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#21
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Could you actually see photos made from RAW files?
In article , Bob Larter
wrote: TTBOMK, the only transformation is the A2D conversion. And that lack of transformations is, after all, the whole point of the RAW file format in the first place. basically that's true, however, nikon did apply white balance to the raw data in some cameras before writing it to the file (d1 series, if i recall). i doubt that's what he meant, and as far as i know, it's no longer done. God, I'd hope not! There are two reasons why I shoot RAW: (1) to get the most dynamic range from my shots, ie; to push them a stop or two, & (2) To fix the white balance for shots that were taken under mixed lighting. turns out it was the d2x. http://imaging.nikon.com/products/im...ne/10/index_02. htm Conventionally, white balance is conditioned digitally. Once an image is taken with a digital camera, A/D conversion occurs first, then this digital image is evaluated to determine the white balance value, according to the conventional process. With the D2X, however, the white balance adjustment is in analog, which means that white balance value is determined for the image before A/D conversion. So we had to figure out a new mechanism for this. i don't think it's inherently bad, especially if it does produce better results, but i do agree that raw should be raw. not to sidetrack, but the only cameras that actually do a transform are sigma/foveon. the raw data in a sigma raw file is *not* what came off the sensor and has gone through quite a bit of processing before being written to the file (which is kinda funny, given the crazy claims about it being 'true colour'). Yuck. IMHO, the whole point of RAW images is that they haven't been screwed around with. the cameras have a 12 bit a/d converter so the raw values should be 0-4095. instead, they range from negative numbers to around 10,000. i don't know why they did that, since the original sd9/10 only outputted raw and you *had* to process it (again) on the computer. what's ironic is the sigma fanbois brag about true colour, the purity of the data, how nothing is interpolated and how perfect the results are. it turns out there's actually *more* going on than with bayer. |
#22
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Could you actually see photos made from RAW files?
On Mon, 01 Jun 2009 06:12:17 -0400, nospam
wrote: In article , Eric Stevens wrote: The "RAW data file" is merely a file containing the camera raw data. The only part of the file that relates to the image is the data it contains. Which is to say that we *are* talking about the "RAW data", even if you want to call if a "RAW data file". It's the same data either way. Nope. What comes out of the sensor is not what is saved in the RAW file. There is a transformation involved. what type of transformation and from what to what? There is no single answer. It depends on the camera and the manufacturer. I suppose there are cameras which save a RAW file which is nothing but a bit-map of the sensor but generally the RAW file is modified in some way. In the case of the Nikon D300 there are several choices as to how the RAW file may be saved: Compressed, lossless compression or lossy compression. 12 bit or 14 bit. I don't know the details of this but I expect that some of it is described in the Nikon Software Developers Kit. Whatever it is that happens, clearly there is a transformation of some kind. It is interesting that the D300 manual specifically says of the lossy compression: "NEF images are compressed using a non-reversible algorithm, reducing the file size by about 40-55% with almost no effect on image quality" This contradicts what I was saying to Floyd: it is not possible to go back to the original sensor image from the RAW file. There will be a range of slightly different sensor images which could produce the same RAW file. depending on the camera, there may be minor changes such as analog white balance or noise reduction, but for all intents the data in the raw file *is* the data off the sensor, at least with bayer sensors. Note that "sensor data", in the context of this discussion, would be the analog data directly read from the sensor .... ... what analog data? from the sensor, before the a/d converter. Second, in the case of the Nikon D300 the update has changed the way in which the raw data from the sensors have been interpreted and saved to the RAW file. Nice try, but I just read the release notes for Nikon's upgraded firmware for the D300, and saw exactly *nothing* like what you are saying. Provide details, and be specific. What do you make of: . Image quality: NEF (RAW ) + JPEG . NEF (RAW) recording: Lossless compressed or Compressed . Image size: S or M That sounds like a change in the way raw data from the sensors have been interpreted and saved to the RAW file. no it doesn't. the first is embedding the jpeg in addition to the raw data and the second is how it's compressed. the third is for the size of the jpeg file. raw files are always full size, with canon's sraw being an exception (and since this is a nikon d300, not applicable). See above. The RAW data can be compressed independently of the JPEG compression. I wouldn't argue with you over what you have just said but I would like to point out that this discussion has been about the interpolated data saved in the RAW file. The raw data saved in the RAW file is not interpolated. See the last line of ... http://en.wikipedia.org/wiki/Bayer_filter "Bryce Bayer's patent called the green photosensors luminance-sensitive elements and the red and blue ones chrominance-sensitive elements. He used twice as many green elements as red or blue to mimic