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#51
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Could you actually see photos made from RAW files?
On Wed, 03 Jun 2009 11:51:59 +1000, Bob Larter
wrote: Eric Stevens wrote: On Tue, 02 Jun 2009 02:09:19 -0800, (Floyd L. Davidson) wrote: [...] The definition of "analog" is that the signal (in this case it would be the output signal from the sensor) is continuously variable (it has an infinite number of possible values). If it is "digital" then it must have a finite set of discrete values. (Note that the two definitions are together all inclusive and are mutually exclusive. Everything is either one or the other and nothing can be both.) Haw. You are now claiming that it is possible to have a continuously variable number of electrons. I maintain the number of electrons can only be represented by integers. By that exact same logic, resistors capacitors & transistors should be called "digital" devices, but they aren't. The industry definition of "digital" is something that only works with binary levels. Everything else is called "analog". References: http://en.wikipedia.org/wiki/Digital_electronics "In a digital circuit, a signal is represented in discrete states or logic levels." - but they don't have to be binary. http://en.wikipedia.org/wiki/Analog_electronics "Any change in the signal is meaningful, and each level of the signal represents a different level of the phenomenon that it represents." This isn't the case with the output from a charge amplifier. 0.050,000 volts represents 50,000 electrons. 0.050,000,4 volts still represents 50,000 electrons. But 0.050,001 volts represents 50,001 electrons as does 0.050,000,6 volts. In summary: --- Analogue electronics (or analog in American English) are those electronic systems with a continuously variable signal. In contrast, in digital electronics signals usually take only two different levels. The term "analogue" describes the proportional relationship between a signal and a voltage or current that represented the signal. " ... _usually_ take only two different levels." But what about Rambus XDR memory which uses three different levels? Two levels are used because they are the simplest. In the case of an image sensor, the output voltage is an analog to the light level that impinges upon it. It still has to be capable of accurate digitisation and to that extent it is digital. Eric Stevens |
#52
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Could you actually see photos made from RAW files?
Eric Stevens wrote:
On Wed, 03 Jun 2009 11:37:23 +1000, Bob Larter wrote: Eric Stevens wrote: Are you really saying that a given RAW data file can be created by more than one image? Yes. If you think carefully about how an image sensor works, it's obvious. I may be missing something but its not obvious to me. A lens directs light from a scene so as to form an image on the camera's sensor. Different parts of the image fall on individual sensels which, in the time allowed to them, capture photons which generate electrons. The accumulated electrons form an electrical charge in each sensel. Is there any reason to believe that the same scene would necessarily produce the same effect on the sensor every time? In fact, the light is not represented by a steady, consistent flow of photons. The photons arrive at irregular intervals. It's called "photon noise". The effect is that if the same image is projected onto a sensor, each time the sensor is read the image will be recorded with unique data that is not identical to the other times that image is recorded. According to the type of sensel, the charge is 'read' in one way or another, and the quantity of charge converted to digital data. Whoops, you just skipped over an awful lot of very fancy technology. The data from the sensor is analog data. The process by which it is converted to digital data is a one way process that cannot be reversed with accuracy. I've gone into detail on that in another article previously and will not repeat it at length here. The digital value of the charge is saved in an array which enables the value of the charge for each individual sensel to be mapped to the position of the sensel. So it is true that the position is relevant. Leaving out the question of whether or not the data is further massaged by the camera before-hand, the data array is saved as the RAW data file for the image. Okay. That original image on the sensor is characterised by by the raw data array. Any change in the image gives rise to a different data array. Not necessarily. How significant the change is is what determines whether it changes the raw data. Some changes simply are not great enough to cause any difference in the data set. As far as I can see only the one image can give rise to a particular data array. Clearly that is not true. I would be grateful for an explanation of how a different image can give rise to the same data array. You've been given several. -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
#53
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Could you actually see photos made from RAW files?
