various resolution confusion when printing
Printing slides on my epson 820. The image size is 2710 ppi.
When printed at 720 dpi and 1440 dpi there seems to be no differnce.
When I rescale the image to 300 ppi and print at the above the output is horrible.
Whats the skinny on this?
Do the 720 prints use less ink than the 1440 prints.
What is the best resolution both ppi and dpi to print.
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#1. "RE: various resolution confusion when printing" | In response to Reply # 0dogbyte Registered since 17th Mar 2002Sat 20-Jul-02 04:01 AM
Here's a copy of a reply I made a few weeks ago to a similar question. Not quite the same but probably answers yours queries:
"I prefer to work in metric for image sizes as I find it easier to sort out the positioning on the paper - 297mm by 210 mm with 3mm margins on three sides and 14mm margin on the fourth etc (as it was with my Epson 750). One inch has 254mm. Anyway:
If I were scanning a slide on my IV, max res 2900, actual image size 33.76mm by 22.19mm and I wanted to print at 300ppi without interpolating.
2900 / 300 = 9.667
33.76 * 9.667 = 32.64cm image size along longest axis
22.19 * 9.667 = 21.45cm image size along shortest axis
Likewise if I were wanting to print at 240ppi:
2900 / 240 = 12.083
33.76 * 12.083 = 40.79cm image size along longest axis
22.19 * 12.083 = 26.81cm image size along shortest axis, which fits nicely onto a sheet of A3
I don't enlarge within the scanner software but in Photoshop as I understand its algorrythums (or biorythums or something) to be superior. So in the first case an image is delivered 33.76mm by 22.19mm at 2900ppi which I then resize by reducing the ppi in Photoshop Image>Image Size, constrain proportions resample off (or bicubic if you need it to interpolate). An RGB scan gives a file size of 27.9mb at 8bit per channel or 55.9mb at 12bit per channel. These are higher for a neg as the scannable area is slightly larger than of a mounted slide of course.
For an original image of 5" by 4" to print at 300ppi resized to 10" by 8"
Scan at 600ppi as 600 divided by 300 is of course 2, and multiplying by a factor or 2 along each axis delivers a print of 10" by 8". As I understand it there wouldn't be any point in scanning at a higher res. because you can't discern print differences over 300ppi anyway - and thats with 20/20 vision. The exception might be a tricky image which is going to involve dumping a load of data during editing, in which case you can avoid your histogram in levels looking like a comb with half the teeth missing.
ppi and dpi really are different but unfortunaely the manufacturers use them interchangeably. You can have an image at 150ppi, 240ppi etc, and your printer laying down dots at 1440dpi, 2880dpi etc. 180dpi would be for draft documents, 360dpi for word processing, 720 borderline for photos on inkjet paper, 1440 photo quality, and 2880 for marketing hype (printer reviewers report no difference by the naked eye)."
#2. "Simple printing instructions..." | In response to Reply # 0RRowlett Charter MemberSat 20-Jul-02 03:56 PM
Your 2710 ppi scans should be something like 4000x2700 pixels, more or less. This is plenty to get outstanding prints up to Super B. The simplest way to print is to take this file, change the image size in photoshop to 7.5x10" (or whatever), leaving the "resample image" box unchecked, and then simply print to your Epson. If you look in the dpi box it should read something like 400 dpi or so. That's fine. Print. As long as the dpi value here is >240 dpi your prints will look great. They'll even look good down to 180 dpi. Below that and you should consider image resampling, described in option 2.
Option 2 is to resize and resample your image print to printing. Choose an image size in photoshop and set a dpi setting, typically 240 or 300 dpi, with the "resample image" box checked. Now your final image (e.g. 7.5x10") will be resampled to 2250x3000 pixels at 300 dpi (for example). Print.
When you change image sizes, you should normally leave the "constrain proportions" box checked, and you only need to change one of the dimension (height or width) to resize the image. The other dimension will be adjusted appropriately. BTW, the "dpi" in photoshop are really "ppi", or pixels per inch. A ppi is how many picture elements are printed per inch.
On your Espon printer you can print at either 720, 1440, or 2880 dpi. The "dpi" settings for you printer are actual printer dots. It takes many, many printer dots to print one pixel of a particular color, so this setting really has nothing to do with your image resolution. It does have to do with how accurately and smoothly the printer can render all those pixels in your image. You can get reasonable prints at 720 dpi, but on close inspection you will be able to see faint banding from the print heads. (But you have to get very close.) At 1440 dpi, the prints are essentially smooth, and this is the preferred setting for most high-quality work. The 2880 dpi setting also looks great, but it not really distinguishable from 1440 dpi. And the 2880 dpi setting uses more ink. I never use this setting.
Hope this helps.