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02-20-2009, 04:05 PM   #46
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Normal is as normal does

QuoteOriginally posted by Marc Sabatella Quote
So anyhow, Brian, while your basic conclusion is correct, I need to quibble with the terminology. Cameras don't have native resolutions that can be expressed in dpi; that's a meaningless statement. It has a certain number of dots (the "d" in dpi), period. The camera has no idea how inches big (the "i" in dpi) the print is going to be, so there is no way to say it has a "native" dpi. Only when you choose a print size in inches can one calculate dpi. Similarly, the trip from Paris to London does not have has a "native" speed in MPH. It has a distance in miles, period. Only when you actually make the trip and time it can you compute a speed in MPH.
All I know is when I download a RAW file from the K100 it comes into PS at 3008x2000 pixels at 240 dpi (as labeled by the program), that's what PS sends to my printer sees and printed output size and resolution I get. If I change the dpi in PS without resampling, however, it spreads those 6mp across a physically larger piece of paper and that changes the qualitative output of the print. Same pixels, different dpi and different print quality. Since that description is tagged to the image (pixels and dpi) that comes out of the camera in RAW, and if I don't amend it in PS that's what PS outputs and what the printer prints. I have to think that's the "normal" description of the RAW data. I'd be happy to use another term to describe it, if anyone can suggest one,
Brian

02-20-2009, 04:31 PM   #47
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QuoteOriginally posted by Class A Quote
I agree with everything you've written, but whether it is 72dpi or not depends on the monitor (the pixels size of the monitor). Many monitors may approximate 72dpi but I have used 96dpi monitors as well.
Right, that's why I said "about" 72dpi. And of course the actual resolution will depend on your display settings too. Another reason to completely ignore this number.

QuoteQuote:
Some browsers (Firefox with default settings) actually scale images in order to normalize the dpi of the monitor. I don't know whether Firefox reads the dpi of the image or just aims at 72dpi but it will scale images depending on its settings.
I've seen no evidence of Firefox using the dpi setting of the file, although I haven't tried all combinations of options.
02-20-2009, 04:51 PM   #48
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QuoteOriginally posted by FHPhotographer Quote
All I know is when I download a RAW file from the K100 it comes into PS at 3008x2000 pixels at 240 dpi (as labeled by the program)
The program might label it 240dpi, but that's just because the camera needed to stick *some* number into that field. It's meaningless. Changing that number (which is stored in the EXIF info) no more changes the actual resolution of the image than changing incrasing the shutter speed stored in the EXIF will suddenly make your picture sharper.

QuoteQuote:
that's what PS sends to my printer
No, your printer just sends pixels. It may scale the pixels first to fit the print size your selected according to how the printer driver asks to have the pixels scaled (not sure how this actually works), but changing that number in the EXIF will no effect whatsoever on what PS sends to the printer or how the printer prints the image.

QuoteQuote:
If I change the dpi in PS without resampling, however, it spreads those 6mp across a physically larger piece of paper and that changes the qualitative output of the print.
No it doesn't. If you lower the dpi figure, it might tell you it that the size you'd need to print at to get that resolution would be larger, but when you go to print the image, it's still going to to use the size you actually specify, not the number it reported as the size you'd have to print at to get the resolution you typed in. The resolution figure and the calculated print size required to achieve that resolution are completely ignored in printing. Well, I suppose PS is a big enough program that somewhere there might be an option to force it resample the image to achieve the specified resoltuion at the print size it is making, but that's certainly not the normal way any progam would work.

QuoteQuote:
Since that description is tagged to the image (pixels and dpi) that comes out of the camera in RAW, and if I don't amend it in PS that's what PS outputs and what the printer prints. I have to think that's the "normal" description of the RAW data. I'd be happy to use another term to describe it, if anyone can suggest one,
It's just a random number the camera stores because it's got to store *something* at that location in the EXIF. Could just as well be 0, or 1, or 72, or 300, or 65535. Actually, I thought it *was* normally 72 - maybe PS is actually changing it to 240 when it imports your images because it knows that is the native resolution of your printer? Or perhaps because you've specified a default print size that happens to work out to 240dpi? Not sure where that's coming from. But it's not the camera that is putting that particular number there - th camera puts 72 there. And regardless of what the number is stored there, it is definitely not any inherent quality of the image - it's just a number stored for no reason whatsoever other than the fact that there is a space to store a number, so *some* number has to be stored there.
02-20-2009, 06:03 PM   #49
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The K100D Super is an amazing camera and I truly doubt, on the basis of IQ, that many people need better. We may want better, but that's a different issue. As others have pointed out, however, the K20D has significantly more features, including weather sealing and more robust build in general.

