How many PPI do you send to your printer?

[Tim_S]

I went to the NAPP Photoshop World conference in San Diego. (Briefest summary, it was worth the expense, but I won't go again).

Anyway, I took a class there where the instructor said that for optimal printing to an inkjet you should send a file with a ppi that equals 1/3 the dpi of the printer; ie. for an Epson with 1440 dpi capability you should send a file with a resolution of 480 ppi.

Now, I had always heard that no inkjet printer had a real output of more than about 300 ppi (I've heard 240, 320 and 360 ppi for various Epson printers). The 1440 dpi number is for the spacing of the component single color dots that make up a "pixel" of continuous tone color. In a short discussion after class the instructor confirmed he meant that to apply to all inkjet printers, though he allowed it didn't seem to be true for older inkjets.

Well, I felt I needed to test that. The best way I could think of to isolate the printer resolution was to create a digital file at different resolutions and print them. What I made was something that looks a bit like a UPC barcode. There are groups of five lines separated by a fixed number of pixels of space. All lines are 1 pixel wide, and the groups start with 1 pixel between the lines, and went up to 8 pixels between the lines. The pictures only show the first three groups.

I made sets of lines that ran both horizontally and vertically. This was done for 300, 400 and 500 ppi. I resized these by doubling the pixel resolution without resampling in Photoshop to get 600, 800 and 1000 ppi versions.

I used an Epson C80 printer and Epson Photo paper (the comment about older printer kinda leaves out my true photo printer; an EX). I printed in 1440 Photo (1440 x 720 dpi) mode.
Note, that the color was equal amounts of CMY, so multiple heads were involved, not just the black head.

I was surprised to see that, with a loupe, you can make out lines and spaces in the horizontal single pixel spaced lines up to 600 ppi. The vertical lines (remember Epson's dpi is 720 in this direction) could all be made out at 400 ppi, and in only one line was the space filled at 500 ppi.

In the horizontal lines, you can make out some lines even at 800 ppi. The other thing that surprised me was the variability of the single pixel lines at all resolutions. There seems to be rather a lot of variability in width.

Wow, this is getting way too long. What resolution files do you send to your printer? Do ppi s higher than 300 really make a difference?

Results:

[Tim_S]

The vertical lines:

[BigAl]

You may want to check out Norman Koren's comments on this (especially the bit "How many pixels do you need").

[Ed_L]

Tim,

I've found that members of my family (that's who I do printing for) cannot see a difference between an image printed from a 150 ppi file and a 300 ppi file. Personally I don't think it's worth printing at anything higher than 240, but I'm sure there's room for debate. I try to keep my file sizes small, without sacrificing too much in the way of quality.

Big Al,

Thanks for a *very* informative link. There's a lot of good info there, and it deserves a spot on my favorites.

Ed

[Tim_S]

Thanks Al, I actually looked at that site before I tried my little experiments. The data there show that with a 1270 there was more measurable resolution in the print when a 1000dpi image was sent, than when lower dpi images were used. While Norman's experiments are valid and probably correct, I'm not sure they are a direct answer to my question.

I worry a little about his repeated "Picture Window Pro resamples the image using bicubic interpolation before sending it to the printer" statement, since if you resample a single pixel wide black line to a higher resolution you don't get a black line, but a grey line and a black one taking up the space that should be occupied by a solid black line. It is not clear if his varying magnifications are created with resampling. That is why I build individual files of each resolution, except for situations where I could resample without any form of interpolation.

My original problem was the years fo advice that sending more than 300ppi data to the printer was useless, was challenged by an instructor at Photoshop world. This data seems to back his statement that the printer can actually produce more detail using this higher resolution data.

With a photograph I'm with Ed. Anything over about 240 I can't tell the difference on the Photo EX. A couple quick tests with the C80 however seem to give better detail when sent 400dpi pictures than the same file at lower resolution. This may be partly due to the C80's poorer color blending since it is only a 4 color printer (but dang it is fast).

--tks

[thomasgeorge]

Tim, while with a loupe you can see a difference, taking into account the twin facts that the human eye can only grab a limited amount of information and that most folks tend to view prints from around 8-12 inches or so in distance, the differences which are evident between a 300 or 500 dpi print with "up close and personal" inspection, tend to wither to unnoticable under normal viewing conditions. Just speaking for myself, I send files to the printer at 300 and have had no complaints from customers. Again, since the purpose is, in the majority of cases anyhow, perceptual enjoyment and not minute inspection, files larger than 300 would seem to do little other than increase the amount of ink used and possibly give problems with ink over saturation, smearing and so on....just some thoughts...good luck....Tom

[john_opitz]

Here's an article on this subject. It's from Mr. Margulis' book P.P.S.6.

Chapter 14 from Dan Margulis

It's in pdf. format.

The reason why I'm not commenting on this subject is because I agree with Mr. Margulis on this subject. And also with Mr. thomasgeorge

[ghoffman]

Scan Tips also contains some good info about how many PPI you should send to your printer.

Gene

[Guest]

Originally posted by Tim_S
The vertical lines:

So Tim, what is the bottom line? With my cheap HP 810c what should I print at?

[Tim_S]

I'm not sure there is a direct simple answer. If you send 300ppi it will always look fine. Is there a real difference at other resolutions?

I've sent 240 ppi to my EpsonPhoto EX and it looked great. I can see higher resolution off my C80 printing at 480 ppi, but at normal viewing distances I can't tell a difference.

300 ppi is always safe. If might be a little more, or a little less than optimal, but it is a good bet it will look fine.

--tks

[john_opitz]

All that stuff depends are the image itself. Depends on what your outputing to,as well. When I print to the Durst Lambda. The res. for the Lambda is 200/400 ppi. You can even go low as 150 ppi.

I did a retouch on an 11 x 14 org. print. The person wanted to output to 16 x 20. So it was scanned at 400. I should say it was scanned for output 16 x 20 size......400 dpi res. from the scanner(flatbed). I did the retouching on it.......Leaving it at that size and dpi. For output to the Lambda. Inkjets and cmyk printing are different. Wasn't bad. For a scanned 11 x 14 print from 1969.