A few questions about using photos in Illustrator

[mellimello]

hi,

i use photos in illustrator as backgrounds for the images that i draw. i'm having a few issues:
1. i'm not certain how large i can print the entire artwork and thus, how large i can make the artboard, because i dont know at what point the photo will start losing its quality. Does anyone know how i can find out what the maximum printing size is of a photo? i.e. my digi cam takes photos at 2592 x 1944 for example, so how large can i print this file?
2. obviously photos can be very heavy and if i want to use more than one, things can become very slow and tedious. is there a way to change the format of the photo, let's say in photoshop or something, so that the image quality is kept while the image itself is not so heavy?

thanks a lot to anyone who can help or who has some ideas. if there are any resources that you might recommend in terms of books or online tutorials, that would be great.

thanks again,

mel

 

[jmgalvin]

Just look at the PRINT size in photoshop at a minimum of 300dpi. Don't worry about pixels, except dpi, when working for print. You cannot enlarge a photo past the maximum you import from another source.

300 dpi jpeg, at highest quality, or 300 dpi pdf are the best bets for reducing file size with reducing quality. Just remember to keep your original pic in case editing is needed later.


Using OSX 10.3.9 on a G4 & G5

 

[eugenetyson]

When you insert a photo you can view it's ppi in the control panel at the top, it will say something like "300 ppi". When you resize the image you will see that value change. You are aiming for the 300 ppi mark.

As for the image size. You can resize the image in
illustrator and look at the ppi when you resize it, once it's around 225ppi (150 lpi printing) or higher you can print it. But at that size and no bigger, the bigger you make it the smaller the ppi gets, and vice versa.

You can open the files and save them as .jpg in photoshop and place into illustrator a jpg is a compressed file, it's not lossy, meaning that it loses quality the more times it's saved and it loses a lot of image data when saved as a jpg, but at 300 ppi it is not noticeable to the naked eye.

As for your 2592 x 1944 image. That's pixels.

Low resolution is considered by many as 72 ppi, that's pixels per inch and probably what your camera stores images at 72 ppi/dpi.

One point equals 1/72 of an inch. So, for a 72 dpi image, 1 point = 1 pixel.

So it's safe to say that 2592 pixels = 2592 points @ 72 ppi

and 1944 pixels = 1944 points @ 72 ppi

I know that there are 72 points in an inch

so 2592 points = 36 inches
and 1944 points = 27 inches

So your image as 72 ppi is 36 inches x 27 inches

if your image is twice 72, 144 ppi then your image size is 18 x 13.5 inches.

If it's 4 times 72 ppi, then it's 288 ppi and that gives you a 9 x 6.75 inch image.

And you can work it out yourself for a 300 ppi image.

So basically for your image to print at good quality it must be 300 ppi or more (you could get away with 225 ppi if printing at 150lpi, but that's another story). If your image is not 300 ppi at 100%, say you double the size of the oringinal image (32 x 27 inches) to 64 inches x 54 inches of a 300 ppi image then it's ppi changes to 150ppi.

The good news is photoshop can do all the calculations for you. In Image>Resize and then turn off resample, and make the image 300 ppi, the physical size of the image will change to give you the correct dimensions for placing at 100% at 300 ppi.

PPI and DPI are interchangable, usally PPI is restricted to screen and monitor values and DPI is usually reserved for actual printed.