DPI: TRUTH OR LIE?

[Klaus Nordby]

Marcus, thanks for taking the time to spell out in detail why I'm right. Again.

:-)


K

[Klaus Nordby]

Marcus: "Okay, but what DPI is "correct" for the web?"

72, of course.
And 96, of course.

And so even this "standard" is quite hopeless!

Jontathan, I am VERY glad that current browsers do NOT mess with the display of my files, but just throw them up on the screen EXACTLY as I've lovingly created every pixel. I dread the day we get "smart" browsers which will start to fool around with things on their own - it would only be one more annoying complexity to deal with.

HOORAH for dumb, reliable browsers!


K

[User]

<BLOCKQUOTE><font size="-1">quote:</font><HR>Originally posted by Klaus Nordby:
Richard, what you're saying is of course mathematically correct. :-) But it's also TOTALLY useless - and only further serves to spread the confusion that screen/web images "really have" a DPI. If people think that your ruler-idea is relevant, then they will start to creat screen/web graphics with 92 and 98 and 88 and 101 DPI - ALL OF WHICH IS SENSELESS AND A COMPLETE WASTE OF TIME.<HR></BLOCKQUOTE>

I'd just like to qualify that a bit. Totally useless is a bit extreme.

If someone wants to print out something so it's the same size on screen as on paper, then the procedure I described is useful.

This method is also one of the things that helped me understand the relationship between 'resolution', what I see on my screen and what I see on paper after I've printed my images.

Of course, as has been mentioned several times in this thread, anything to do with image resolution is useless in the context of images for the web.

-Richard

[Klaus Nordby]

Marcus: "Incidentally, I kilobyte = 1000 bits"

No, I think it's actually 1024 - so all your subsequent math is a little "bit" off . . . Can Jonathan, Sean or some other ace programmer confirm or deny this itty-bitty fact?

Marcus: "But due to impurities in ink, it's very difficult to get true black from the primaries. So print systems "cheat" by throwing in black ink."

My friend, this is more semi-mythical, not too-well-informed stuff which we hear ALL the time . . . What if the three subtractive primaries could make for a solid black? For they certainly can - as they do in every normal photographic color print from Kodak! But even if this could be successfully done also in press-printing, there are actually other - and more important reasons - to use a black ink:

A. 300% solid CMY is NOT good for the press, as it makes for a sticky, slow-drying mess on the paper.
B. We almost always need black text in any print job - and to print black text with 300% CMY would be a registration-disaster!
C. Using a judicious amount of black ink in separations with GCR (Gray Component Replacement) makes it much easier to print neutral, grey-ish colors.
D. Finally, there are the economics: 300% CMY sucks up a lot of expensive color ink, whereas 100% black ink is dirt cheap.

So the reason for using a Black plate in printing is not just those semi-mythical "impurities in ink".


K
www.xaraxone.com/FeaturedArt/kn/
www.klausnordby.com/xara

[Klaus Nordby]

Richard: "Totally useless is a bit extreme."

I'm all in favor of being extreme.


K

[mgeduld]

Wow, Klaus! Thanks for the black ink info. Any more crap floating around the graphics world besides black ink, dpi and web safe colors?

I think you're right that a k is 1024bits (but what's 24 bits between friends? ;-)

In case anyone is interested, I posted a link to this discussion on metafilter.com. Things sometimes get a bit flame-ridden there, but there are a lot of webheads there, too, so I thought it would be interesting to get their input. Already, there are a couple of guys who are supporting the 72dpi myth.

Here's the link: http://www.metafilter.com/mefi/13016

Marcus Geduld
{ email me } { visit me }

[Bob C.]

This is a great thread and very helpful, thanks for taking the time to post.

I have been away for a few days and thought I would "pop in" for a quick "look see"! Oh Well [img]/infopop/emoticons/icon_biggrin.gif[/img]

Time well spent!

Bob C.

[Liorean]

I think what you people don't take into account is that there are two "inches", real-world inches, and so-called logical inches. A logical inch is always the same size in pixels at the same dpi, and that is an on-screen inch (this is the 'i' in 'dpi'). How many logical inches are used on your screen is determined by your screen resolution: 640x480 on a 15" screen, if I remember correctly, is equal to a real-world inch in size. But, a real-world inch is much smaller in size relative to a logical inch if you're using 640x480 resolution on a 19" screen.

But, these logical inches are corresponding to real-world inches when you print a thing. So, a logical inch is a real-world inch on paper.Now, what does this mean to printer and screen dpi's, what's the relation between them?

Well, because of Mac being the system where typesetting on computers traditionally developed, a system has been put in place, translating on-screen pixels to in-print pixels. This means, a 300dpi printer will print a 72dpi image at a 300/72 in-print pixel/on-screen pixel size, which means the printer will use several dots to build one pixel. This standard is locked in place, printer dpi/72 gives the screen to print dots-per-pixel ratio (Fonts etc. use this ratio) to match logical inches with real-world inches. If you in a such situation have a 96 dpi picture, this will mean you (in the 300 printer dpi case)get 300/96=3.125 ratio, when the ratio giving a real-world inch would be 300/72=4.16666....
Thus, images in 96 screen dpi are smaller in print than images in 72 dpi.

(3.125 dots per pixel gives more pixels per inch than a 4.16666... dots per pixel ratio, given a set dots per inch ratio)


(and let's hope I didn't fumble with the calculations there)

// Liorean

[mgeduld]

I've never heard of these creatures before. Can you site some source for this info?

Marcus Geduld
{ email me } { visit me }

[michaelward]

Actually a kilobyte is 8192 bits, or 1024 bytes [img]/infopop/emoticons/icon_wink.gif[/img]

Now about web safe colours... what's not web safe about the 216 pallette?



Michael Ward
http://LeighCenturions.net