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02-22-2009, 04:22 PM   #61
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QuoteOriginally posted by FHPhotographer Quote
I'm running some comparisons between my K100D and my new K20. (snip)

Comparing two cameras, using the same settings, is like comparing two pepperoni pizzas, Brian. With the latter, even when both are cooked at the same temperature, same length of times in the same oven, and served on the same tray, there are always going to be some slight differences - especially when prepared and cooked by different chefs, each with different ideas of what makes a good pizza (how much cheese, sauce, pepperoni, each ingredient in the sauce, etc).

With a camera, things like color, saturation, brightness, and others (things similar to those pizza ingredients above), are subjective - a judgement call. Further, those judgements can vary between employees building each camera model and from day to day or month to month even with the same employees. Thus, no two cameras models (made by the same employees or not) are going to be exactly the same. There will always be slight differences. Further, your judgements, which also change constantly, will likely never match those of the manufacturer.

However, all that is exactly why manufacturers build controls into cameras to allow you to make any adjustments you feel are necessary. And that's also why it's not very worthwhile to attempt camera comparisons using only the same settings. If you want a more accurate idea of what each camera can do, it's best to adjust each for their best individual performance and then compare the two at that point to see which camera comes closest to what you actually want.

Of course, that contradicts the long-standing notion of comparing home electronics using the same settings. But, while that method is valid for comparing home stereo speakers without built-in controls (what you hear is what you get), cameras do have considerable built-in controls (which should be used) to adjust their behavior more towards your liking.

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02-22-2009, 06:09 PM   #62
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QuoteOriginally posted by FHPhotographer Quote
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.
An image in memory has no resolution. It only has dimensions (in number of pixels). That is why the viewpoint "the dpi figure in images is meaningless" makes sense.

However, the dpi figure stored in a JPEG can be given a meaning if it is used to instruct, say a printer, to create an output of a particular size (physical dimensions). If you print a 6MP image with 3008 horizontal pixels at 72 dpi, you'll get a 3008/72=41.7 inch wide image. If the dpi figure in the JPEG file says 96, instead of 72, and your software/printer respects the figure, your output imagine will only be 31.3 inch wide.

QuoteOriginally posted by FHPhotographer Quote
But I am curious about what constitutes a "100% crop."
That term refers to a crop of an image where one source pixel is mapped to one output pixel. By looking at the monitor, one monitor pixel will correspond to one source pixel (instead of, e.g., an average value of many source pixels).

QuoteOriginally posted by Erik Quote
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.
It is only meaningless in as much it is interpreted as the resolution of the captured image (which doesn't exist). It has meaning as an instruction for software/printers to achieve a certain image size (and thus a resolution which is expressed in number of pixels per space).


QuoteOriginally posted by stewart_photo Quote
But, while that method is valid for comparing home stereo speakers without built-in controls (what you hear is what you get), cameras do have considerable built-in controls (which should be used) to adjust their behavior more towards your liking.
But one can always show in RAW and use one and the same program for conversion to JPEG, thus eliminating any in-camera conversion differences.
02-22-2009, 06:37 PM   #63
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QuoteOriginally posted by Class A Quote
An image in memory has no resolution. It only has dimensions (in number of pixels). That is why the viewpoint "the dpi figure in images is meaningless" makes sense.

However, the dpi figure stored in a JPEG can be given a meaning if it is used to instruct, say a printer, to create an output of a particular size (physical dimensions). If you print a 6MP image with 3008 horizontal pixels at 72 dpi, you'll get a 3008/72=41.7 inch wide image. If the dpi figure in the JPEG file says 96, instead of 72, and your software/printer respects the figure, your output imagine will only be 31.3 inch wide.
Technically correct, but how often does one consider DPI over print size? When's the last time you said to yourself "I better print this at 240dpi" rather than "I'd like this to be a 12x18 print"?
02-22-2009, 09:48 PM   #64
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QuoteOriginally posted by Alfisti Quote
Isn't the ppi figure and colour space dependent on the way the file was saved?

it doesn't just automatically convert to those settings once you view it ont he web.
I missed this post, sorry. Actually web browsers on computers are only capable of displaying a certain amount of colors, aka sRGB, and only at a certain ppi which is 72 ppi So whenever I output photos for the web, I output it onto sRGB colors instead of relying on the web browsers for conversion, it gives me more control and makes the image sizes smaller

