newbie question regarding resolution, dpi and print sizing

[logik]

hey all....
im quite new to graphic design and photoshop. im having a little
difficulty with a couple of things and am wondering if anyone can make
things a little clearer.

ive been asked by a friend to see if i can come up with a couple of
designs for his recent novel (historical fiction on the great war).
im certainly interested in trying and have tinkered with a number of
ideas so far. my idea is to combine photos of the time with a 3d
design image im creating in 3d studio max. ive been told that the
image must be at least 300dpi and ive also been told the page format.
im using a program called terragen that creates photo realistic
landscape scenes but have descovered that it only outputs to 72 dpi.
now this is where i need help. from my understanding if you have an
image that is a certain dpi and reduce its dimensions (resolution) you
increase its dpi. is this correct??? therefore what is the formula
of working out how big i have to render an image to so that then when
i resize it the dpi increases to over 300???

secondly.....ive been using a canvas the exact dimensions as the
format of the book. is it best to do this this way or work bigger. i
have a number of photos and always seem to be resizing them to fit. i
dont know if its just my moniter but when i do this to an image a bit
it doesnt look as good. is it a good idea to work with a much larger
canvas but keeping the length by width ratio of the end product
dimensions.....
thanks...
logik

[Tacit]

>ive been told that the
>image must be at least 300dpi and ive also been told the page format.
>im using a program called terragen that creates photo realistic
>landscape scenes but have descovered that it only outputs to 72 dpi.
>now this is where i need help. from my understanding if you have an
>image that is a certain dpi and reduce its dimensions (resolution) you
>increase its dpi. is this correct???

Yes.

Resolution, image size, and file size are all related.

Think of your image like a tile mosaic. Each tile is a single pixel.

Resolution determines how big those tiles are--that is, how big each pixel is.
If an image is 72 pixels per inch, then each "tile" is 1/72 of an inch across.
Likewise, if the image is 300 pixels per inch, the tiles are 1/300 of an inch
across.

Resolution and print size are related in a very simple way: The number of
tiles, multiplied by the size of each tile, gives you the total size of the
mosaic. If a tile mosaic is 100 tiles wide, and each tile is half an inch
across, then the mosaic is 50 inches wide.

Likewise, if you have an image which is 300 pixels per inch, and it's 600
pixels wide, it is 2 inches wide.

Similarly, a picture which is ten inches wide and is at 300 pixels per inch
must be 3,000 pixels wide.

When you create an image for printed output, it is not always true that the
higher the resolution is, the better. An ink-jet printer does not print a
better image from a 600 pixel per inch image than it does from a 300 pixel per
inch image, for a variety of reasons. Similarly, an image printed on a printing
press (say, in a magazine) does not benefit from a very high resolution; all
images printed on a press are broken up into halftone dots, and the ideal
resolution depends on how fine those halftone dots are.

When you look at an image on your screen, the image will seem to be very large,
because what Photoshop says is "100%" magnification is not the size the image
will print! When Photoshop shows you something at 100% magnification, what it
means is that one pixel on your screen equals one pixel in your image; you are
seeing "100%" of the number of pixels that will fit on your screen. An image
that is two inches wide at 600 pixels per inch is 1,200 pixels wide--it will
more than fill your 1,024x768-pixel monitor, even though when it prints out it
will only be matchbook sized.

You can change the image size of an image in two ways: by using interpolation,
which changes the number of pixels, or by not interpolating, which leaves the
number of pixels the same but changes the size of each pixel.

For example, let us suppose that you have an image that is 10 inches wide and
300 pixels per inch. It is 3,000 pixels wide.

If you shrink it to 5 inches wide, but you have interpolation turned off, the
number of pixels will not change. The image is still 3,000 pixels wide, but it
is only 5 inches wide; therefore, it is now 600 pixels per inch.

Now, let's suppose you shrink the same image to 5 inches wide using
interpolation. Photoshop will change the number of pixels. The image will now
be 5 inches wide, and it will still be 300 pixels per inch, so it will now be
1,500 pixels across, instead of 3,000 pixels across.

>secondly.....ive been using a canvas the exact dimensions as the
>format of the book. is it best to do this this way or work bigger.

For offset printing, make your canvas 1/8" bigger than the book all the way
around (that is, add an eighth of an inch to the top, bottom, left, and right).
This extra space is called "bleed." Because no press and no die cutter can line
up and print an image precisely, this bleed give the press operator the
necessary margin for error when operating the cutter.

------
Literary forums; Onyx, a game of sexual exploration; Xero, the industrial
magazine of art, fiction and photography; fine-art photo gallery--all at
http://www.xeromag.com/franklin.html

[logik]

thanks heaps for your help tacit....ive had a little difficulty
getting this down but found your answer a great help.....

cheers mate :)

[Clay White]

Just do everything based on pixel count. 10 inches at 72 ppi is equal
to 1 inch at 720 ppi. So if you page is 7 inches wide and you need
300ppi then your document needs to be 2100 pixels wide at 72 ppi that
is 2100/72=about 30 inches wide.

logik <chocob...@yahoo.com> wrote in message news:<lnp1lt80219krvkrj...@4ax.com>...