Image Resolution and file size
Resolution is worth mentioning because it causes so many problems in the prepress department. Any image you want to print must be a minimum of 300 DPI at 100% of its actual size. If you pull an image off a website, and it is 4 in. x 4 in. and 72 DPI (the typical web resolution), when you place it in your page layout, it must be sized to 24% of its original size, or .96 in. x .96 in. in order to be at the correct resolution for printing.
There is absolutely no way to take a low resolution image and make it look like a high resolution image. Interpolating a file to a higher resolution makes the image look like an image that was interpolated up to a higher resolution to improve it’s appearance. One low resolution image can make a whole brochure look cheap. Make sure all the images you provide are the correct resolution for their output size.
Here I have pasted three different file sizes of the same image. I adjusted their dimensions so they would each be about the same size “on this page”. Below each fish pic is the Adobe Photoshop screen shot showing the image “dimensions” in pixels and inches.
Specify and use correct file formats
Each software program creates a native file format that it “gets along with” best. For Adobe Photoshop, that would be bit-mapped files like TIFF, JPG, and PNG. For Adobe Illustrator, it is EPS files. Adobe InDesign is a composition program that can accept nearly any file type for inclusion into a document that will be printed or published to the web.
Some file formats work well for print, and some work best for the web. Here are some common file types and their best uses:
- TIFF: for high-resolution photographs and scanned graphics
- EPS: for infinite scalability
- PDF: for high-resolution printing when properly saved with embedded fonts and bleeds, etc.
- JPG: for many compression options and fast loading
- PNG: for more image depth. The trade-off is its large file size, no CMYK: RGB only.
- GIF: limited color (256 only) but very fast loading
Don’t use image compression unless you absolutely have to. Every time an image is compressed (when it is saved) and uncompressed (when it is opened), it rewrites the data in the file and leaves little artifacts/noise in the image.
Compression is left over from the days when a 44 MB (yes, that’s MB, not GB or TB) Syquest drive cost $200. Nowadays, storage is cheap. Compression works well for the web, but it isn’t necessary for anything else. For example, Tiff files and images are not compressed. Jpeg files and images are. Here is an example of how to save a TIFF image without compression.
If you have had an experience with resolution or file types that you found helpful, or from which you learned, please share it below. Thanks!