. exactly does e.g. 6 megapixels mean - 6.3 megapixels is 6,291,456 sensors. 4. Can the inaccuracy associated with the above mentioned interpolation be measured - Film will almost always be better, but it's what the outside eyes see that matters. 5. geometric distortions, noise, flat field bias etc. - That's a lens issues, not sensor/film issues 6. And the chromic aberration effects? - As far as I know, all digicams are prone to purple fringing, which is something you don't see on any cheap slr. My two cents worth. Hi. I'm still wondering about how good the image quality of modern digital cameras (especially SLRs) really is, in particular how it compares with 35mm film. I've seen many articles on the subject on the Net, but few of them seem to give you a lot of tangible information (I want to see the numbers, please), and I can't help feeling that tests they refer to are usually done to prove a point, i.e. that digital cameras are as good as 35mm, which is not the way you do proper research. To say a few words about myself, I'm working for a company that makes high-accuracy, large-format scanners, so I'm not particularly impressed when I hear e.g 6 million pixels (you need to talk about *billions* of pixels if I'm really going to listen), and the word "interpolation" leaves a bad taste in my mouth. But this also means I know that high resolution isn't everything, of course; parameters like geometric precision or signal-to-noise ratio also count a lot. Be that as it may, some of the questions I'd like to have answered are these: 1. What is the resolution of a 35mm film anyway? I think I read somewhere that a colour negative is at least 3000dpi. Is that correct? How about black&white? (Yeah I know, a film doesn't have pixels in exactly the same sense as a digital image, but it *is* made up of discrete elements after all.) 2. What about the print? 300dpi? 3. I know that the most common sensors are made up of individual elements for the read, green and blue channels, arranged in a special pattern, whose data is somehow interpolated into RGB pixels. But what exactly does e.g. 6 megapixels mean in that context? Does it mean that the sensor has (just) 6 million elements, or that data from a higher number (like 18 or 24 million) is combined into 6 million RGB pixels? The same question more bluntly put: When Canon/Nikon/Pentax is talking about 6MP, is that just a big a lie as the one about 10MP on Sigma cameras? (I'm hoping not, as I think the Sigma/Foveon way of counting really takes the cake.) 4. Can the inaccuracy associated with the above mentioned interpolation be quantified and/or measured against e.g. the error introduced by scanning a negative with a film-scanner? And how does it compare with pixel interpolation in the scanning sense? 5. And how about those other parameters I mentioned briefly above - like different kinds of geometric distortions, noise, flat field bias etc.? Can those be compared with the ones of plain old film? 6. And the chromic aberration effects? How serious are they these days? And are the full-frame sensors that are actually found in some high-end cameras now, in any way comparable to film in that respect? Well, maybe some people will say I have a somewhat critical or conservative attitude towards digital cameras, but I actually think you ought to be a bit sceptical when something "new and wonderful" comes a long; new technology is too often introduced for technology's own sake, IMO. - Toralf |
#6
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Digital quality (vs 35mm): Any real answers?
All the tests I have seen where 35mm film is compared to a modern DSLR
(6-11MP)...the DSLR pictures shows more detail and less noise than a fine grained film like Provia 100F. It is quite fustrating that 6MP can beat 35mm. I know many scanners can do 4000 dpi but if most of the information is noise? I still use film and it will be quite interresting to see a test where e.g. Provia 100F shows more detail than an e.g. D1X/D70 or 1Ds/300D. When I see my slides projected it seems strange that a 6MP DSLR can do better.... Max "Toralf" skrev i en meddelelse ... Hi. I'm still wondering about how good the image quality of modern digital cameras (especially SLRs) really is, in particular how it compares with 35mm film. I've seen many articles on the subject on the Net, but few of them seem to give you a lot of tangible information (I want to see the numbers, please), and I can't help feeling that tests they refer to are usually done to prove a point, i.e. that digital cameras are as good as 35mm, which is not the way you do proper research. To say a few words about myself, I'm working for a company that makes high-accuracy, large-format scanners, so I'm not particularly impressed when I hear e.g 6 million pixels (you need to talk about *billions* of pixels if I'm really going to listen), and the word "interpolation" leaves a bad taste in my mouth. But this also means I know that high resolution isn't everything, of course; parameters like geometric precision or signal-to-noise ratio also count a lot. Be that as it may, some of the questions I'd like to have answered are these: 1. What is the resolution of a 35mm film anyway? I think I read somewhere that a colour negative is at least 3000dpi. Is that correct? How about black&white? (Yeah I know, a film doesn't have pixels in exactly the same sense as a digital image, but it *is* made up of discrete elements after all.) 2. What about the print? 