Chris H wrote:
In message , Floyd L. Davidson writes Everything is either one or the other and nothing can be both.) This is not correct. There are plenty of mixed devices about. Analog Devices make a few of them. You can have a complex device that has, for example, an input that is one and an output that is another. But you cannot have a signal that is both. "Everything" means an atomic device, not a complex device. (My apologies, I wrote the above expecting common sense readers who understood the context.) That is *not* part of the firmware. Firmware, other than setting the ISO gain, has no part in any of that other than turning it on and off. You are referring to 'firmware' as though it was 'hardware'. Yet Nikon can program the camera to behave differently so some software/firmware must be involved. Perfectly correct. That does not cause hardware to become firmware. I am referring to that as hardware because in fact it is hardware. It is not done with software/firmware. Yes it is. What is more I can supply the tools to write the firmware. So you think the analog amplifiers and the ADC are firmware and can be done with software tools??? That's a bit of abject ignorance. It's done with hardware. (I can't tell you which but We have supplied software/firmware tools to more than one OEM digital camera company (P&S variety) Not for those functions you haven't. -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
#54
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Could you actually see photos made from RAW files?
Eric Stevens wrote:
It can be OK for you to do that if you indicate that that is what you have done. But you don't do that. You just delete blocks of text. This can result in me appearing to say something other than what I actually said. It can also result in the deletion of the explanation and justification of what I did say. It doesn't. What you said remains in the original post for all to read. I quote just enough to refresh a reader's memory on what it was. That has *always* been the standard practice on Usenet, though in recent years there have been many many fools who cannot understand how to write concisely nor accurately. But your lack of ability to do so is not a cause for me to take on the same poor style that you use! You can't claim that you don't know any better than this if only for the twenty years of experience you have had with Usenet. What you have been doing would not have been tolerated for one second twenty years ago (yeah - I was there too). Can I assume you didn't have a clue then either? See http://www.softdevlabs.com/personal/Usenet101.html "Please remember that when you do snip portions of a person's post, it's extremely important that you not only indicate that you've done so, but also where you've done so. [5] The commonly accepted way to indicate snips is to simply insert the string "snip" (or similar notation) on a line by itself at the spot where the deleted text used to be. " You saw it on the Internet, so it must be true. Sheesh. Cite an authoritative source. (Actually, I'll challenge you to find anything at all from 20 years ago that says anything like that.) Okay, you don't know what an analog device is, so lets go over that too. The definition of "analog" is that the signal (in this case it would be the output signal from the sensor) is continuously variable (it has an infinite number of possible values). If it is "digital" then it must have a finite set of discrete values. (Note that the two definitions are together all inclusive and are mutually exclusive. Everything is either one or the other and nothing can be both.) Haw. You are now claiming that it is possible to have a continuously variable number of electrons. I maintain the number of electrons can only be represented by integers. So what? That makes the number of electrons digital. But we aren't actually measuring the number of electrons, are we? We are measuring the current that flows as a result of the charge that was stored (which is roughly proportional to the number of electrons). The current that flows is affected not only by the number of electrons, but how fast they move and which direction they go. Both of those characteristics are continuously variable. And hence electric current is analog, and so is voltage. Now, you may notice that the output of the sensor is a voltage which is continuously variable over an infinite number of values between 0 and 1 volts. That makes it an *analog* device by definition. The output of the sensor is an electrical charge. Actually it is a current flowing into the input impedance of an amplifier, and thus producing a voltage. The amplifier is affected by the voltage, which is an analog parameter. The electrical charge is dumped into a charge amplifier and it is this which outputs the voltage. This is the first step in transforming sensor image into the RAW data file. And it is clearly an all analog process. That analog data is fed into a device that converts it to digital data. The output of the charge amplifier is then digitised. This is the Actually it is a voltage amplifier. second step in transforming sensor image into the RAW data file. Well, actually it is then run through ISO amplifiers, but we could ignore those is you like. The output has a finite set of discrete values. If, for example, it is a 12-bit digital signal then there are as many as 4096 values. In the case of the Nikon D300 the RAW file can be output as either 12 bit or 14 bit. It is likely that before it can be transformed into either of those formats it is processed in the camera in some other format. Why is that likely? That is what the output of the ADC is, and all that necessarily happens after that is the data stream is read by the CPU so that it can be written to the file. These values are not continuous (i.e., 3 and 4 are discrete and there are no values between them as there would be for