Learned this at all my photography classes that include printing, and the books I have read so far (including the photoshop/photography/lightroom books by Scott Kelby). Hope this helps

02-23-2009, 01:46 AM   #65
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QuoteOriginally posted by Class A Quote
It is only meaningless in as much it is interpreted as the resolution of the captured image (which doesn't exist). It has meaning as an instruction for software/printers to achieve a certain image size (and thus a resolution which is expressed in number of pixels per space).
This is true -- what I meant was that the number has no correlation to the actual captured resolution of the image. That is, you can input any number from 1 to 100000 and it won't change anything other than the size at which the printer will output the image by default.

QuoteOriginally posted by pingflood Quote
Technically correct, but how often does one consider DPI over print size? When's the last time you said to yourself "I better print this at 240dpi" rather than "I'd like this to be a 12x18 print"?
The only time you would say "I better print this at 240dpi" would be if you know that (say) 240dpi is the minimum print resolution for acceptable quality. That way, you would know that given certain image dimensions, you can print up to so-and-so many inches and still have acceptable quality.
02-23-2009, 05:24 AM   #66
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QuoteOriginally posted by Erik Quote
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.
Erik, this 72 dpi was valid for the original Macintosh screen in 1984, but not for any other screen or resolution. Since there was only one screen then and only one screen resolution available, Apple could say that they were truely WYSIWYG: if a font was 14 points on paper (= 14/72 of an inch), it was shown at the same size on that particular screen from 1984.

Since screens now come in varying sizes, can display various resolutions and, on top of that, the visual part of it can be scaled, this number has no meaning nowadays. Except that there is a convention that says: we'll pretend that our screen shows 96 pixels per inch (Windows) or 72 pixels per inch (Apple), although it does not, and if we represent a 14 point font on screen (14 point = 14/72 inch on paper), we will use 14/72 * 96 = 19 pixels for that on screen (Windows) or 14 pixels (Apple) (I'm talking about font height here).

So all to my best knowledge it's not about high or low resolution screens (it's just Windows/Apple), it has nothing to do with physical reality (except the 72 for that one rigid Macintosh screen in 1984: these were dots per inch on screen) and it's only for text fonts.

I'm fairly sure that we don't disagree, that you say the same thing as I do, but it's better not to link this text convention of 72/96 ??? (72/96 what? Not pixels, not dots per inches) to pictures and add to the confusion!
02-23-2009, 05:30 AM   #67
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QuoteOriginally posted by Andreas Quote
Erik, this 72 dpi was valid for the original Macintosh screen in 1984, but not for any other screen or resolution. Since there was only one screen then and only one screen resolution available, Apple could say that they were truely WYSIWYG: if a font was 14 points on paper (= 14/72 of an inch), it was shown at the same size on that particular screen from 1984.

Since screens now come in varying sizes, can display various resolutions and, on top of that, the visual part of it can be scaled, this number has no meaning nowadays. Except that there is a convention that says: we'll pretend that our screen shows 96 pixels per inch (Windows) or 72 pixels per inch (Apple), although it does not, and if we represent a 14 point font on screen (14 point = 14/72 inch on paper), we will use 14/72 * 96 = 19 pixels for that on screen (Windows) or 14 pixels (Apple) (I'm talking about font height here).

So all to my best knowledge it's not about high or low resolution screens (it's just Windows/Apple), it has nothing to do with physical reality (except the 72 for that one rigid Macintosh screen in 1984: these were dots per inch on screen) and it's only for text fonts.

I'm fairly sure that we don't disagree, that you say the same thing as I do, but it's better not to link this text convention of 72/96 ??? (72/96 what? Not pixels, not dots per inches) to pictures and add to the confusion!
Well, I agree. The "low/high resolution screen" thing I stated was a reference to the convention that Windows (used to?) have where you could select whether your screen was "96 dpi" or "72 dpi" and it would vary the size of screen elements including fonts to fit the supposed resolution. I am aware that these values are used for historical reasons only today; however, my point in the original post was that you CAN measure the real DPI value of a computer monitor; it is a valid way to use the term, it's just not very useful.
02-23-2009, 02:11 PM   #68
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FWIW, I just thought of another way of talking about the relevance of the dpi figure in the EXIF of of a digital image file:

Saying that an image stored in a digital file has a "native resolution" of X dpi is *exactly* like saying an image stored on a film negative has a "native print size" of YxZ inches.