But one thing that hasn't been mentioned. The K20D is blacker. And I want the blackest camera I can get.

02-20-2009, 06:25 PM   #50
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Most of what you've written is near pointless because we know all that, it was merely a reply to the OPer asking if he should do a pixel for pixel comparison.
02-20-2009, 06:49 PM   #51
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Satisfying the semantic truth conditions...

QuoteOriginally posted by Marc Sabatella Quote
The program might label it 240dpi, but that's just because the camera needed to stick *some* number into that field. It's meaningless. Changing that number (which is stored in the EXIF info) no more changes the actual resolution of the image than changing incrasing the shutter speed stored in the EXIF will suddenly make your picture sharper.



No, your printer just sends pixels. It may scale the pixels first to fit the print size your selected according to how the printer driver asks to have the pixels scaled (not sure how this actually works), but changing that number in the EXIF will no effect whatsoever on what PS sends to the printer or how the printer prints the image.



No it doesn't. If you lower the dpi figure, it might tell you it that the size you'd need to print at to get that resolution would be larger, but when you go to print the image, it's still going to to use the size you actually specify, not the number it reported as the size you'd have to print at to get the resolution you typed in. The resolution figure and the calculated print size required to achieve that resolution are completely ignored in printing. Well, I suppose PS is a big enough program that somewhere there might be an option to force it resample the image to achieve the specified resoltuion at the print size it is making, but that's certainly not the normal way any progam would work.



It's just a random number the camera stores because it's got to store *something* at that location in the EXIF. Could just as well be 0, or 1, or 72, or 300, or 65535. Actually, I thought it *was* normally 72 - maybe PS is actually changing it to 240 when it imports your images because it knows that is the native resolution of your printer? Or perhaps because you've specified a default print size that happens to work out to 240dpi? Not sure where that's coming from. But it's not the camera that is putting that particular number there - th camera puts 72 there. And regardless of what the number is stored there, it is definitely not any inherent quality of the image - it's just a number stored for no reason whatsoever other than the fact that there is a space to store a number, so *some* number has to be stored there.
Sorry, Marc, I am not persuaded by your arguments. If I state that “the normal RAW data file from a Pentax K100 is represented within any/all applications that can view that data as 240dpi” then that statement functions as knowledge of the statement’s truth conditions, i.e., what the world would be like if the sentence were true. So, if any statement that 240dpi is the normal image were true , then the product of the operative application (Photoshop) that defines that data by the statement “the normal image” acting through the intermediate system (printer) appears to be a representation of an image with 240 dots per inch, the truth conditions of that statement are satisfied. Or so it seems to me,
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02-20-2009, 06:51 PM   #52
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I want to agree

QuoteOriginally posted by rparmar Quote
But one thing that hasn't been mentioned. The K20D is blacker. And I want the blackest camera I can get.
Well now, boyo, I can't say if that's true but I certainly want it to be and will raise a pint in support of your argument,
Brian
02-21-2009, 10:00 AM   #53
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QuoteOriginally posted by FHPhotographer Quote
Sorry, Marc, I am not persuaded by your arguments. If I state that “the normal RAW data file from a Pentax K100 is represented within any/all applications that can view that data as 240dpi”
That's not true. If you look a the file with a program that does not try to alter the data (as Photoshop might on import), you'll see it reported as 72dpi. But anyhow, like I said, so what? What differences does it make what number is recorded in the EXIF to represent the "resolution" of the image in dpi?