an analog signal), hence they are discrete, and the signal is by definition *digital*. Before it hits the RAW file, the data is further massaged. For several paragraphs now your comments have had absolutely nothing to do with the text you are quoting. What's your point? The reason I've been stating that there are many possible images which can produce the same digital data set is because the analog signal to produce any single one of those 4096 values has an infinite number of possible values. Not so. Claim that all you like, but it is true. The digital value of say 1612 corresponds with only one state of the particular sensor element. False. It corresponds to a range of values. Because the range is analog, there are an infinite number of possible values in that range. After the data is digitized, it has one value (1612) and you cannot determine which of the infinite number of analog values that could be 1612 it actually was to start with. If you know the chain of transformations between the sensels and the corresponding data of the RAW file you can work it backwards to derive from the RAW file the state of the individual sensels which gave rise to the data in the first place. False. The reason I've said you cannot precisely restore the original image on the sensor is because you do not know exactly which of the infinite number of possible values for each digital value should actually be used for the analog image. But you do if you understand the nature of the transformation. No, if you understand the nature of the transform then you realize that exactly the opposite is true. The digital value of 1612 might, for example, represent a range of voltages between .25 and .30 volts. When you look at the digital value of 1612, you cannot determine if it was .26675382, or .28778391. All you know that is was between .25 and .30 volts. Basic information theory. (Ever heard of Claude E. Shannon??) Of course I have. What exactly does he have to do with it? Everything. He more or less defined all of it with mathematics, and analyzed what it meant. Because of his work it was decided that the telecommunications industry would benefit from moving to a digital network and abandon the analog network. It was also clear that digital imaging would be much much preferred to analog imaging. That is why inventions which appeared to be useful for digital photography were developed instead of ignored, even though there was no market at all for them at the time. I am referring to that as hardware because in fact it is hardware. It is not done with software/firmware. This is much like the way you insisted for article after article that the RAW data had been interpolated... You had led me onto the garden path for that one. You are the one who takes these hikes into fantasy land Eric, not me. We are discussing a topic that I've been working with for literally decades, and one that I'm familiar with down to the bit diddling level. I may not always be able to describe things in a way that every given individual can understand clearly, but with help from the individual I can eventually find it. The problem here is that while I clearly do understand all of this extremely well and you don't, you won't help with learning it. Nevertheless there is software between the formation of the image on the sensor and the writing of the data to the RAW file. But that software is *not* image manipulation software. All it necessarily does is encode the data so that it can be written to a standard file format. That is why/how various problems (e.g. vertical stripes) can be cured by a firmware upgrade. That sounds more like the image manipulation that is done to the JPEG conversion, not to raw data. Regardless, it would also be possible to introduce banding by dropping data bits or whatever as the data is encoded for writing to a file. That is *not* image manipulation software, and correcting it with a firmware upgrade does not support your arguments. The original argument was over whether or not it was possible to work back from the RAW data and arrive at more than one sensor image. I A nonsense idea, but... Its not at all nonsense, even if you think it is so. Except for one little problem: you can't do it. (That, as I and everyone except you seems to realize, makes it nonsense.) See http://www.clarkvision.com/imagedeta...mance.summary/ for a better indication of the number of electrons you can expect to deal with: 50,000 or more. The little guy standing there looking into the well and counting those electrons might be digital, eh? But since what cameras do is discharge the device through an impedance and amplify the voltage, we don't have a digital count of electrons, we have an analog signal indicating how much charge there was. Of course it includes noise, so even if we did know the exact analog voltage (which as has been show, we cannot), we still wouldn't be able to determine how many electrons were actually captured. Unless you happen to know that digital guy there counting them, and he doesn't run away because of your tin foil hat. Or some other nonsense... article. It isn't rocket science. But it *is* something I've been dealing with for 40 years now... and hence it is not at all surprising that I might understand it rather well and can explain it in 15 different ways. But it does make all of your petty insults a bit of a joke, Eric. Congratulations! 40 years ago you were working in Bell Labs along with Boyle and Smith! And I thought you were only a psychologist. Well, I didn't ever work at Bell Labs, but in fact I did work for AT&T. The telecommunications industry of course has been vitally interested in exactly this business of digital vs analog data roughly since the 1930's in this context. -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
#55
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Could you actually see photos made from RAW files?
