On Wed, 13 Jul 2005 20:40:30 GMT, "patrick"
wrote:
OK, I’ll keep an open mind, Owamanga. It is still my understanding that ppi refers to the density of the pixels on the monitor and that dpi refers to the density of the pixels at the printer.
Okay, yes, you can look at it that way.
A pixel is a pixel. You can spread those pixels on the monitor at 72ppi or 96 ppi, or whatever. I’m sure that is the terminology I’ve read in the literature. Same with the printer, except that trade usiage is dpi ain the printing business.
And her lies the problem. There is no 1:1 correlation between a printed dot and an image pixel. A printed dot can be at most, one of 16 different colors. Your image pixel can be one of 16 million different colors. How can the printer possibly represent 16 million different possible pixel colors when in a single dot, it can only spray:
Yellow or no Yellow,
Magenta or no Magenta,
Cyan or no Cyan,
Black or no Black
(16 different combinations). I’m simplifying here to demonstrate the point, there are of course a number of other advancements such as variable dot size, more color ink tanks and the affect of clusters of pixels of similar color. On the other hand, one could argue that if you spray black onto any mixture of CYM, you’ll get black, so the number of possible colors a single dot can be is only 9.
PPI = DPI in one situation only. When your source image is a 2-bit monochromatic image, ie it contains only 2 colors (say, black and white for example) and no shades of gray. Then, the printer can truly represent an image pixel with a single dot. For full-color prints, the printer needs 16, 32 or more dots per pixel, that when viewed together, our eyes merge to represent the ‘true’ color of the image pixel.
That having been said, this only applies to dithering devices (such as ink-jets and laser-printers). Continuous tone printers (some of the little 4×6 photo dye-sub printers) are not limited to 9 or 16 colors per dot, it can mix ink, just as your monitor mixes light and lay down a single ‘dot’ that can be one of several million different colors.
Same is true of digital wet printers, they can fire lasers at different intensities onto photo-sensitive paper so that each ‘dot’ (or printed pixel) can truly be one of millions of colors.
So, an ink jet dpi resolution of 300 dpi is no where near as good as a digital wet system or dye-sub printer of the same resolution.
(Here’s a dye-sub if you’ve never seen one)
http://www.steves-digicams.com/2005_reviews/cp600.html Don’t run out and buy one though – From my own experience, a properly functioning ink-jet still wins. i.e. Resolution *is not that important* compared to a decent gamut. Today I have access to both but generally use neither, preferring to do digital wet prints from www.mpix.com instead.
They both refer to the density at which the pixels are
displayed or printed. And, in the photo editing community on the Internet, they are being used interchangeably (even if wrongly to the traditional purist).
This *isn’t* a purist thing. They are simply *not* comparable. A group of three RGB CRT dots that together, when illuminated provide one pixel capable of being any of 16 million colors can’t be compared to a grungy little inkjet dot that can be one of 16 (half of those being black).
At any rate, thanks for your patience in trying to get through to me. Some night I may wake up with a great white light experience and see it all. Not today, though. Sorry.
Don’t worry at all. It’s not you. It’s an *extremely* common misconception. It’s been drummed into the population from all angles – magazines, websites, the dude who’s still picking his spots at circuit city, and of course even this NG.
Unlike other places where marketing ‘cons’ people, (How many bytes in a megabyte – a 21" screen that isn’t 21" in any dimension even if you wrap a tape measure round it etc – processor speeds described in clock cycles rather than instructions per second – disk space described in it’s unformatted capacity etc), this one is a biggie.
Always enjoy your inputs, Owamanga.
Well, that *is* strange.
😉
—
Owamanga!
http://www.pbase.com/owamanga