How about this; you explain what you think it would mean for a camera to have a native resolution in dpi. Tha is, if you had two cameras, one with a "native resolution" of 72dpi, another with a "native resolution" of 240dpi, but both were 6MP cameras (2000x3000 pixels), how could tell the difference? I think that's what you're getting at.

I'll give you my answer: you can't tell the difference, because there is no difference whatsoever. 2000x3000 pixel is 2000x3000 pixels, period. This is a well-known fact. This whole dpi business is a common point of confusion among newcomers to digital imaging technology, which is why I make a point of trying to help clarify it, because it leads to all sorts of incorrect assumptions (it also relates to the common confusion about what constitutes a 100% crop, FWIW). And in some cases, to people shooting themselves in the foot when trying to print or make comparisons, because they are taking the wrong steps. It really is worth understanding this.


Last edited by Marc Sabatella; 02-21-2009 at 10:09 AM.
02-21-2009, 10:05 AM   #54
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QuoteOriginally posted by Marc Sabatella Quote
I'm not even sure what that statement means. How about this; you explain what you think it would mean for a camera to have a native resolution in dpi. Tha is, if you had two cameras, one with a ative reoslution of 72dpi, another with a native resolution of 240dpi, but both were 6MP cameras (2000x3000 pixels), how could tell the difference?

I'll give you my answer: you can't there is no difference whatsoever. 2000x3000 pixel is 2000x3000 pixels, period.
People keep seeing res, ppi and image size as three different measurements when they are all related, it does seem to confuse folks but I am not sure why.

The ppi figure is of course dependent on the image size and the number of pixels. 72 appears a common default but i think that measures something like an image size of 45x30 inches on a 6mp camera.
02-22-2009, 03:11 PM   #55
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what's in a name, but how...

QuoteOriginally posted by Marc Sabatella Quote
That's not true. If you look a the file with a program that does not try to alter the data (as Photoshop might on import), you'll see it reported as 72dpi. But anyhow, like I said, so what? What differences does it make what number is recorded in the EXIF to represent the "resolution" of the image in dpi?

How about this; you explain what you think it would mean for a camera to have a native resolution in dpi. Tha is, if you had two cameras, one with a "native resolution" of 72dpi, another with a "native resolution" of 240dpi, but both were 6MP cameras (2000x3000 pixels), how could tell the difference? I think that's what you're getting at.

I'll give you my answer: you can't tell the difference, because there is no difference whatsoever. 2000x3000 pixel is 2000x3000 pixels, period. This is a well-known fact. This whole dpi business is a common point of confusion among newcomers to digital imaging technology, which is why I make a point of trying to help clarify it, because it leads to all sorts of incorrect assumptions (it also relates to the common confusion about what constitutes a 100% crop, FWIW). And in some cases, to people shooting themselves in the foot when trying to print or make comparisons, because they are taking the wrong steps. It really is worth understanding this.
Ok, this is in two parts: first, you took an if-then statement (about truth conditions) and only responded to the "if" and not the "then." That aside, I'll drop the whole "dpi" thing from now on; there seems to be an overwhelming body of opinion leaning that way. From this day forward, I shall refer to what comes out of the camera as the furshlugener resolution and what PS sees, uses and prints with as the portzebie resolution.

In any case, nomenclature doesn't matter, it's what the print looks like that counts. But I am curious about what constitutes a "100% crop." Maybe you explained it earlier, but I've lost the thread of the thing, so how does one compare dissimilar resolution images at 100% to make a valid printed and/or on-screen evaluation? If this has been covered, a link to that post would do the trick. Thanks,
Brian
02-22-2009, 03:23 PM   #56
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but it's counter intuitive...

QuoteOriginally posted by Alfisti Quote
People keep seeing res, ppi and image size as three different measurements when they are all related, it does seem to confuse folks but I am not sure why.
Well it confuses folks because it is counter intuitive to look at an image that is indexed with a dpi number that apparently is irrelevant, or an arbitrary place holder, totally useless or critically important depending on the source, the application, the output modality, the capture program ad infinitum.

I used to tell my students that everybody had an opinion and the only differences among them was that some opinions were more informed or reasoned than others. As statements of fact, therefore, all opinions are not equal, but as questions about the nature of a thing and its fact base, every opinion is valuable.