300dpi? 3. I know that the most common sensors are made up of individual elements for the read, green and blue channels, arranged in a special pattern, whose data is somehow interpolated into RGB pixels. But what exactly does e.g. 6 megapixels mean in that context? Does it mean that the sensor has (just) 6 million elements, or that data from a higher number (like 18 or 24 million) is combined into 6 million RGB pixels? The same question more bluntly put: When Canon/Nikon/Pentax is talking about 6MP, is that just a big a lie as the one about 10MP on Sigma cameras? (I'm hoping not, as I think the Sigma/Foveon way of counting really takes the cake.) 4. Can the inaccuracy associated with the above mentioned interpolation be quantified and/or measured against e.g. the error introduced by scanning a negative with a film-scanner? And how does it compare with pixel interpolation in the scanning sense? 5. And how about those other parameters I mentioned briefly above - like different kinds of geometric distortions, noise, flat field bias etc.? Can those be compared with the ones of plain old film? 6. And the chromic aberration effects? How serious are they these days? And are the full-frame sensors that are actually found in some high-end cameras now, in any way comparable to film in that respect? Well, maybe some people will say I have a somewhat critical or conservative attitude towards digital cameras, but I actually think you ought to be a bit sceptical when something "new and wonderful" comes a long; new technology is too often introduced for technology's own sake, IMO. - Toralf |
#7
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Digital quality (vs 35mm): Any real answers?
A 2MP DSLR often does better than a 35mm camera because the depth
of field is so much greater for the tiny focal length lens. Another thing you might ask is how many pixels are you actually using in your eye? If you only have 2MP in the area that the photo is in your visual range it no longer matters if there are 2 or 200MP. And unless you take your film to a professional photo lab the processing lab will likely print it out of focus anyway. The net result is I find even my 5 year old 2MP camera delivers sharper pictures than my pile of 35mm equipment does. "MXP" wrote in message . .. All the tests I have seen where 35mm film is compared to a modern DSLR (6-11MP)...the DSLR pictures shows more detail and less noise than a fine grained film like Provia 100F. It is quite fustrating that 6MP can beat 35mm. I know many scanners can do 4000 dpi but if most of the information is noise? I still use film and it will be quite interresting to see a test where e.g. Provia 100F shows more detail than an e.g. D1X/D70 or 1Ds/300D. When I see my slides projected it seems strange that a 6MP DSLR can do better.... Max "Toralf" skrev i en meddelelse ... Hi. I'm still wondering about how good the image quality of modern digital cameras (especially SLRs) really is, in particular how it compares with 35mm film. I've seen many articles on the subject on the Net, but few of them seem to give you a lot of tangible information (I want to see the numbers, please), and I can't help feeling that tests they refer to are usually done to prove a point, i.e. that digital cameras are as good as 35mm, which is not the way you do proper research. To say a few words about myself, I'm working for a company that makes high-accuracy, large-format scanners, so I'm not particularly impressed when I hear e.g 6 million pixels (you need to talk about *billions* of pixels if I'm really going to listen), and the word "interpolation" leaves a bad taste in my mouth. But this also means I know that high resolution isn't everything, of course; parameters like geometric precision or signal-to-noise ratio also count a lot. Be that as it may, some of the questions I'd like to have answered are these: 1. What is the resolution of a 35mm film anyway? I think I read somewhere that a colour negative is at least 3000dpi. Is that correct? How about black&white? (Yeah I know, a film doesn't have pixels in exactly the same sense as a digital image, but it *is* made up of discrete elements after all.) 2. What about the print? 300dpi? 3. I know that the most common sensors are made up of individual elements for the read, green and blue channels, arranged in a special pattern, whose data is somehow interpolated into RGB pixels. But what exactly does e.g. 6 megapixels mean in that context? Does it mean that the sensor has (just) 6 million elements, or that data from a higher number (like 18 or 24 million) is combined into 6 million RGB pixels? The same question more bluntly put: When Canon/Nikon/Pentax is talking about 6MP, is that just a big a lie as the one about 10MP on Sigma cameras? (I'm hoping not, as I think the Sigma/Foveon way of counting really takes the cake.) 4. Can the inaccuracy associated with the above mentioned interpolation be quantified and/or measured against e.g. the error introduced by scanning a negative with a film-scanner? And how does it compare with pixel interpolation in the scanning sense? 5. And how about those other parameters I mentioned briefly above - like different kinds of geometric distortions, noise, flat field bias etc.? Can those be compared with the ones of plain old film? 6. And the chromic aberration effects? How serious are they these days? And are the full-frame sensors that are actually found in some high-end cameras now, in any way comparable to film in that respect? Well, maybe some people will say I have a somewhat critical or conservative attitude towards digital cameras, but I actually think you ought to be a bit sceptical when something "new and wonderful" comes a long; new technology is too often introduced for technology's own sake, IMO. - Toralf |
#8
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Digital quality (vs 35mm): Any real answers?
