Expert: Glen Demers - 10/4/2010

Question
Hi Glen,

I have created a banner about 2m long and 750wide in Photoshop CS5. I started off working in 72dpi as it was easier to work with. Now that i've changed it to 300 dpi, the file size is fairly big at 640mb as compared to 35mb before - Is that normal?

Also what would you say is the best format to save in - i don't really want to go Tiff because then i fear the size will double - which would prob cause CS5 and our servers to crash.

I've never really done anything of this magnitude. Any info will be greatly appreciated,

Thanks.  

Answer
Hi Daniel,

The size is determined by the resolution x the dimensions of your document x the color space. So a 300 dpi image will be over 4 times bigger than a 72 dpi image, a CMYK image will be four times bigger than a Grayscale image and 25% bigger than RGB. For an excellent article on resolution click here: http://www.bestprintingonline.com/resolution.htm

Web graphics are usually done at 72 dpi RGB which is the resolution and color space of most monitors. Print requires resolutions up to 300 dpi in CMYK mode, which is 1.5 - 2 times the screen line ruling on the plates used for offset printing. For signs and specialized graphics, check with your vendor about their file resolution, color space and format requirements

Tiff format will not add any file size to your image, but will not compress it either, however, each layer you add will add to the size of the file. JPEG format will reduce the file size but it is a lossy compression scheme, meaning, the quality of the image will suffer each time you open and save in this format. When you open a JPEG file it expands to it's tiff file size, so it won't save you anything just working on your desktop or server.

I usually save original images as PSD or Flattened TIFF format. I will make a JPEG copy of an image to upload or e-mail.

Hope this helps,
Glen Demers
Adobe Certified Expert, Photoshop 7
Prepress Technician, Best Printing Online
www.bestprintingonline.com

For more Photoshop tips please visit our help pages here: http://www.bestprintingonline.com/photoshop.htm