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Author Topic: Is 360 PPI for Epson really necessary?  (Read 11490 times)

nanjeca

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Is 360 PPI for Epson really necessary?
« on: January 26, 2009, 11:47:07 am »

Hi all

I recently read somewhere (can’t remember where – doesn’t matter) that when using Epson printers, one should always format the image file being sent such that it has a resolution of 360 PPI (or a multiple thereof, 720, 1440, etc.). I seem to recall in the Camera to Print videos, that the suggestion for all (non-specific to printer) was 240 was sufficient and 300 was the max you should need. I do understand the difference between DPI and PPI. The statements centre around whether one should use an interpolation method to get to 360PPI in the actual print size desired (using Genuine Fractals, PS-CS4 or Lightroom’s bicubic methods or, if one didn’t, then the printer would use a less capable algorithm to do the same in order to print.

I am a member of the Epson Large Format Yahoo group and I posed a similar question to their members. The consensus response from them was that it DID matter and ideally you should re-set PPI accordingly. However, then some brought the discussion down to the biology of human vision, etc.

All I would like to ask is, does it make any real, noticable difference to the normal perception that one would have of a large format print, say 24 x 36 or is it all theoretical and doesn’t really matter.

My setup for those that may ask is a Vista x64 based PC driving a 7880 Epson using Lightroom and Photoshop CS4 – RAM and drive space are not issues.

Thanks in advance

mike

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Lisa Nikodym

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Is 360 PPI for Epson really necessary?
« Reply #1 on: January 26, 2009, 12:05:46 pm »

This question comes up every so often here.  I can tell you what was true several years ago; I have no idea whether Epson has made any changes to make this obsolete in the meantime, but this is what I found then...

I did my own test, taking a small piece of an image and rezzing it to 180 ppi, 240 ppi, and 360 ppi, and leaving it at its native resolution of about 210 ppi, and printed it each way on my Epson printer (which I believe was probably a 2200 at the time, though it might possibly have been my previous 1520).  I found that the worst one was 210 ppi.  180 ppi was slightly better, and 240 & 360 were slightly better yet, but 240 & 360 were indistinguishable to the naked eye.  However, the differences between the best and the worst were very small; you'd have to be studying them carefully to see the difference.  A casual observer would never notice the difference.

I interpreted this to mean that the printer's internal interpolation was worse than Photoshop's, and it did indeed help to have PS interpolate to a resolution the printer wouldn't need to further interpolate (180, 240 or 360).

It would be easy to do a similar experiment with your current printer to see if you get the same results now.

Lisa
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JeffKohn

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Is 360 PPI for Epson really necessary?
« Reply #2 on: January 26, 2009, 12:20:17 pm »

I still think there's benefit (even if very small) to interpolating to ppi that's divisible with the print driver's native resolution. Epson print drivers use 720ppi internally for desktop models (13" and smaller), and 360ppi for larger models. That means if you feed the print driver anything else,  your image will get interpolated to those numbers. In the past, print drivers have use s simple nearest neighbor alogorithm which is far from optimal. It may or may not be true that today's printers use better algorithms, although short of talking to the dev who writes the drivers there's really no way to be sure. But even if the drivers have gotten better at interpolating I still think there's a valid reason for doing the interpolation myself: I don't want the file being interpolated after I've already applied print sharpening: I would rather interpolate and then sharpen.

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Jeff Kohn
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sesshin

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Is 360 PPI for Epson really necessary?
« Reply #3 on: January 26, 2009, 01:07:34 pm »

I've done similar tests on my Epson 9880, printing an image at equal size at 180, 240, 300, 360 and 720 ppi. I found that 360 is sharper than 300 especially along straight lines. I couldn't tell a difference between 360 and 720 though so I use 360. Epson recommends using 720 on vector images  with 'Finest Detail' turned on, so that doesn't really apply to photographs.