Toralf writes:
Hi. I'm still wondering about how good the image quality of modern digital cameras (especially SLRs) really is, in particular how it compares with 35mm film. I've seen many articles on the subject on the Net, but few of them seem to give you a lot of tangible information (I want to see the numbers, please), and I can't help feeling that tests they refer to are usually done to prove a point, i.e. that digital cameras are as good as 35mm, which is not the way you do proper research. To say a few words about myself, I'm working for a company that makes high-accuracy, large-format scanners, so I'm not particularly impressed when I hear e.g 6 million pixels (you need to talk about *billions* of pixels if I'm really going to listen), and the word "interpolation" leaves a bad taste in my mouth. But this also means I know that high resolution isn't everything, of course; parameters like geometric precision or signal-to-noise ratio also count a lot. Be that as it may, some of the questions I'd like to have answered are these: 1. What is the resolution of a 35mm film anyway? It's hard to say, as the resolution limit is different from that of a digital sensor. Rather than a hard limit, you get less information and more blur and noise as you increase resolution in scanning a piece of film. I think I read somewhere that a colour negative is at least 3000dpi. Is that correct? It's in the ballpark. The data sheet I have for Provia 100F shows an MTF of 35% or so at 50 cycles/mm. That corresponds. to 100 samples/mm, which is 2540 dpi. You presumably know what MTF means, but for others who may be reading, that says that if you image a sine-wave grating onto this film at a frequency of 50 cycles per millimeter, you will get about 35% of the contrast back from the film. But then what comes out of the lens will be reduced in contrast from what was in the envirnoment, so it's on the ragged edge of what you might really hope to reproduce. The MTF for Ektachrome 100 Pro is right at 30% at 50 c/mm. Kodachrome 64 is about the same, and Kodachrome 25 is about 35%. How about black&white? Well, the data sheet on Kodak Technical Pan, which is an extreme upper bound, has MTF at 50% at 180 c/mm or so. That's for ISO 25, developed in Technidol. That's Kodak Tech Pub P-255, available at http://www.kodak.com/global/en/professional/support/techPubs/p255/p255.jhtml?id=0.1.18.14.21.22.16&lc=en. For Plus-X, at ISO 125, Tech Pub F-4018 (at http://www.kodak.com/global/en/professional/support/techPubs/f4018/f4018.jhtml?id=0.1.18.14.21.20.16&lc=en) rates it at 50 lp/mm at 1.6:1 contrast, 125 at 1000:1 (which you aren't likely to reach it practice). So I think we can say that scanning film at more than, say, 360 samples/mm (about 9,000 samples/inch) is pretty much useless. In most circumstances, 100 samples/mm or 2,540 /inch is plenty. So we're in the region of 9MP for a normal 24x36mm 35mm film frame. (Yeah I know, a film doesn't have pixels in exactly the same sense as a digital image, but it *is* made up of discrete elements after all.) But they aren't spaced on a regular grid, so things look a lot different. 2. What about the print? 300dpi? Well, there are lots of variables involved there. One of the little secrets that the "film-only" zealots don't seem to mention is that to view the film, it must either be scanned, projected, or printed. I have heard the claim that scanning digitally loses quality, but so do the other two processes. How good are the optics in your enlarger or slide projector? How perfectly is either one focused? I really don't know what sort of degredation is involved, but it seems that it might be on the same order as through the camera optics, or worse. And lens MTF's usually aren't quoted beyond 40 cycles/mm! Check the Zeiss or Canon Web sites if you don't believe me. 3. I know that the most common sensors are made up of individual elements for the red, green and blue channels, arranged in a special pattern, whose data is somehow interpolated into RGB pixels. But what exactly does e.g. 6 megapixels mean in that context? Does it mean that the sensor has (just) 6 million elements, or that data from a higher number (like 18 or 24 million) is combined into 6 million RGB pixels? The former. Except for the Foveon sensor in the Sigma SD9/SD10, which has about 3.5 million sites, each of which detects all three channels. The same question more bluntly put: When Canon/Nikon/Pentax is talking about 6MP, is that just a big a lie as the one about 10MP on Sigma cameras? (I'm hoping not, as I think the Sigma/Foveon way of counting really takes the cake.) 4. Can the inaccuracy associated with the above mentioned interpolation be quantified and/or measured against e.g. the error introduced by scanning a negative with a film-scanner? And how does it compare with pixel interpolation in the scanning sense? Not really. The reality is that sensing all channels at each location is a Good Thing, other factors being equal, but the color filter array isn't as bad as you might think. First of all, the three color channels aren't completely uncorrelated, so the information from a red sensel can be used to help estimate the red and green values at that point. Second, images have some sort of spatial structure, and modern demosaicing algorithms try to detect that to deduce missing values. Finally, the sampling rate is higher for the green channel, to which the human visual system is most sensitive, both in luminance and resolution. 