difference between pixel dimensions and resolution?

[obliex]

Hi,

I am using photoshop and realise that they seem to be some difference between poxel dimensions and resolution.when send my image for printing, the printing company always say that they need at least 300dpi, is this resolution. But when the image is taken by digital camera, i realise it is calculate by pixel dimensions.

Please help. what should be the actual quality we should be looking at for printing.

Thanks in advance.

 

[MarcusStringer]

I think if you have you camera on the highest setting it will 72dpi, they should be saying ppi (pixels per inch) instead of dpi (dots per inch) which is old school talk before digital came along, but everyone still refers to it as dpi.

Now I think all digital cameras take shots at 72dpi resolution but depending on the quality setting depends on the size of the image, A3 size which would be at 72 dpi (xxxpixels by xxxpixels, not sure of exact vaule). when you reduce that A3 size image down to a standard photo size, then the image dpi will increase to 300 odd dpi which is what you want for printing. once reduce the pixels dimensions will also change

hope that answered your question

Marcus

http://www.midlandtypesetters.com.au

 

[kiddpete]

The camera has a stated number of pixels at a given quality level. This doesn't have much to do with dpi. It is simply the amount of resolution that the camera has to represent the picture it is capturing. As resolution increases, the amount of detail captured increases.

DPI refers to how an image is displayed on a device, as well as the capacity of the device. There is little to no relationship between an image's dpi and a printer's dpi. A rule of thumb is that an image should be at 150-200 dpi for good quality printing. The printer may print at, for example, 1440 dpi, but that does not mean the image has to have that dpi.

 

[blueark]

Let's say your image is 1800x1200 pixels.

At 300dpi, every 300 pixels is one inch. Therefore, the above image at 300dpi will be 6 x 4 inches. At 100dpi, it will be bigger (18 x 12 inches), but each pixel will be 9 times larger (3 across x 3 down). If you go too low in resolution, the pixels will become too obvious. However, as the pixels are getting bigger, so will your image.

The trick is to balance the number of pixels per inch with the capabilities of the printer. 300dpi is generally considered standard, and most printers will ask for this figure.

It's calculated against something called the line frequency, and in general, the resolution has to be sufficient to allow each point in the line to be unique. The details can get quite technical, and the actual dpi required can vary drastically depending on the image. However, 300dpi is usually safe, and you can often get away with less.

Anyway, to get to the point, open your image in Photoshop, go to Image > Image Size..., turn off "Resample Image", and change the resolution to 300dpi. You can see at a glance what the maximum size your image should be, theoretically. You can push it a little bigger, and there shouldn't be any problem reducing it in size.