Working with Images

Tue Feb 5 15:18:35 PST 2008

David...

This was not an attack on you. Please see my remarks embedded below.

Dennis...
****************************************************************************
At 02:07 PM 2/5/2008, you wrote:
>On Dennis Brunnenmeyer at dennisb at chronometrics.com wrote on 2/5/08 11:36
>AM:
>
> > Rant begins...
> > <snip>
> >
> > First of all, display devices, whether printers or monitors, have an upper
> > limit on their ability to resolve (print or display) image detail, which by
> > the way is what "resolution" is a measure of...meaningful detail. 
> The best my
> > aging but faithful laser printer can do is 600 dpi, while my uppity LCD
> > monitor can display up to 100 dpi, with its1600 x 1200 native 
> resolution on an
> > LCD panel that is exactly 16" wide x 12" tall."
>You are totally ignoring line screen (aka LPI) when printing. Using the
>formula will determine the quality of the output on a black-only laser
>printer:
>(Output Resolution/Screen Frequency)^2 [squared] +1 = total number of gray
>levels available to the printer.
>So a 600dpi printer at 100 LPI gives you only 37 levels of gray. For photos,
>you need around 200 levels of gray to look natural.
>
>For commercial offset printing, one should use the following guideline:
>PPI= LPI x 1.5. (Some use LPI x 2, but 1.5 is normally enough.)

I was referring to true image resolution. By resampling to a higher 
pixel-squared number, you have not increased the resolution of the 
image. No new detail is revealed that wasn't there before. However, I 
will grant that you may *enhance* the appearance when printing in 
this manner by falsifying the image to a degree.

> > You cannot see nor capture
> > anything and create a screenshot image with higher resolution 
> than the display
> > device......
>I think I said something similar to that.

I think you're probably right about that. However, several people 
have implied, that capturing a screen image at, say, 160 ppi gives 
more detail. This cannot be if the display resolution is set to 80 or 
100 dpi. The end result is that the same number of pixels are 
captured but with a higher ppi value, meaning as you have pointed out 
that the image is "physically" smaller.

> >
> > Most of you seem to appreciate this, but some of you think you can improve
> > resolution by artificial means. No, you cannot.
>I think I said something similar to that.

No, you said this: "One can, however, add extra resolution to the 
image, but that is usually detrimental
to the quality of the image."

Only the last half of this sentence is correct.

> >
> > A true measure of the resolution of an image is the original size 
> of the image
> > in total pixels, assuming it is true to begin with.
>I think I said something similar to that.

No reasonable person could disagree with that, and I think you are 
reasonable enough to have said that. Of course, in the case of color 
images, color depth counts too.

> >[Unfortunately, since the graphics card's resolution doesn't
> > match the native resolution of the LCD panel, the on-screen 
> picture is not as
> > crisp as it could be. This is a result of "aliasing" artifacts, 
> but that's a
> > topic for a different thread.]
>I believe you are confusing what you see on screen to what is actually being
>captured.

Actually, I'm not. The artifacts I see due to pixel aliasing on the 
screen are just annoying visual impairments specific to the display 
technology and not an indication of the quality of the image itself.

> >
> >
> >..... If I set the capture "resolution" to 160 ppi, then the
> > image will be half the physical size as it appeared on the 
> screen, BUT IT WILL
> > HAVE EXACTLY THE SAME NUMBER OF PIXELS. The resolution has not be 
> improved, as
> > no more detail has been added.
>I think I said something similar to that.

Yes, you did and you are correct.

> >
> >.... No new detail nor
> > image improvement can be added by interpolation.
>I think I said something similar to that.
>However, I suspect you have not used nearest neighbor interpolation too
>much.

"Improvement" in the sense that I meant it was intended to convey an 
improvement in actual accuracy. As you pointed out above, you can 
"enhance" some images this way by interpolating in new gray-scale or 
color values to yield a prettier but partially-false result. But you 
would NOT want to interpolate using any methodology in order to 
"enhance" a screen shot of a Windows dialog box. For the same reason, 
one should not save those kinds of screen shots as JPEG images.

> >
> > I have no idea what David meant by this statement:  "Again, referring to my
> > last post, monitor resolution only counts if
> > capturing an entire screen."
>I thought it was pretty clear. 1280x1040 is the same amount to X/Y pixel
>data on a 17 inch monitor, a 19 inch monitor, or a 20 inch monitor.

That's very true, but that's irrelevant to what I quoted above. Your 
sentence makes no sense.

> >
> > Flame away...
>I try not to flame or rant as I think it dilutes the message and reflects
>poorly on the messenger.

I don't like to rant either. I did it to draw attention to certain 
misleading concepts that are being promulgated in this thread.

>David Creamer
>I.D.E.A.S. - Results-Oriented Training
>http://www.IDEAStraining.com
>Adobe Certified Trainer & Expert (since 1995)
>Authorized Quark Training Provider (since 1988)
>Markzware, Enfocus, FileMaker Certified
>
>
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Dennis Brunnenmeyer
Director of Engineering
CEDAR RIDGE SYSTEMS
15019 Rattlesnake Road
Grass Valley, CA 95945-8710
Office: (530) 477-9015
Fax:  (530) 477-9085
Mobile: (530) 320-9025
eMail:  dennisb /at/ chronometrics /dot/ com