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 Alan Justice 08-14-2004 09:30 PM

Monitor "resolution"

I will buy a new computer for Photoshopping scanned slides for printing, and
would like to know what is important for monitor characteristics. I'm
confused about the terminology for "dot pitch" versus "pixels" versus
"resolution."

Pixels. Picture elements. Fine. When I look at one of my CRT monitors (12
years old) very close up, I see red, green, and blue dots. Is each dot a
pixel? Or is it a pixel a group of 3? When I look at a newer monitor (6
years old) I see vertical lines of red, green, and blue. But each line
appears wavy from top to bottom at regular intervals (sine wave of
brightness?) . I calculate there are about 1600 sets of 3 going across, and
it's a 1600x1200 resolution monitor. So a pixel must be a group of 3 lines
across and one wave up & down. Fine. When I set it to 800x600, does that
mean that 2 adjacent groups of the 3 colors (pixel?) will be displayed the
same? And how does it work if I set it to 1280x1024. Doesn't it have to be
an even divisor of 1600x1200?

Dot pitch. Doesn't this determine resolution? The smaller the dp (distance
between pixels), the higher the resolution, right? Then why can two 19"
monitors from the same manufacturer, both with 0.25 mm dp, have different
resolutions (1600x1200 vs. 1920x1440)?

And how does all this affect ability to determine image sharpness in
Photoshop? Can't I just enlarge the image on screen to see its inherent
sharpness, or is it only with a high resolution monitor that I could tell
the difference?

--
- Alan Justice

 Paul D. DeRocco 08-15-2004 01:34 AM

Re: Monitor "resolution"

> "Alan Justice" <spam@spamspamspam.spam> wrote
>
> Pixels. Picture elements. Fine. When I look at one of my CRT monitors

(12
> years old) very close up, I see red, green, and blue dots. Is each dot a
> pixel? Or is it a pixel a group of 3? When I look at a newer monitor (6
> years old) I see vertical lines of red, green, and blue. But each line
> appears wavy from top to bottom at regular intervals (sine wave of
> brightness?) . I calculate there are about 1600 sets of 3 going across,

and
> it's a 1600x1200 resolution monitor. So a pixel must be a group of 3

lines
> across and one wave up & down. Fine. When I set it to 800x600, does that
> mean that 2 adjacent groups of the 3 colors (pixel?) will be displayed the
> same? And how does it work if I set it to 1280x1024. Doesn't it have to

be
> an even divisor of 1600x1200?

On an LCD, each RGB cluster is a pixel. On a CRT, the pixels are larger than
the dot clusters, and somewhat intentionally blurry. The pixel rows on a CRT
are determined by where the electron beams scan, and the columns are
determined by how fast the digital to analog converter values change during
the scan. The pixels therefore have nothing to do with the dot cluster size,
except that the latter places a limit on how small the pixels can possibly
be before they no longer land on all three colors.

> Dot pitch. Doesn't this determine resolution? The smaller the dp

(distance
> between pixels), the higher the resolution, right? Then why can two 19"
> monitors from the same manufacturer, both with 0.25 mm dp, have different
> resolutions (1600x1200 vs. 1920x1440)?

Probably a scan rate limitation. In general, you want to keep the vertical
scan rate up above 70Hz. The threshold below which the eye starts to detect
flicker is quite sharp, and varies from person to person, and is also quite
a bit higher for peripheral vision. I can't see flicker at 72Hz, but can at
68Hz.

> And how does all this affect ability to determine image sharpness in
> Photoshop? Can't I just enlarge the image on screen to see its inherent
> sharpness, or is it only with a high resolution monitor that I could tell
> the difference?

Of course you can enlarge the image. If you view at 100%, then you may not
see the entire image at once, but you're seeing one image pixel per screen
pixel. If the monitor (or your eyes) are a little blurry, going up to 200%
or 300% will make it even easier to see how sharp the image is.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@ix.netcom.com

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