the human eye's greater resolving power with green light. These elements are referred to as sensor elements, sensels, pixel sensors, or simply pixels; sample values sensed by them, after interpolation, become image pixels." Didn't you read what that paragraph says???? Are you unable to determine that the "after interpolation" is refering not to generation of data that goes into the RAW file, but rather what is done with data *from* the RAW file in order to make an image (such as TIFF or JPEG). That is what "image pixels" means. Haw! You really don't understand what Bayer interpolation is all about. if anyone doesn't understand it, it's you. nowhere in what *you* quoted says the data in the raw *file* is interpolated. I've got to plead guilty to that. In a moment of brain fade I got sucked into what Floyd was trying to talk about rather than the original topic which I was trying to talk about. Rereading all this below I can see that I had become more than somewhat confused. the interpolation is done in the raw converter on the computer, long after the raw file has been created. The data saved in the RAW file has not yet been interpolated, .... How else do you reckon it is derived from the Bayer mosaic? the data in the raw file is *before* the interpolation is done to demosaic the image. ... and when it is interpolated it is *not* saved in the RAW file, and is no longer considered "raw" data. Well, at least you understand that much. odd, because that contradicts what you've been saying. However, in addition to that the JPEG image which results from interpolation simply does not contain anything like the full amount of information that was in the RAW file's data. You cannot reverse the process. HOW DO I MAKE IT CLEAR THAT FROM THE BEGINNING WE HAVE BEEN TALKING ABOUT THE RELATIONSHIP BETWEEN THE ORIGINAL IMAGE ON THE SENSOR AND THE 'RAW' FILE. Then don't talk about interpolation and other software processing of the raw data, all of which takes place on data *after* it is placed in the RAW file. Dingbat - interpolation is an assential part of going from the Bayer array to the RAW data file. Please don't continue to pretend otherwise. no need to pretend otherwise since that's totally incorrect. 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. Eric Stevens |
#23
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Could you actually see photos made from RAW files?
In article , Eric Stevens
wrote: The "RAW data file" is merely a file containing the camera raw data. The only part of the file that relates to the image is the data it contains. Which is to say that we *are* talking about the "RAW data", even if you want to call if a "RAW data file". It's the same data either way. Nope. What comes out of the sensor is not what is saved in the RAW file. There is a transformation involved. what type of transformation and from what to what? There is no single answer. that's ok, just one example is fine. It depends on the camera and the manufacturer. I suppose there are cameras which save a RAW file which is nothing but a bit-map of the sensor actually, just about every camera. but generally the RAW file is modified in some way. nothing that would affect bayer interpolation. there may be some noise reduction or in the case of the nikon d2x, white balance. In the case of the Nikon D300 there are several choices as to how the RAW file may be saved: Compressed, lossless compression or lossy compression. compression is not modification. it's there to save space. users like being able to put more photos on a card so smaller raw files is a plus. now, the lossless compression is a modification, although nikon claims it's 'visually lossless.' it's also optional and it's a tradeoff for an even smaller size image. 12 bit or 14 bit. that's not a modification, that's choosing the resolution of the a/d converter. I don't know the details of this but I expect that some of it is described in the Nikon Software Developers Kit. Whatever it is that happens, clearly there is a transformation of some kind. if it's so clear, where's the evidence? It is interesting that the D300 manual specifically says of the lossy compression: "NEF images are compressed using a non-reversible algorithm, reducing the file size by about 40-55% with almost no effect on image quality" This contradicts what I was saying to Floyd: it is not possible to go back to the original sensor image from the RAW file. There will be a range of slightly different sensor images which could produce the same RAW file. lossy compressed raw is the only case where you don't have an exact sensor dump (but it's *very* close). fortunately, the d300 offers uncompressed and lossless compressed. That sounds like a change in the way raw data from the sensors have been interpreted and saved to the RAW file. no it doesn't. the first is embedding the jpeg in addition to the raw data and the second is how it's compressed. the third is for the size of the jpeg file. raw files are always full size, with canon's sraw being an exception (and since this is a nikon d300, not applicable). See above. The RAW data can be compressed independently of the JPEG compression. yea and? Haw! You really don't understand what Bayer interpolation is all about. if anyone doesn't understand it, it's you. nowhere in what *you* quoted says the data in the raw *file* is interpolated. I've got to plead guilty to that. In a moment of brain fade I got sucked into what Floyd was trying to talk about rather than the original topic which I was trying to talk about. Rereading all this below I can see that I had become more than somewhat confused. at least you realize you're confused. |
#25
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Could you actually see photos made from RAW files?