Yes, that is a criticism, but I'll let you figure out of what and why,
Brian
02-22-2009, 03:40 PM   #57
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QuoteOriginally posted by FHPhotographer Quote
I used to tell my students that everybody had an opinion and the only differences among them was that some opinions were more informed or reasoned than others. As statements of fact, therefore, all opinions are not equal, but as questions about the nature of a thing and its fact base, every opinion is valuable.
OT but what did you used to teach?
02-22-2009, 03:46 PM   #58
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QuoteOriginally posted by FHPhotographer Quote
Ok, this is in two parts: first, you took an if-then statement (about truth conditions) and only responded to the "if" and not the "then."
True. I did that because it appeared you were trying to make a semantic argument about what to *call* this 240 number, when my whole point was, that 240 number is meaningless - so the rest of your post made no sense to me. I didn't know how to respond, so I didn't.

QuoteQuote:
From this day forward, I shall refer to what comes out of the camera as the furshlugener resolution and what PS sees, uses and prints with as the portzebie resolution.
If "furshlugener" and "portzebie" are words that mean "completely meaningless", then go for it. As long as you persist in assuming there is *any* significance whatsoever to the number 240 in this context, though, you are going to be confused. The number is as irrelevant as the serial number of your camera that is also recorded in the EXIF. The numbers are there, and Photoshop or another program can report them to you, but they *mean* nothing. Changing them doesn't change a thing about the image.

QuoteQuote:
In any case, nomenclature doesn't matter, it's what the print looks like that counts.
True, but if you don't these issues, you can easily end up making invalid comparisons, such as by not realizing when you are throwing away pixels and when you are not. That's how the issue came up, and it remains relevant.

QuoteQuote:
But I am curious about what constitutes a "100% crop."
Its a crop done without resizing. Doesn't matter how big the cropped out area is, as long as you don't resize the image before or after cropping.

QuoteQuote:
Maybe you explained it earlier, but I've lost the thread of the thing, so how does one compare dissimilar resolution images at 100% to make a valid printed and/or on-screen evaluation? If this has been covered, a link to that post would do the trick.
Again, the answer depends on whether your goal is to nullify away the resolution advantage of the K20D or not (for instance, if you just wanted to compare color or contrast). If that is your goal, you wouldn't compare 100% crops at all - you'd resize the K20D image to 2000x3000 first (thus throwing away the extra pixels) before comparing. If you want to see the resolution advantage of the K20D, you make 100% crops from both cameras. For instance, take a portrait with each camera, and cut out just the eye and nose. The K20D has more pixels, so you'll be cutting out a larger area measured in pixels. Meaning, when you display it on screen, it will *look* larger. And you should be able to see more detail.

Last edited by Marc Sabatella; 02-22-2009 at 03:58 PM.
02-22-2009, 03:50 PM   #59
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I really do not understand how this number 72 (or 96) could have any meaning at all. Dpi has nothing to do with monitors.

QuoteQuote:
I agree with everything you've written, but whether it is 72dpi or not depends on the monitor (the pixels size of the monitor). Many monitors may approximate 72dpi but I have used 96dpi monitors as well.
02-22-2009, 04:16 PM   #60
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QuoteOriginally posted by Andreas Quote
I really do not understand how this number 72 (or 96) could have any meaning at all. Dpi has nothing to do with monitors.
DPI does have something to do with monitors. It is the number of actual physical pixels in an inch. If you took a ruler to your monitor, measured an inch, and counted the pixels, that would be your actual DPI value. In practice, 72 (low resolution screens) or 96 (high resolution screens) are the only two values in common usage.

In any case where pixels are mapped onto a physical surface, DPI is a meaningful number. For on-screen data, that means that data displayed on your monitor has a DPI value, but if you took a screengrab, the resulting bitmap would not have a meaningful DPI value. As for photographs or other digital image files, as long as the pixels are only in a digital file, i.e. existing only as data and not on a print, DPI is completely meaningless, because there are no inches to map the dots onto.
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