Franklin wrote:
Jim, thank you for a detailed reply. My need is also to **print**
the GIF (which is of a text document) at normal size as well as to
view it at normal size on the PC screen.
Let me explain some more .... My experience is that if I shrink or
enlarge a GIF then even if the change in size is relatively small
then the new GIF can be seen on the screen to be of noticeably lower
quality.
In your reply you have explained more about this and told me how to
predict dimensions and to accommodate dpi settings. But what about
PRINTING?
As CSM1 indicated in another reply.. For printing, just print
at the same DPI you scanned the image at.
Scan a one inch wide document at 300 DPI, you get an image
that's 300 pixels across. Print the 300 pixels at 300 DPI
and you get a one inch wide image on paper. Print at
150 DPI and you get a 2 inch image. 600 DPI will give
you a 1/2 inch image.
The problem is if you view this 300 pixel image on your monitor
(that uses 85 pixels to make each inch) it will be 3.5 inches
wide. (300 pixels / 85 DPI = 3.5 inches).
Here's where the DPI setting of an image comes into play.
The DPI of an image has nothing to do with how big it looks
on a monitor and everything to do with how big it prints
on paper.
If you take your 300 pixel image and sample it down to
85 pixels, then it will appear one inch wide on a monitor
that uses 85 pixels to make an inch.
If you set the DPI of this image to 85, then it will print
at one inch. (Setting the image to 85 DPI is telling the
printer to spread 85 pixels across each inch of paper.
Since the image is 85 pixels across, then it will be one inch
wide. It has to be
So.. Scan at a high resolution. Sample the resulting
image so the pixels match your monitor's resolution.
Then, change the DPI of the image file so the image prints
at the correct width/height.
Example:
By measuring the width of a monitor and dividing the
inches by the monitor's resolution, you get the
pixels per inch the monitor displays. Let's
say it calculates to 80 PPI.
You have a 6 inch wide document and you want it to be
6 inches wide on your monitor and you want it to be
6 inches wide when you print it.
Scan the document at 300 DPI. This will result in
a file that's 6 x 300 = 1800 pixels wide.
Sample the image to fit the screen. Since in this
example 80 pixels make up an inch of the screen,
you have to make the image 80 x 6 = 480 pixels
wide.
If you want this 480 pixel image to print on paper
at 6 inches, it has to be set to 80 DPI. Setting
it to 80 DPI tells the printer to spread 80 pixels
across each inch of paper. Since there are 480
pixels, the resulting print will be 6 inches wide.
The only downside to doing this is that you will
have a low resolution print. At 80 DPI, you lose
a lot of detail.
Unfortunatley, this is the only way you can have an
image appear the same size on your monitor AND on
your printer. If you want to print at high resolution,
then you'll have to scale the image on your monitor.
Here are a couple of web sites that explain the
same thing.. Perhaps a bit better
http://www.scantips.com/
http://www.larry-bolch.com/dpi-revealed/
So I figure that I should print the GIF at its "normal" size in order
to avoid any noticeable reduction in quality. As my original post
here mentions, I have tried to do this by (1) changing Twain settings
as well as by (2) using resizing utilities. But I have had poor
results. Maybe I am not using these applications correctly?
As an alternative approach, perhaps there are image file formats
which are better suited to resizing operations than GIF is?
Twain settings should have nothing to do with how the image looks.
What software are you using to size the images ?
Also.. If you don't need transparent backgrounds, there's no real
advantage to using GIF.. I'd use JPEG. The files use up less
disk space, and you have a lot more colors (This makes it better for
displaying photo images).
GIF can only display a maximum of 256 colors. For photos, this
results in a 'posterized' effect because color transitions aren't
smooth. JPEG images give you 16 million colors that result in
'photo quality' images.