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Archiver > TMG > 2006-09 > 1157476787


From: Stuart Armstrong <>
Subject: Re: [TMG] Exhibit question
Date: Tue, 5 Sep 2006 11:19:47 -0600
References: <20060905152006.26885.qmail@webmail3.knology.net>
In-Reply-To: <20060905152006.26885.qmail@webmail3.knology.net>


John,

I remember having images that did not fill the screen, but not
recently. I think it is because I resized many of them in an external
program. I don't remember now whether the display size is determined
by the actual pixel dimensions or by the internal print size or
resolution setting.

Picture size is a confusing issue which I haven't seen adequately
addressed anywhere. And I'm not sure I can give it a fair treatment,
but I want to try.

How big a picture displays or prints depends upon the program doing
the displaying or printing.

Image files have somewhere in their coding a parameter which
represents the ratio between how many pixels there are and how that
relates to INTENDED physical size for printing or viewing. Some
programs may express that value as a computed size such as 5 x 7
inches or 8 x 10, while other programs express it as a ratio such as
200 dpi (dots per inch). And it appears from my observation that that
parameter for most image formats is optional.

The dpi value represents only the INTENDED physical resolution of the
image for viewing or printing purposes. So if the image is 100 dpi and
contains 500 x 700 pixels, then it is INTENDED to print or display at
5 x 7 inches. But that doesn't necessarily mean it will.

The question is, how does the program that is displaying or
printing the image treat dpi values? Frankly, many programs just
ignore them. Many print programs determine print size by other factors
such as page layout, or allow the user to enter a physical size that
over-rides the internal dpi value. Images exported from a TMG report
to MSWord are initially sized according to the dpi value, but then you
can drag the sizing handles to any size you want.

What happens when you re-size an image? It is possible to resize an
image without re-sampling. Programs such as the popular freebie Irfan
View can batch re-size a whole folder full of images quickly in one
pass, converting each image to say 300 dpi or any other chosen value.
The printed or displayed size will then depend on how many inches high
and wide that computes to for the number of pixels in the image,
assuming the dpi value is even consulted.

As I said, I don't remember whether TMG consults the dpi parameter
when displaying the image or not. If it does, then changing the dpi to
a smaller value will enlarge the image. If it only pays attention to
the number of pixels, then you will need to re-sample the image so
that it contains more pixels (and more data and larger file size).
That process can also be done with external programs or from
within TMG.

The key point to remember is that whenever you re-size an image in any
program, whether shrinking or enlarging, be sure you understand what
the program is going to do to the image. Is it going to simply change
or set the dpi parameter (without touching the data)?, or is it going
to re-sample the image data itself?

Sometimes it is not at all clear which method the program is going to
use. Does changing the size to 5 x 7 inches mean it is going to change
the dpi setting so that the resulting dimension is 5 x 7? Or does it
mean that it is going to keep the dpi setting and re-sample the data?

TMG's re-size function has you enter the actual pixels you want to
re-size it to, implying that it is going to re-sample the data. That
means if you make it smaller you are going to throw away information
and degrade the quality of the image; and if you make it larger you
are going to increase the file size without increasing the quality. I
wish TMG would allow you to simply fiddle with the dpi setting.


How many dpi do you need? DPI required for an acceptable image is
inversely proportional to the viewing distance. A book page viewed at
20 inches needs a lot more DPI than a framed photo high on the wall in
a photo gallery. Printed portraits such as might commonly be hung on
the wall of your home or displayed on a desk or in an album, need a
resolution of about 200-250 dpi. A higher resolution will not be
appreciated unless you hold the picture close to your face. Then you
can definitely see the difference up to 600, 1200 or even more, but
you don't usually look at pictures that way. Detailed maps might
benefit from higher resolution, because you might expect to examine
them very closely.

Incidentally, I love portraits. You can recognize a face even with
very poor resolution, and many studio portraits soften and blur
deliberately (because most people look better that way) to the
equivalent of perhaps 100 dpi. But a portrait of a face that fills the
frame at 6 megapixels fairly sizzles with detail. I have also found
that the only part of a human face that really needs detail is the
eyes.

Now I'd better stop before I drift too far afield ...


Comments welcome.


Tuesday, September 5, 2006, 9:20:06 AM, you wrote:

> Is there any way to set an exhibit photo so that it fills the display box?
> I have just recently started adding photos to TMG, but I'm disappointed
> that they look so small on screen. I'm not referring to any kind of
> printout, but only to the exhibit section of my on screen layout.


> Thanks!
> John



--
Best regards,
Stuart mailto:


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