Eric Stevens wrote:
On Wed, 03 Jun 2009 11:51:59 +1000, Bob Larter wrote: Eric Stevens wrote: On Tue, 02 Jun 2009 02:09:19 -0800, (Floyd L. Davidson) wrote: [...] The definition of "analog" is that the signal (in this case it would be the output signal from the sensor) is continuously variable (it has an infinite number of possible values). If it is "digital" then it must have a finite set of discrete values. (Note that the two definitions are together all inclusive and are mutually exclusive. Everything is either one or the other and nothing can be both.) Haw. You are now claiming that it is possible to have a continuously variable number of electrons. I maintain the number of electrons can only be represented by integers. By that exact same logic, resistors capacitors & transistors should be called "digital" devices, but they aren't. The industry definition of "digital" is something that only works with binary levels. Everything else is called "analog". References: http://en.wikipedia.org/wiki/Digital_electronics "In a digital circuit, a signal is represented in discrete states or logic levels." - but they don't have to be binary. What's your point? Binary is necessarily digital, but digital is not necessarily binary (though any value that is digital can necessarily be encoded in a binary form). Got that? The point is still that while the number electrons on the head of a pin might be discrete, the current produces by the flow of those electrons is *not* discrete, and therefore is analog. Of course the output of an electronic sensor in a camera is the analog current, not the discrete number of electons capture. http://en.wikipedia.org/wiki/Analog_electronics "Any change in the signal is meaningful, and each level of the signal represents a different level of the phenomenon that it represents." That is correct. Any change is meaningful on the *input* to whereever the signal goes. It does *not* necessarily mean it somehow is meaningful to anything else (such as the number of electrons that cause the signal to exist). This isn't the case with the output from a charge amplifier. 0.050,000 volts represents 50,000 electrons. 0.050,000,4 volts still represents 50,000 electrons. But 0.050,001 volts represents 50,001 electrons as does 0.050,000,6 volts. Is that supposed to make sense? The output from the amplifier is an analog signal. Anything you thing means otherwise is nonsense. If you doubt that, explain how and why it is fed to an analog amplifier and then to a device called an Analog-to-Digital-Converter. In summary: --- Analogue electronics (or analog in American English) are those electronic systems with a continuously variable signal. In contrast, in digital electronics signals usually take only two different levels. The That isn't really true, about "signals usually take only two ...". In fact the entire digital Public Switched Telephone Network (PSTN), as well as virtually all of the music and video that is digitally recorded, uses what is called an m-ary level encoding. In most cases that is a 255 level PCM digital signal. term "analogue" describes the proportional relationship between a signal and a voltage or current that represented the signal. " ... _usually_ take only two different levels." But what about Rambus XDR memory which uses three different levels? Two levels are used because they are the simplest. In the case of an image sensor, the output voltage is an analog to the light level that impinges upon it. It still has to be capable of accurate digitisation and to that extent it is digital. That statement is pure nonsense. It doesn't "have to be capable of accurate digitisation", whatever it is that you think that means. It is not digital in any way until it *is* digitized. -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
#56
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Could you actually see photos made from RAW files?
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#57
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Could you actually see photos made from RAW files?
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#59
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Could you actually see photos made from RAW files?
On Tue, 02 Jun 2009 23:00:27 -0800, (Floyd L.
Davidson) wrote: Eric Stevens wrote: It can be OK for you to do that if you indicate that that is what you have done. But you don't do that. You just delete blocks of text. This can result in me appearing to say something other than what I actually said. It can also result in the deletion of the explanation and justification of what I did say. It doesn't. What you said remains in the original post for all to read. I quote just enough to refresh a reader's memory on what it was. That has *always* been the standard practice on Usenet, though in recent years there have been many many fools who cannot understand how to write concisely nor accurately. But your lack of ability to do so is not a cause for me to take on the same poor style that you use! You can't claim that you don't know any better than this if only for the twenty years of experience you have had with Usenet. What you have been doing would not have been tolerated for one second twenty years ago (yeah - I was there too). Can I assume you didn't have a clue then either? See http://www.softdevlabs.com/personal/Usenet101.html "Please remember that when you do snip portions of a person's post, it's extremely important that you not only indicate that you've done so, but also where you've done so. [5] The commonly accepted way to indicate snips is to simply insert the string "snip" (or similar notation) on a line by itself at the spot where the deleted text used to be. " You saw it on the Internet, so it must be true. Sheesh. Cite an authoritative source. (Actually, I'll challenge you to find anything at all from 20 years ago that says anything like that.) I mightn't find the rules but I can find plenty of examples where that was what was done. Okay, you don't know what an analog device is, so lets go over that too. The definition of "analog" is that the signal (in this case it would be the output signal from the sensor) is continuously variable (it has an infinite number of possible values). If it is "digital" then it must have a finite set of discrete values. (Note that the two definitions are together all inclusive and are mutually exclusive. Everything is either one or the other and nothing can be both.) Haw. You are now claiming that it is possible to have a continuously variable number of electrons. I maintain the number of electrons can only be represented by integers. So what? That makes the number of electrons digital. Can I quote that to the Floyd L. Davidson with whom I've just been arguing? But we aren't actually measuring the number of electrons, are we? We are measuring the current that flows as a result of the charge that was stored (which is roughly proportional to the number of electrons). The current that flows is affected not only by the number of electrons, but how fast they move and which direction they go. Both of those characteristics are continuously variable. Thats why the actual measurement is of charge 'q'. And hence electric current is analog, and so is voltage. And you are the guy who has just explained that 255 levels of current or voltage can be used to carry tone signals. But no, that's not digital or digitized. :-( Now, you may notice that the output of the sensor is a voltage which is continuously variable over an infinite number of values between 0 and 1 volts. That makes it an *analog* device by definition. The output of the sensor is an electrical charge. Actually it is a current flowing into the input impedance of an amplifier, and thus producing a voltage. That's how the electrical charge is measured. The amplifier is affected by the voltage, which is an analog parameter. If you measure it with sufficient precision you can use it to carry digital data. The electrical charge is dumped into a charge amplifier and it is this which outputs the voltage. This is the first step in transforming sensor image into the RAW data file. And it is clearly an all analog process. That analog data is fed into a device that converts it to digital data. The output of the charge amplifier is then digitised. This is the Actually it is a voltage amplifier. Ew've done that bit already. second step in transforming sensor image into the RAW data file. Well, actually it is then run through ISO amplifiers, but we could ignore those is you like. The output has a finite set of discrete values. If, for example, it is a 12-bit digital signal then there are as many as 4096 values. In the case of the Nikon D300 the RAW file can be output as either 12 bit or 14 bit. It is likely that before it can be transformed into either of those formats it is processed in the camera in some other format. Why is that likely? That is what the output of the ADC is, and all that necessarily happens after that is the data stream is read by the CPU so that it can be written to the file. But in what form is it whenit is read by the CPU - 12 bit or 14 bit or something else again? These values are not continuous (i.e., 3 and 4 are discrete and there are no values between them as there would be for an analog signal), hence they are discrete, and the signal is by definition *digital*. Before it hits the RAW file, the data is further massaged. For several paragraphs now your comments have had absolutely nothing to do with the text you are quoting. What's your point? I'm beginning to think you really don't know anything about the logic of any of these processes. The reason I've been stating that there are many possible images which can produce the same digital data set is because the analog signal to produce any single one of those 4096 values has an infinite number of possible values. Not so. Claim that all you like, but it is true. The digital value of say 1612 corresponds with only one state of the particular sensor element. False. It corresponds to a range of values. Because the range is analog, there are an infinite number of possible values in that range. Analog electronic charge. Haw! After the data is digitized, it has one value (1612) and you cannot determine which of the infinite number of analog values that could be 1612 it actually was to start with. You might be correct if they truly were analog, but they aren't. If you know the chain of transformations between the sensels and the corresponding data of the RAW file you can work it backwards to derive from the RAW file the state of the individual sensels which gave rise to the data in the first place. False. So you keep saying. The reason I've said you cannot precisely restore the original image on the sensor is because you do not know exactly which of the infinite number of possible values for each digital value should actually be used for the analog image. But you do if you understand the nature of the transformation. No, if you understand the nature of the transform then you realize that exactly the opposite is true. The digital value of 1612 might, for example, represent a range of voltages between .25 and .30 volts. When you look at the digital value of 1612, you cannot determine if it was .26675382, or .28778391. All you know that is was between .25 and .30 volts. I think the design of sensels has progressed since you helped invent them. Their charge can be read with much greater precision than you seem to think. Basic information theory. (Ever heard of Claude E. Shannon??) Of course I have. What exactly does he have to do with it? Everything. He more or less defined all of it with mathematics, and analyzed what it meant. Because of his work it was decided that the telecommunications industry would benefit from moving to a digital network and abandon the analog network. It was also clear that digital imaging would be much much preferred to analog imaging. That is why inventions which appeared to be useful for digital photography were developed instead of ignored, even though there was no market at all for them at the time. I know all that. But what does he have to do with