If you're thinking of an image created by taking a picture of a real world scene, both statements are meaningless: you can print the negative at whatever size you want, just as you can print or display the digital image at whatever resolution you want. However, if you happen to be thinking of an image created by scanning a paper document or by shooting it on a copy stand, then the "native" resolution / size of the image *does* have meaning: it basically tells you how to reproduce the image in order to get back to the original size of the document. A *scanner* has a native resolution, to be sure. A camera does not.

02-23-2009, 02:36 PM   #69
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Since you asked...

QuoteOriginally posted by k100d Quote
OT but what did you used to teach?
... university level Public Relations, Mass Communications, Journalism and Public Relations (Writing), Special Events Publicity and Management; and at the Community College Level: Public Speaking, Small Group Communication, Interpersonal and Cross Cultural Communications, Intro to Speech for Film,
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02-23-2009, 03:32 PM   #70
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QuoteOriginally posted by soccerjoe5 Quote
Actually web browsers on computers are only capable of displaying a certain amount of colors, aka sRGB, and only at a certain ppi which is 72 ppi
Sorry, this is not true. Computer displays can be limited to a certain number colours (bit depths) and web browsers may use a limited palette of HTML safe colours, but when browsers display images they will use whatever amount of colours the display settings allow them to. Also, there are browsers (e.g., Firefox) which are capable of showing images with colour profiles other than sRGB correctly (in the case of Firefox you need to add a Colour Management add in).


QuoteOriginally posted by Marc Sabatella Quote
A *scanner* has a native resolution, to be sure. A camera does not.
A camera has a native resolution as well, which can be measured in LW/PH (line widths per picture height). Since the sensor has physical dimensions you can also express this figure as lines/mm.

Only the digital image is void of resolution because it has no physical dimensions.

Last edited by Class A; 02-23-2009 at 03:39 PM.
02-23-2009, 03:56 PM   #71
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QuoteOriginally posted by Class A Quote
Sorry, this is not true. Computer displays can be limited to a certain number colours (bit depths) and web browsers may use a limited palette of HTML safe colours, but when browsers display images they will use whatever amount of colours the display settings allow them to. Also, there are browsers (e.g., Firefox) which are capable of showing images with colour profiles other than sRGB correctly (in the case of Firefox you need to add a Colour Management add in).

The color management plugins are interesting and good news. However, I've always known that web browsers assume that photos are in sRGB as its standard, so it displays them as such. If a photo is in aRGB it will convert it the best it can. This is only when viewing a webpage in a browser.

But I don't have to prove anything to you, just sharing what I know
02-23-2009, 05:20 PM   #72
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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." 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.
Furshlugginer is spelled with two "g"s and an "i".

I'm not sure how "DPI" is spelled. Or spelt.

With all respect to the usual gang of idiots ....
02-23-2009, 06:24 PM   #73
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QuoteOriginally posted by glanglois Quote




Furshlugginer is spelled with two "g"s and an "i".
Actually, I think there isn't one "right" translation of it since it's Yiddish and using an entirely different alphabet.

'potrzebie' he did screw up though.
02-23-2009, 08:48 PM   #74
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Yiddish it's not...

QuoteOriginally posted by pingflood Quote
Actually, I think there isn't one "right" translation of it since it's Yiddish and using an entirely different alphabet.

'potrzebie' he did screw up though.
Sorry guys, but nobody with linguistic chops makes the claim that either "furshlugginer" or "portzebie" are derivative of anything other than Mad Magazine (c 1952). The final word on whether either/or was based on a couple of mistranslated Yiddish words (or another line is that both words started out Polish) would probably have been from Mad editor in chief Harvey Kurtzman who passed away in the mid 90s.
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02-23-2009, 09:59 PM   #75
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QuoteOriginally posted by Class A Quote
A camera has a native resolution as well, which can be measured in LW/PH (line widths per picture height). Since the sensor has physical dimensions you can also express this figure as lines/mm.
Granted, but this is *not* the same thing as the dpi figures being quoted.
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