Marah,

There are a few more things to consider when resampling an image, in
Painter or any other program, but I'll mostly talk about Painter here.

When you use the Canvas menu in Painter and choose Resize, the dialog
box will give you the option to change the Width and Height using
several options for units of measure (pixels, inches, CM, points, picas,
columns, or percent). The units of measure we most often deal with are
pixels or inches (in the U.S., that is).

Resolution (number of pixels per unit of measurement) can be set in
either pixels per inch or CM per inch.

CONSTRAIN FILE SIZE BOX CHECKED
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At the bottom of the dialog box, there's a check box to Constrain File
Size. If this box is checked, even though you change the Resolution the
total number of pixels in the file will remain the same. For example, if
your image is 500 pixels wide by 500 pixels high, with a Resolution of
300 ppi (pixels per inch) the total number of pixels will be 250,000:

500 x 500 = 250,000

With the Resolution set at 300 ppi (pixels per inch), the image
dimensions in inches are:

1.67 x 1.67 inches

Now, if you keep the Constrain File Size box checked (to have the total
number of pixels in the image remain the same) and change the Resolution
to 72 ppi (pixels per inch), with only 1.67 inches for Width and Height,
unless something changes, only some of the pixels will fit into the
resampled image. For instance, across the Width of the image only 120.24
pixels will fit:

1.67 inches x 72 ppi - 120.24 pixels

If nothing else changes, the total number of pixels in the image will
be:

120.24 x 120.24 = 14,457.6576 pixels

250,000 - 14,457.6576 = 235,542.3424 leftover pixels

Obviously, without something changing, all of the pixels won't fit
into the image, so what has to happen? Here's what:

The number of inches has to be increased to hold all the pixels. Let's
figure out how many inches are needed when the Resolution is changed to
72 ppi (each inch can only hold 72 pixels):

500 pixels divided by 72 pixels per inch = 6.944 inches

Now with the number of inches increased to 6.944 x 6.944, the total
number of pixels per inch remains 250,000, even though the Resolution
(number of pixels per inch) has been lowered from 300 ppi to 72 ppi.

NOTE: Fortunately, in the Resize dialog box, Painter figures out this
number of inches for you. It's important, though, to do the settings in
this in order: First type in the Resolution. Then change the unit of
measure for Width and Height from pixels to inches. Now you'll see the
number of inches for Width and Height change, for instance, from 1.67 to
6.944.

All of this is important to know because if you're trying to make your
file
smaller by reducing the Resolution, but you keep the Constrain File Size
box checked, the file is still going to be the same size.. not smaller.

CONSTRAIN FILE SIZE BOX NOT CHECKED
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What happens if you uncheck the Constrain File Size box? The image will
remain 1.67 x 1.67 inches and not only the file size will become
smaller, but the image will become much smaller (visually) on the
Painter screen. It will display at roughly 1.67 inches, visually,
depending on your screen resolution. On my screen, set at 1024 x 768,
when I use a ruler to measure the image it's approximately 1-15/32 x
1-15/32 inches.

That may be fine if what you wanted to display is a very small image.
It's not so fine if you wanted your image to look something like it did
on your Painter screen at 300 ppi.

When you see the original 500 x 500 pixel, 300 ppi image displayed on
your
Painter screen at 100% percent, it's displayed in pixels and the visual
size is partially dependant on whatever resolution your screen is set to
(mine is
set to 1024 x 768 and the image measured on the Painter screen with a
ruler is approximately 6-7/32 x 6-7/32 inches). On the web, it's much
the same. On my browser screen, the same image, not resampled to a
Resolution of 72 ppi and measured with a ruler is approximately the same
as what I measured on the Painter screen, around 6 1/2 x 6 1/2 inches.

Now, at least we know how to retain the visual size for display on the
Web. But how can we reduce the file size so the file is easy to upload
or send via e-mail and loads reasonably quickly on a web page?

REDUCING FILE SIZE WITHOUT REDUCING VISUAL SIZE
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This is best done by either choosing a lower quality when saving as a
JPG in Painter, or by using another program to optimize the image. I use
Fireworks and am able to get a large image rather drastically reduced in
file size while retaining pretty good visual quality (it still looks
pretty close to the original image quality).

If you don't have a program like Fireworks, do some testing using the
various quality settings in the JPG Encoding Quality dialog box when you
save the file as a JPG.

Important: To do this without losing your original image quality, first
save your in Painter's native format, RIFF. Then, as an excercise to
learn how this works and to choose the best file, make a folder to
contain some test files and save each test file to that folder.

Next, open the RIFF file in Painter and:

Save one time as a JPG, Quality: Excellent.
Save it a second time as a JPG, Quality: High.
Save it a third time as a JPG, Quality: Good.
Save it a fourth time as a JPG, Quality: Fair.

Now go to the folder and compare the file sizes.

Go back to Painter and use Ctrl/Command-H to hide all of your palettes,
then open all four of the JPG files and compare the visual quality. You
may have to use Ctrl/Command-+ (plus sign) to zoom in and compare
details and Ctrl/Command-- (minus sign) to zoom out again (or Ctrl/Command-1 to
open the Tools palette and use the Magnifier tool).

Choose the image that has a combination of least visual quality
loss/best file size reduction (this is a compromise we need to make when
using images on the Web). Remember, images on the Web are not super high
quality for three reasons:

The Web can only display 72 or 96 ppi anyway.
Large file sizes are slow to load and visitors don't want to hang around
and wait.
Large file sizes take up too much server space.

(Image dimensions, too, need to be kept at a reasonable size so that
visitors will be able to see them without using the scroll bars (very
annoying and detracts from the image viewing experience). The safest
maximum dimensions that anyone should be able to see are: 640 x 480. A
reasonable limit for most viewers would be 800 x 600.)

If anyone reading this message finds that I've misstated something, left
something out, or haven't made it clear enough, please jump in and
correct me/improve on what I've said as I don't want to misinform and
would like to learn better myself. Also, it would be great to have a
fine-tuned explanation of all this available for Painter users to refer
to, since the subject comes up so often. Thanks in advance. [img]/infopop/emoticons/icon_smile.gif[/img]

Marah.. I hope this helps and is not too confusing. If it is, just keep
the information and refer to it once in a while. In time, it will become
clearer. It's confusing to most of us, especially in the beginning.
And.. ask lots of questions.. ask lots of people.

Merry Christmas! Now I'm off to finish shopping!


Jinny Brown
http://www.pixelalley.com
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[This message was edited by Jinny Brown on December 21, 2000 at 10:54 AM.]

[This message was edited by Jinny Brown on December 21, 2000 at 10:55 AM.]