this particular argument? I am referring to that as hardware because in fact it is hardware. It is not done with software/firmware. This is much like the way you insisted for article after article that the RAW data had been interpolated... You had led me onto the garden path for that one. You are the one who takes these hikes into fantasy land Eric, not me. We are discussing a topic that I've been working with for literally decades, and one that I'm familiar with down to the bit diddling level. I may not always be able to describe things in a way that every given individual can understand clearly, but with help from the individual I can eventually find it. The problem here is that while I clearly do understand all of this extremely well and you don't, you won't help with learning it. It takes two to cooperate. Apart from that, I think we are approaching this from two different directions. My background includes university training in physics, electronics and mathematics. My terminology is different from yours (e.g. transform) and so to is my approach to the problem. Nevertheless there is software between the formation of the image on the sensor and the writing of the data to the RAW file. But that software is *not* image manipulation software. All it necessarily does is encode the data so that it can be written to a standard file format. In the case of the D300 I do not think that is the case. That is why/how various problems (e.g. vertical stripes) can be cured by a firmware upgrade. That sounds more like the image manipulation that is done to the JPEG conversion, not to raw data. I'm talking of raw data. Then Nikons apply a characterisation curve to the senso data before it is recorded as RAW file data. There is much more. Regardless, it would also be possible to introduce banding by dropping data bits or whatever as the data is encoded for writing to a file. That is *not* image manipulation software, and correcting it with a firmware upgrade does not support your arguments. The original argument was over whether or not it was possible to work back from the RAW data and arrive at more than one sensor image. I A nonsense idea, but... Its not at all nonsense, even if you think it is so. Except for one little problem: you can't do it. (That, as I and everyone except you seems to realize, makes it nonsense.) I don't have the information but I am sure the process is reversible (Subject to statistical error limitations). See http://www.clarkvision.com/imagedeta...mance.summary/ for a better indication of the number of electrons you can expect to deal with: 50,000 or more. The little guy standing there looking into the well and counting those electrons might be digital, eh? In his own way, he is. But since what cameras do is discharge the device through an impedance and amplify the voltage, we don't have a digital count of electrons, we have an analog signal indicating how much charge there was. Of course it includes noise, so even if we did know the exact analog voltage (which as has been show, we cannot), we still wouldn't be able to determine how many electrons were actually captured. How do you think you get a digital display to X significant figures on a digital volt meter? Thats the same way that the output of a charge amplifier is digitised. Unless you happen to know that digital guy there counting them, and he doesn't run away because of your tin foil hat. Or some other nonsense... article. It isn't rocket science. But it *is* something I've been dealing with for 40 years now... and hence it is not at all surprising that I might understand it rather well and can explain it in 15 different ways. But it does make all of your petty insults a bit of a joke, Eric. Congratulations! 40 years ago you were working in Bell Labs along with Boyle and Smith! And I thought you were only a psychologist. Well, I didn't ever work at Bell Labs, but in fact I did work for AT&T. The telecommunications industry of course has been vitally interested in exactly this business of digital vs analog data roughly since the 1930's in this context. Boyle and Smith were the inventors of electronic imaging 40 years ago. If you were working with electronic imaging 40 years ago you _must_ have been working with Boyle and Smith. Eric Stevens |
#60
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Could you actually see photos made from RAW files?
Bob Larter was inspired to say
Eric Stevens wrote: On Mon, 01 Jun 2009 06:12:17 -0400, nospam wrote: In article , Eric Stevens wrote: [..] I've quoted from the original articls, and you still keep trying to switch to conversion from RAW to JPG. That's an entirely different question. Then stop talking about processing the RAW data to make an image. I haven't been. If anything I've been talking about working backwards from the RAW data file to reconstruct the original image. that doesn't make any sense. I'm talking in the hypothetical sense of being able to derive from the RAW data the light pattern which fell on the sensor to create the RAW data in the first place. In the case of RAW data which has not been messed around in some way there is only the one sensor image which will correspond. That's incorrect. In a Bayer pattern image sensor, for example, fully half of the sensels can't 'see' red or blue light. As a theoretical example, imagine if you projected a series of images onto the sensor, patterned such that the only difference was in the amounts of red/blue light on the green-sensitive sensels, you would get a series of identical RAW files. This is obviously a very contrived example, but it demonstrates the possibility. ISTM to be relevant to point out that even if no processing of the data is required (it is, of course if only to label the format and cell layout) - the distribution of colour sensors are different from a tft screen and so the RAW 'image' cannot be viewed without interpretation. I'll go back to sleep now... Mike -- "I never have taken a picture I've intended. They're always better or worse." Diane Arbus |
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