5. And how about those other parameters I mentioned briefly above - like different kinds of geometric distortions, noise, flat field bias etc.? Can those be compared with the ones of plain old film? Yup. Lots of them are only being noticed now with digital sensors behind the same lenses that people have used for years with film. I suspect that it's a matter of display more than anything else; the magnification on screen at a 1:1 pixel magnification is huge for most cameras, and people can use the little eyedropper to see just how much the illumination falls off in the corner of the frame. 6. And the chromic aberration effects? How serious are they these days? And are the full-frame sensors that are actually found in some high-end cameras now, in any way comparable to film in that respect? Chromatic aberration is basically in the lens. Doesn't matter what sensor is behind it. Well, maybe some people will say I have a somewhat critical or conservative attitude towards digital cameras, but I actually think you ought to be a bit sceptical when something "new and wonderful" comes a long; new technology is too often introduced for technology's own sake, IMO. Oh, sure. But there are a number of photographers who are putting away their 4.5x6 film cameras because they see better quality out of the Kodak DCS 14 MP cameras. In a functional way, the best digitals are pretty good, though their limitations are different from those of film cameras. -- -Stephen H. Westin Any information or opinions in this message are mine: they do not represent the position of Cornell University or any of its sponsors. |
#9
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Digital quality (vs 35mm): Any real answers?
Toralf writes:
Hi. I'm still wondering about how good the image quality of modern digital cameras (especially SLRs) really is, in particular how it compares with 35mm film. I've seen many articles on the subject on the Net, but few of them seem to give you a lot of tangible information (I want to see the numbers, please), and I can't help feeling that tests they refer to are usually done to prove a point, i.e. that digital cameras are as good as 35mm, which is not the way you do proper research. To say a few words about myself, I'm working for a company that makes high-accuracy, large-format scanners, so I'm not particularly impressed when I hear e.g 6 million pixels (you need to talk about *billions* of pixels if I'm really going to listen), and the word "interpolation" leaves a bad taste in my mouth. But this also means I know that high resolution isn't everything, of course; parameters like geometric precision or signal-to-noise ratio also count a lot. Be that as it may, some of the questions I'd like to have answered are these: 1. What is the resolution of a 35mm film anyway? It's hard to say, as the resolution limit is different from that of a digital sensor. Rather than a hard limit, you get less information and more blur and noise as you increase resolution in scanning a piece of film. I think I read somewhere that a colour negative is at least 3000dpi. Is that correct? It's in the ballpark. The data sheet I have for Provia 100F shows an MTF of 35% or so at 50 cycles/mm. That corresponds. to 100 samples/mm, which is 2540 dpi. You presumably know what MTF means, but for others who may be reading, that says that if you image a sine-wave grating onto this film at a frequency of 50 cycles per millimeter, you will get about 35% of the contrast back from the film. But then what comes out of the lens will be reduced in contrast from what was in the envirnoment, so it's on the ragged edge of what you might really hope to reproduce. The MTF for Ektachrome 100 Pro is right at 30% at 50 c/mm. Kodachrome 64 is about the same, and Kodachrome 25 is about 35%. How about black&white? Well, the data sheet on Kodak Technical Pan, which is an extreme upper bound, has MTF at 50% at 180 c/mm or so. That's for ISO 25, developed in Technidol. That's Kodak Tech Pub P-255, available at http://www.kodak.com/global/en/professional/support/techPubs/p255/p255.jhtml?id=0.1.18.14.21.22.16&lc=en. For Plus-X, at ISO 125, Tech Pub F-4018 (at http://www.kodak.com/global/en/professional/support/techPubs/f4018/f4018.jhtml?id=0.1.18.14.21.20.16&lc=en) rates it at 50 lp/mm at 1.6:1 contrast, 125 at 1000:1 (which you aren't likely to reach it practice). So I think we can say that scanning film at more than, say, 360 samples/mm (about 9,000 samples/inch) is pretty much useless. In most circumstances, 100 samples/mm or 2,540 /inch is plenty. So we're in the region of 9MP for a normal 24x36mm 35mm film frame. (Yeah I know, a film doesn't have pixels in exactly the same sense as a digital image, but it *is* made up of discrete elements after all.) But they aren't spaced on a regular grid, so things look a lot different. 