From: mflafeer@athena.mit.edu (Mohamed F. Lafeer)
Subject: Re: Mac multitasking?
Organization: Massachusetts Institute of Technology
Date: Mon, 14 Dec 1992 07:17:49 GMT

In article <_mj2nmp@rpi.edu> johnsd2@jec330.its.rpi.edu.its1 writes:
>In article 7041@athena.mit.edu, mflafeer@athena.mit.edu (Mohamed F. Lafeer) writes:
>>A couple of points about this discussion:
>>
>>Isn't "accurately" converting a hand-drawn 72dpi picture to 300dpi sort of 
>>like taking a digital recording done at 22kHz and converting it to 44kHz?
>>In other words, if the drawing is hand-drawn how can you add more detail
>>to the picture? Doesn't that mean making arbitrary decisions. The example
>>that Eric gives just shows that Apple and NeXT make different arbitrary
>>decisions.
>
>In this case, we are drawing a circle and a line- the bitmaps are only
>approximations, but if you increase the resoluion you CAN get more
>details, because the computer knows what "supposed" to be there.
>
>>The conversion from screen res to printer res only works well for mathematical
>>constructs. Lines drawn on the Mac at 72dpi print smoothly at 300dpi.
>>Same for Circles. And it you define a true tangent in Claris CAD for instance,
>>it will print correctly at 300dpi. The fact that you can go up to a NeXT and
>>eyeball a tangent at 90dpi and have it be a tangent at 400dpi means nothing
>>to me. 
>
>This case we have a ->hand draw<- tangent that looks right at 72 dpi..
>will it looke right at 300 dpi or not?
>
>>In short, device resolution independent imaging only makes sense with
>>mathematical constructs. 
>
>Such as what we have.. :)
>
>>Furthermore, who cares? In practice, the conversion between quickdraw and
>>postscript isn't a problem. 
>
>Hmmm. I hope so, but Eric says that it IS a problem. I think. Im not
>quite sure.
>
>>Oh, and by the way, the price of the NeXT printer was a big deal two years
>>ago. It really isn't any more in the age of cheap Postscript II RISC powered
>>laser printers.
>
>I dont know about this bit.
>

I'm referring to the Apple Personal Laserwriter NTR, for example.

>>Remember, Mac OS may not be the most sophisticated OS around, but it has 
>>grown quite well maintaining compatibility with 4 generations of Motorola
>>processors, eight years of development from thousands of developers, and 
>>millions of Macs, many of which are quite affordable. These features are
>>at least as important as the implementation details we nerds argue about on
>>the net.
>
>I agree heartily. (surprise surprise)
>
>But the implementation details do matter too.
>And they are more fun to argue about. :)
>
>
>---
>			- Dan Johnson
>And God said "Jeeze, this is dull"... and it *WAS* dull. Genesis 0:0
>
>These opinions have had all identifiying marks removed, and are untraceable.
>You'll never know whose they are.

Let me try and make my point about the tangent thing again.

Imagine a circle and two lines. Line A is tangent to the circle. Line B lies
10 microns away from the circle.

Now, suppose you have a 72dpi screen.

Draw the circle and the two lines. You will draw the lines exactly the same
way. Why? Because 10 microns doesn't mean anything at 72dpi.

Now, suppose you had a million trillion dpi printer. Now the computer or
printer must decide when it prints your line whether or not you meant for
the line to be really tangent or 10 microns away from the circle. It has to
determine that from the way you drew the line. But, you drew line A and line
B exactly the same way.

Now suppose that we're not talking about 10 microns. Suppose the distance is
1/300 of an inch. At 72dpi, the line would be tangent. At 300 dpi the line
should be exactly one pixel away from the circle. Not tangent to the circle.

On other words, tangency cannot be assumed by the software just because I
line happens to be tangent at a certain resolution. The reliable way to
define true tangency is to let the software know in no uncertain terms that
this line is tangent. In Claris CAD, for instance, you would use the tangent
tool. On the Mac, if you use the tangent tool, the line will be tangent at
any resolution.

If I go to a 72dpi screen and just eyeball a circle and a line with 1 pixel
in common between a circle and a line, then print that picture at 300dpi, it
is not necessarily correct for the computer to draw that line perfectly
tangent to the circle. Maybe I meant for that line to be 1/300 of an inch
away. If you want tangency, specify it.

-M.Firoze Lafeer
mflafeer@athena.mit.edu