On Tue, 02 Jun 2009 02:59:51 +1000, Bob Larter
wrote: Eric Stevens wrote: Nope. What comes out of the sensor is not what is saved in the RAW file. There is a transformation involved. What transformation is that? TTBOMK, the only transformation is the A2D conversion. And that lack of transformations is, after all, the whole point of the RAW file format in the first place. AFAIK the contents of the RAW file (ignoring metadata etc) is a fully detailed map of the sensor data but is not just a 'dump' of the sensor data. At the very least the quantized sensor voltage has to be transformed into 12 or 14 bit data. Various corrections may be applied in the process. Eric Stevens |
#26
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Could you actually see photos made from RAW files?
On Tue, 02 Jun 2009 00:28:02 +1000, Bob Larter
wrote: Eric Stevens wrote: On Sun, 31 May 2009 16:11:00 -0800, (Floyd L. [...] I've been talking about the RAW file from the beginning. So too were you at that time. Remember "Floyd, I suspect you have been smoking something which is not good for you. Subject to statistical error limitations, ... The data in the RAW file can't be restructured to make a different image without changing the data." This is incorrect. As Floyd has said, the same RAW data can result in an infinite number of final images. For example, one can process it with a huge range of WB values, or change the EV correction by plus or minus a couple of stops, set the black level to anything you like, etc, etc. None of these changes require changes to the RAW data, merely the interpretation of it. Its incorrect, as you (or somebody) chopped out the important part. I originally wrote: "Floyd, I suspect you have been smoking something which is not good for you. Subject to statistical error limitations, there is a one to one correspondence between the source image and the RAW file. One can be converted to the other using the rules inherent in the camera's software. The data in the RAW file can't be restructured to make a different image without changing the data." We were then talking about the "source image" - that which was projected onto the sensor by the lens - and not that infinite range of images which could be created downstream by the manipulation of the RAW data. Eric Stevens |
#27
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Could you actually see photos made from RAW files?
On Tue, 02 Jun 2009 00:19:18 +1000, Bob Larter
wrote: Eric Stevens wrote: On Sat, 30 May 2009 21:32:27 -0800, (Floyd L. Davidson) wrote: Floyd has failed to point out that at this point he has omitted a great deal of previous text. I know he has been around more than long enough to know that this is not the right thing to do. Eric Stevens wrote: Floyd, I suspect you have been smoking something which is not good for you. Subject to statistical error limitations, there is a one to one correspondence between the source image and the RAW file. One can be converted to the other using the rules inherent in the camera's software. What do you mean by "the source image"? That which is projected onto the sensor by the lens. That's what's encoded in the RAW file. It's a losslessly compressed dump of the contents of the image sensor, without any interpretation. Not so. The sensor stores volts. The RAW file maps this in 12 or 14 bit patterns. Some transformation has clearly taken place. Nor is it necessarily compressed and, if compression has taken place it need not be lossless. [...] file. You don't have a choice of RAW files for a given image. Nor do you have a choice of images for a given RAW file. Did you read, and understand, the following few paragraphs? A JPEG or TIFF file contains an image. The RAW file contains data to make an image. For example, each "sensal" location on the sensor does *not* translate to a single pixel in the resulting image. Instead the data from at least 9 different sensors locations is used to determine the Red, Green, and Blue values for a single pixel. He's talking about the *process* of converting from the RAW image to the RGB image that you see on your screen, which includes Bayer deconvolution. As he says, there is no 1:1 relationship between a pixel ("sensel") on the image sensor & a pixel on the RGB image that you see on your screen. My original proposition was that there is a one to one correspondence between the source image (that which is projected onto the sensor by the lens) and data which is stored in the RAW file. Its not possible that any single RAW file could be produced by more than one sensor image. Eric Stevens |
#28
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Could you actually see photos made from RAW files?