2. What about the print? 300dpi? Well, there are lots of variables involved there. One of the little secrets that the "film-only" zealots don't seem to mention is that to view the film, it must either be scanned, projected, or printed. I have heard the claim that scanning digitally loses quality, but so do the other two processes. How good are the optics in your enlarger or slide projector? How perfectly is either one focused? I really don't know what sort of degredation is involved, but it seems that it might be on the same order as through the camera optics, or worse. And lens MTF's usually aren't quoted beyond 40 cycles/mm! Check the Zeiss or Canon Web sites if you don't believe me. 3. I know that the most common sensors are made up of individual elements for the red, green and blue channels, arranged in a special pattern, whose data is somehow interpolated into RGB pixels. But what exactly does e.g. 6 megapixels mean in that context? Does it mean that the sensor has (just) 6 million elements, or that data from a higher number (like 18 or 24 million) is combined into 6 million RGB pixels? The former. Except for the Foveon sensor in the Sigma SD9/SD10, which has about 3.5 million sites, each of which detects all three channels. The same question more bluntly put: When Canon/Nikon/Pentax is talking about 6MP, is that just a big a lie as the one about 10MP on Sigma cameras? (I'm hoping not, as I think the Sigma/Foveon way of counting really takes the cake.) 4. Can the inaccuracy associated with the above mentioned interpolation be quantified and/or measured against e.g. the error introduced by scanning a negative with a film-scanner? And how does it compare with pixel interpolation in the scanning sense? Not really. The reality is that sensing all channels at each location is a Good Thing, other factors being equal, but the color filter array isn't as bad as you might think. First of all, the three color channels aren't completely uncorrelated, so the information from a red sensel can be used to help estimate the red and green values at that point. Second, images have some sort of spatial structure, and modern demosaicing algorithms try to detect that to deduce missing values. Finally, the sampling rate is higher for the green channel, to which the human visual system is most sensitive, both in luminance and resolution. 5. And how about those other parameters I mentioned briefly above - like different kinds of geometric distortions, noise, flat field bias etc.? Can those be compared with the ones of plain old film? Yup. Lots of them are only being noticed now with digital sensors behind the same lenses that people have used for years with film. I suspect that it's a matter of display more than anything else; the magnification on screen at a 1:1 pixel magnification is huge for most cameras, and people can use the little eyedropper to see just how much the illumination falls off in the corner of the frame. 6. And the chromic aberration effects? How serious are they these days? And are the full-frame sensors that are actually found in some high-end cameras now, in any way comparable to film in that respect? Chromatic aberration is basically in the lens. Doesn't matter what sensor is behind it. Well, maybe some people will say I have a somewhat critical or conservative attitude towards digital cameras, but I actually think you ought to be a bit sceptical when something "new and wonderful" comes a long; new technology is too often introduced for technology's own sake, IMO. Oh, sure. But there are a number of photographers who are putting away their 4.5x6 film cameras because they see better quality out of the Kodak DCS 14 MP cameras. In a functional way, the best digitals are pretty good, though their limitations are different from those of film cameras. -- -Stephen H. Westin Any information or opinions in this message are mine: they do not represent the position of Cornell University or any of its sponsors. |
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Digital quality (vs 35mm): Any real answers?
nitzsche writes:
OK, I'll take a shot at it... It used to be "Film is cheap,' now it's "Cameras are cheap." 1. What is the resolution of a 35mm film anyway? - For practical purposes, it's infinite. Not in this universe. For practical purposes, it's somewhere between 30-75 cycles/mm, most of the time. snip -- -Stephen H. Westin Any information or opinions in this message are mine: they do not represent the position of Cornell University or any of its sponsors. |
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