Wumply pm'd me regarding some questions about Printers and DPI as well as Interpolation. I thought it noteworthy enough to post here for the benefit of other users:


...my questions are going below the surface with detail, so please answer only what you have time for and if you can refer me to a site that addresses this specific area, it would be wonderful.

I know that when an image is interpolated with software, pixels are added to smooth things out--by an algorithm that looks at surrounding pixels, measures their color and assigns a particular color pixel or pixels to fill in, so edges are not jagged.

But when a printer is rated at 2400 x 1200 dpi, what is occurring--are more dots added than sthe printer is optically designed to lay down. And is this considered interpolation. Does a printer have a basic mechanical (non-interpolated) dpi like 300 oer 600?

Also, if more dots are added the printer must slow down...I understand that. But are the colors of the added dots figured out same as in software interpolation?

And are the dots made smaller if one sets the printer for an increased resolution - I mean, would they not have to be to get more dots in the same page size? Can a printer then print dots of different sizes?
What I wrote below:

Here are some articles to help explain this:

http://www.ransen.com/Articles/DPI/Default.htm
The article above just gives a decent rundown of DPI for images. Good background info.

http://aroundcny.com/technofile/texts/tec122103.html
That article debunks the DPI myth. IN fact you are correct a 1200 DPI is really only 300 DPI X 4 (the colored ink and the black ink).

Below is a good article on interpolation:
http://www.megapixel.net/cgi-bin/fs_...rpolation.html

It shows what it is using real examples.

And I believe you are correct, as the DPI increases, the dots actually shrink giving the image a clear, and smooth look. I mean you cannot have 300X600DPI and 2400X1200DPI on the same image and it look the same, and the dots be the same size. I believe they actually shrink in size to accommodate the larger number of dots.


And to add further to that:

Now let's talk about DPI. DPI only refers to the printer. Every pixel output is made up of different coloured inks (usually 4 or 6 colours, depending on your printer). Because of the small number of colours, the printer needs to be able to mix these inks to make up all the colours of the image. So each pixel of the image is created by a series of tiny dots (you could think of them as sub-pixels). Generally, the higher the DPI, the better the tonality of the image, colours should look better and blends between colours should be smoother. You'll also use more ink and the print job will be slower. You might want to try setting your printer to a lower DPI to save ink and speed up the job, see if you notice any difference in quality. The lowest setting where you don't see any loss in quality should be the best one to use.

So a 1200 dpi printer uses 1200 dots of ink in every inch to make up the colours. If you were printing a 300 PPI image, then every pixel would be made up of 16 smaller ink dots (1200 DPI x 1200 DPI / 300 PPI x 300 PPI). A lower DPI would have fewer ink dots making up each pixel, which would make the colour look worse. A higher DPI would have more ink dots for each pixel and should give more accurate colour (especially under close examination).


http://www.tildefrugal.net/photo/dpi.html