Image Resolution. To Convert or Not To Convert

[TMR Design]

Hello,

I still get confused by the whole image resolution issue and when to convert or not.
I use an A620 which shoots at 180dpi. When I submit photos or catalog pics for output I am asked for 300dpi images. I make the conversion but don't see the need or benefit. How can converting to 300dpi after the fact accomplish anything? When I print photos myself at home should I be making a conversion?
Also, if I am going to upload pics here or other sites, do I keep the images at 180dpi or convert to 72dpi since that is what we view on screen?

Can someone clarify this mystery for me?

[Jon]

The "dpi" stored in the picture is meaningless except to certain output devices. The places you submit to may either be using printers that actually do use that value, or they may be trying to stipulate that the photo be able to produce e.g. an 8x10 print at 300 dpi (or 3000x2400 pixels). For here, the dpi value doesn't matter.

[TMR Design]

Thanks Jon,

So does this mean that I just take the images from the camera and do whatever I need/want to and edit for Document size as opposed to pixels? Obviously if I crop or resize to 800 x 600 then the document size changes as resolution is altered, but if I make it 10" x 7.5" then no matter what resolution it is still those dimensions.

Whenever I am creating graphics for the web specifically I always work at 72dpi and do everything in pixels. Does this make sense or should I be doing something different?

[Jon]

Depends on your output device. Web servers use pixels for positioning (or percent of the available screen real estate). Most ink-jet printers will resize on-the-fly if you want; the individual application may also override dpi setting to produce a desired print size, or vice versa.

[ssd]

Thanks Jon,

So does this mean that I just take the images from the camera and do whatever I need/want to and edit for Document size as opposed to pixels? Obviously if I crop or resize to 800 x 600 then the document size changes as resolution is altered, but if I make it 10" x 7.5" then no matter what resolution it is still those dimensions.

Whenever I am creating graphics for the web specifically I always work at 72dpi and do everything in pixels. Does this make sense or should I be doing something different?

In general, what really matters is the total number of pixels along the length and the breadth. DPI is a property used for printing through a printer (not for viewing in a moniter or television).... it is the number of ink droplets per inch that the printer would spray on paper. Genearally 300 dpi is very good.... anything above 200 dpi is workable. Human eyes are unlikely to differenciate dpi's above 350.