Since I've started using LIghtroom though all of this is moot. I just leave my file at it's original ppi and have LR interpolate to the desired print size with output sharpening applied. I've been using Jeff's guidelines in the video. Correct me if I'm wrong but if the ppi falls under 180, interpolate to 240, if it's 200-300 interpolate to 360, and if it's above 300 interpolate to 480. Jeff doesn't mention this but if its 360 I leave it at 360. This process has been producing the sharpest images for me so far.
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Bruce Watson

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Is 360 PPI for Epson really necessary?
« Reply #4 on: January 26, 2009, 02:23:09 pm »

My two cents. The Epson driver seems to take whatever you give it and convert it to either 360 ppi (wide format models) or 720 ppi (desktop models). It uses this "known" base to build it's dither patterns. Why? Because it's easier to build and test the driver software this way, and the code is smaller and less complex.

RIPs like StudioPrint OTOH seem to take what you give them and build dither patterns directly without any conversion to any particular output resolution. They do this even though it makes their algorithms more complex for two reasons. One is image quality, clearly. The other seems to be that they can pull nearly all the processing from the printer into the RIP where they have more code space and more memory space and can therefore run more complex algorithms.

I've done the testing with StudioPrint. Scanned the same film four times (same print size, but four different output resolutions (360, 300, 240, 180)) I did it this way to avoid up and/or down rez-ing the file in photoshop. Then printed the four without any processing, put the four prints up on the wall side-by-side under the same lights.

At "normal viewing distances" (distance from print about the diagonal measure of the print) the 180 print was pretty bad. The 240 print was pretty good. The 300 print was a little better. I couldn't see any improvement in going to 360. At close distance (about 30 cm / 12 inches) the 180 print was garbage. The 240 print was OK, the 300 print was nice, and I could just see the improvement in 360.

But none of the prints showed any "jaggies" or other oddball artifacts. They were all nice and smooth, even the 180 one, but the lower resolution prints just lacked detail.

When you do this same test with the Epson driver, most people see some artifacting (including jaggies) from output resolutions that don't match the native resolutions of the drivers.

And it's all easy enough to test. No one needs to take anyone's word for anything. Nor should they.
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Bruce Watson
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bwana

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Is 360 PPI for Epson really necessary?
« Reply #5 on: February 06, 2009, 11:24:30 am »

ok, so what do you do when you want to print to a specific size? For example, setting my image to 360 dpi makes it 5 inches tall. I would like a taller image, 7 inches. That results in a lower dpi, no?
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Wayne Fox

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Is 360 PPI for Epson really necessary?
« Reply #6 on: February 07, 2009, 02:48:02 pm »

Quote from: bwana
ok, so what do you do when you want to print to a specific size? For example, setting my image to 360 dpi makes it 5 inches tall. I would like a taller image, 7 inches. That results in a lower dpi, no?

for prints that small, just print it and set the final size in the driver.  Complete waste of time to interpolate to a "5x7" at "360" dpi.  
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Victor Glass

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Is 360 PPI for Epson really necessary?
« Reply #7 on: February 21, 2009, 05:54:04 pm »

Quote from: bwana
ok, so what do you do when you want to print to a specific size? For example, setting my image to 360 dpi makes it 5 inches tall. I would like a taller image, 7 inches. That results in a lower dpi, no?

Since I am giving a show and had to do 50 prints of various dimensions I looked into this issue and I now do this:

In photoshop I either set the dpi to 180 or 360 with "resample image" OFF. If the print is going to be small or medium sized I use 360; if it is going to be large I use 180. I then set "resample image" to "ON" and increase/decrease the physical dimensions of the print to the numbers I want  (I may do this incrementally). If the resulting dimensions are not exactly what I want (often) I cropped the print using the same dpi (360 or 180). I am only talking about fractions of an inch here for most part, e.g 20.013 -> 20). This sounds like a lot of steps, but I produce photographic art and I am not doing volume. Also, some people use Qimage, which does the work for you. I looked at a trial of Qimage, but decided I wanted to drive the software instead of the software driving me. By the way, for many large prints 180 dpi works well   .
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