On Mon, 01 Jun 2009 18:24:28 -0400, nospam
wrote: In article , Eric Stevens wrote: The "RAW data file" is merely a file containing the camera raw data. The only part of the file that relates to the image is the data it contains. Which is to say that we *are* talking about the "RAW data", even if you want to call if a "RAW data file". It's the same data either way. Nope. What comes out of the sensor is not what is saved in the RAW file. There is a transformation involved. what type of transformation and from what to what? There is no single answer. that's ok, just one example is fine. It depends on the camera and the manufacturer. I suppose there are cameras which save a RAW file which is nothing but a bit-map of the sensor actually, just about every camera. but generally the RAW file is modified in some way. nothing that would affect bayer interpolation. there may be some noise reduction or in the case of the nikon d2x, white balance. In the case of the Nikon D300 there are several choices as to how the RAW file may be saved: Compressed, lossless compression or lossy compression. compression is not modification. it's there to save space. users like being able to put more photos on a card so smaller raw files is a plus. now, the lossless compression is a modification, although nikon claims it's 'visually lossless.' it's also optional and it's a tradeoff for an even smaller size image. 12 bit or 14 bit. that's not a modification, that's choosing the resolution of the a/d converter. I don't know the details of this but I expect that some of it is described in the Nikon Software Developers Kit. Whatever it is that happens, clearly there is a transformation of some kind. if it's so clear, where's the evidence? With all these changes to its form, the original data has clearly been transformed. This does not mean that its meaning has been changed. Merely that its form has been changed. It is interesting that the D300 manual specifically says of the lossy compression: "NEF images are compressed using a non-reversible algorithm, reducing the file size by about 40-55% with almost no effect on image quality" This contradicts what I was saying to Floyd: it is not possible to go back to the original sensor image from the RAW file. There will be a range of slightly different sensor images which could produce the same RAW file. lossy compressed raw is the only case where you don't have an exact sensor dump (but it's *very* close). fortunately, the d300 offers uncompressed and lossless compressed. That sounds like a change in the way raw data from the sensors have been interpreted and saved to the RAW file. no it doesn't. the first is embedding the jpeg in addition to the raw data and the second is how it's compressed. the third is for the size of the jpeg file. raw files are always full size, with canon's sraw being an exception (and since this is a nikon d300, not applicable). See above. The RAW data can be compressed independently of the JPEG compression. yea and? Haw! You really don't understand what Bayer interpolation is all about. if anyone doesn't understand it, it's you. nowhere in what *you* quoted says the data in the raw *file* is interpolated. I've got to plead guilty to that. In a moment of brain fade I got sucked into what Floyd was trying to talk about rather than the original topic which I was trying to talk about. Rereading all this below I can see that I had become more than somewhat confused. at least you realize you're confused. Your turn now. Have a look at what I am trying to say about the meaning of transformation. 1/4 = 0.25 Eric Stevens |
#29
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Could you actually see photos made from RAW files?
nospam wrote:
In article , Bob Larter wrote: He's talking about the *process* of converting from the RAW image to the RGB image that you see on your screen, which includes Bayer deconvolution. As he says, there is no 1:1 relationship between a pixel ("sensel") on the image sensor & a pixel on the RGB image that you see on your screen. there is a 1:1 mapping of senselsixels, although multiple sensels are used to calculate one pixel. in other words, 10 million sensels on the sensor- 10 million pixels in the image. Untrue. There are necessarily more sensor locations than pixels in the resulting image. Various different raw converters, all using the same raw data, produce images of different pixel counts. -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
#30
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Could you actually see photos made from RAW files?
nospam wrote:
In article , Bob Larter wrote: He's talking about the *process* of converting from the RAW image to the RGB image that you see on your screen, which includes Bayer deconvolution. As he says, there is no 1:1 relationship between a pixel ("sensel") on the image sensor & a pixel on the RGB image that you see on your screen. there is a 1:1 mapping of senselsixels, although multiple sensels are used to calculate one pixel. in other words, 10 million sensels on the sensor- 10 million pixels in the image. That's the default, but there's no mathematical necessity for the number of output pixels to equal the number of output pixels. i would hope the number of output pixels equals the number of output pixels unless you upscale or downscale, the number of input sensels will be the same as the number of output pixels. That is not true. The Nikon D3, as one example, is specified as having a 12.87 Mega pixel sensor. The images it generates are specified to be 4256x2832, which works out to 12.05 Mega pixels. Dave Coffin's dcraw program generates a 4284x2844 (12.18Mp) image. Note also that the camera can generate an image of 2128x1416, and while I do not know the details of how Nikon implemented that, it is entirely possible (and very likely) that it is not done by scaling the larger image to a smaller one, but by simply using a larger block for interpolation of the raw data. -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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