Dots-per-inch (dpi)

[BigAl]

"When editing my pictures and resizing them, they are normally 72 dpi, and I think when they are this size then when I post one on the site your able to magnify it to full size.

I've just started using my new D60 and notice that photographs are shown as 300dpi, which seems to prevent them being enlarged once they are on the site.

Help please"



The dots-per-inch (dpi) determines the amount of pixel information packed into the area destined to be printed. A resolution of 300 dpi is only suitable for quality printing. Getting that sort of resolution requires a large size file assuming that its not going to be a print the size of a postage stamp.

The size of images on the screen is determined by the number of pixels (dots) in the width and height, and this, in conjuction with the JPEG (compression) quality determines the physical size of the file. But the dpi value has no effect on the image as it appears on the screen or its size on the web.

The Photography Cafe, like every public website, has to place restrictions on the size of the files that are uploaded. So it is for that reason we have to impose a limit. We also restrict the length of the sides (measured in pixels) so that most people will be able to view the whole picture without scrolling. A high quality image of (say) 800 by 800 pixels would probably create a file that is way too big, so you have to apply JPEG compression to keep that file size down. It is amazing how much compression an image can take without showing a discernable loss of quality.

Check your editing software for image saving options and look (specifically) for a "Save for Web" option. In Photoshop CS I find that, when you do a "Save As," a JPEG compression of "7" works nearly every time.