I don't know the math relationship, I would start my tests at 175ppi and not exceed 300ppi...will likely depend on subject matter.

I know someone's going to bark at me to read other posts, so before you do, know that I have. Most of them deal with people not understanding resolution, resampling, and rescaling.

I have a simple question which (in my perfect little world) should -- i hope -- have a simple answer.

If i'm outputting to an imagesetter, I ask my print vendor what line screen they're printing at, multiply it by 2, add a little extra, and VIOLA, I know what to set my Photoshop resolution at:

2 x LPI + a little extra = PPI

2 x 133LPI + a little extra = 300PPI

However, what about if I'm outputting to an inkjet printer? It doesn't use halftone screens, so I have no idea what I need to res-up to. There's gotta be a threshold where all I'm doing is adding excessive pixel data without a visible increase in image clarity.

Technically, I'd be outputting to an Epson 1280 or 2200. I imagine the answer will have something to do with the DPI capabilities of the printer itself, but I need to know the mathematical relationship between the DPI of the printer and the PPI of my Photoshop doc.

I teach this stuff, so, please, tech jargon is welcomed.

ramón_g_castañeda

I prefer 360 ppi, simply because my Epson 2200 prints at 2880 dpi (360, 720, 1440, 2880 are easiest to convert).

However, if the image is anywhere around 250 ppi or more, I don't bother to up-sample. I just let the printer handle it.

It also depends on Viewing Distance...16ppi may also be good.

Cool, Ramón. That's about what I figured.

G Ballard has some pretty good advice, too, I suppose: just test it out.

So, as a general rule of thumb, anything lower than about 175ppi is going to be noticeably pixelated, and anything over about 300 is going to be overkill?

ramón_g_castañeda

What G says. It does depend on viewing distance.

As far as over 360 ppi being overkill, if for some reason I had an image that was over 360 ppi, I certainly wouldn't down-sample it. But there is no reason to up-sample an image beyond 360 ppi for output on the Epson 2200.

With the new Bicubic Softer capabilities of Photoshop 8, I'm finding myself up-sampling old images with more confidence than before. I guess it depends on how the up-sampled image looks on the screen.

G -- Smartass

It's not being used to print billboard tiles heheh

I'm using it to print pages for my design / layout portfolio, so a good mix of text, line art, and photography. Viewable at normal reading distances.

Ramón -- agreed. The shots of my stuff were taken with an 11-megapixel Nikon, so they've got plenty of pixel data, but I'm going to be blowing them up to fit 13 x 19 pages, so I think I'm going to have to do a bit of upsampling.

jeff_schewe

If, and this is a big if, you prepare your files correctly in terms of sharpening, you can indeed tell the differences between various output resolutions. Determing the EXACT amount of output rez you need is dependent upon the native resolution of your file-uprezing will not help output, your image type-strong high frequency texture will use higher resolution to better keep detail, and you intended viewing distance-which is generally 2X the diagonal of your print size.

Also, it's useful to send images to the printer that are exact divisibles of the print head resolution such as:
180ppi,
240ppi,
288ppi,
360ppi,
480ppi.

The resolution you need also depends on your media. Matte or watercolor paper can not hold the detail of glossy or semigloass coated papers. Printing small prints (5x7) on glossy with proper sharpening, you can tell the difference between 240, 360 & 480ppi on a high quality coated paper printed out at 2880dpi on an Epson 2200. You will need to sharpen matte output more/different than glossy output.

Again, you need to test out YOUR images at the various resolutions and YOUR images to determine of the higher resolution of the images and the printer is worth the larger files and longer print times.

On the other hand, I often use 180ppi @ 720dpi for 30" x 40" prints on my 9600 on watercolor because the high rez on watercolor paper is fine-unless you look at the print from 6 inches away. . .

venicia_l_2

Mister eaves,

You can prepare your files at 300 ppi for Epson inkjets and not worry about other resolutions unless you really want to split hairs.

I don't know why this topic gets some workers so passionate, but there have been real flame wars about this. One "authority" claimed that 260 ppi was the maximum EVER needed for 1270s, 1280s and the 2200 and that no further improvement could be seen using higher image resolution. In fact, he insisted, 240 ppi was generally all the Epsons could utilize.

I can see improved quality at 360 over 300, but it's because I know which prints are which. I have NEVER been able to get anyone else to distinguish between prints made at 360 vs 300. So I use 300 most of the time. 360 takes much longer to print. 300 ALWAYS beats lower input in my prints, so I don't go lower.

As far as resolution for press, there is nothing to be gained by adding any extra resolution to the 2x lpi formula. Since most commercial work is 150 lpi, 300 ppi is all you need to prepare and that covers the inkjet also. Very convenient. In fact most imagesetters can produce the same quality at 175 lpi from 300 ppi images.

VL

"As far as resolution for press, there is nothing to be gained by adding any extra resolution to the 2x lpi formula."

Every printer I've ever talked to has asked me to include a bit more pixel data than actually needed. I've always chalked this up to a few variables:

1) In case a client wants to make a slight enlargment at the last minute, the is pixel data is there to use as a buffer.

2) In case a photo needs to be moved to a different position and needs to have room for a bleed, you can enlarge it slightly and, again, use the extra pixel data to do so.

3) A LITTLE bit extra never hurt anyone... especially with the fast computers in production houses these days. I mean, I'm not advocating scanning at 500ppi for 133lpi or anything, but ... I've always got a few extra bucks in my wallet just in case.

* shrug*

Splitting hairs, I suppose.

Thanks for the advice on my ink-jet question. You guys are really helping.