Page 166 - Enhancing CAD Drawings with Photoshop

4386.book Page 150 Monday, November 15, 2004 3:27 PM

150 CHAPTER 5 PRESENTING PLANS

Figure 5.14
Image size and
resolution

The History of “Screen Resolution”
There is actually no such thing as standard screen resolution, but this concept has been kicking around
since 1984 and has influenced countless millions! Back when Apple introduced its first Macintosh com-
puter, it sported a monitor that actually had 72 pixels per inch on its 9˝ screen. Now it was a lucky coinci-
dence that text fonts are traditionally measured in point sizes that are fractions of 1/72˝. For example,
a 12-point font was 12/72˝ in predigital typography. So Apple’s great marketing scheme was what you see
is what you get (WYSIWYG) because the size of the text on the monitor was the same absolute size the text
was when it was printed. This has never been true since because the size of pixels varies on every monitor.
Monitors are measured in pixels, not resolution; most actually have resolutions anywhere from 60–150 pix-
els per inch of viewable screen area.
To complicate things, Microsoft later used 96 pixels as its measure of the logical inch in Windows. The log-
ical inch is just an arbitrary measurement that the operating systems uses to calculate font size on screen,
but has no bearing on the actual text size because every monitor is different.
Because of this legacy, most web designers use either 72 or 96 ppi when designing for the screen. The irony
is that these measurements are arbitrary, and images and text are actually displayed in different sizes on
every monitor.
We are using a resolution of 96 ppi because it matches the image that was plotted at 1:1 with 1/8˝ graphic
scale. It is purely a coincidence that 96 ppi is also the measurement of the logical inch in Windows (also
known as screen resolution).

8. In the Image Size dialog box, change Resolution from 72 to 96 pixels/inch. Click OK. Figure 5.15
shows the resulting relationship between the printed size (in the ruler) and the building. The
24´ wall now correctly measures 3˝ on the printed page. The image is now precisely in 1/8˝
scale.

NOTE Rule to remember: When you print at 1:1 (meaning 1 inch = 1 pixel) in AutoCAD, setting the
resolution to 96 pixels/inch in Photoshop produces a 1/8˝ scale image.