RE: [APML] OT: Photoshop lines per inch and Epson 1270

[Jerry Lodriguss <jerry@astropix.com>]

 > After scanning and enhancement, when I run the printing resize wizard in
 > Photoshop I am asked how many lines per inch I want the finished file to
 > have.  I always guess at something fairly high because I have no idea of
 > the maximum lpi the Epson 1270 can handle.
 >
 > Does anyone know what the proper lines per inch for max resolution out of
 > the 1270 should be?
 >
 > Also, I always print at 1440 dpi, which is amazingly slow.  Do those who
 > use the 1270 see differences between printing at 1440 dpi and 720 dpi for
 > astrophotos?


Hi Alan,

First, note that dots per inch, lines per inch, and pixels per inch are NOT 
the same thing.

If I were you, I would just use the Image > Image Size command instead of 
the resize wizard. Talking about dpi and ppi is confusing enough without 
getting into lpi.

In the Image size command, just make sure you have Resample Image checked 
on and bicubic selected. Change the Document Size to the width and height 
you want the print to be, and then use the following information to set the 
resolution in pixels per inch.

If you un-check the "resample image" box, and put in the width and height, 
the resolution will change to give you the true native resolution of the 
original file. You will then have an idea of how big you can resample it 
upwards if necessary. Usually, you can get away with a resampling of about 
2x the original file size.

Epson suggests using 240 pixels per inch for high quality printing on good 
photographic papers with their photographic inkjet printers. You may be 
able to get away with as little as 150 pixels per inch, depending on how 
critical you are. Some people use 300 PPI or even 360 PPI. But this means 
that you have to have that much true optical resolution in your original. 
Using interpolation on a small file to reach these high resolutions will 
not provide the highest quality output.

Lets take an example of a sharp fine-grained 35mm transparency original 
scanned at 2700 pixels per inch of true optical resolution. This produces a 
2700 x 4050 pixel file that is 31.3mb.

If we want to print this image with a print size of 10 x 15 inches on a 
photographic quality inkjet that prints with 2800 dots per inch, we would 
not multiply 10 inches times 2880 dots and think that we needed 28,800 
pixels by 43,200 pixels to make a print. Remember, dots do not equal pixels 
in this context.

Instead, knowing that 300 pixels per inch will produce excellent output 
with these printers, we would divide the true optical resolution of the 
original file by 300 pixels per inch on the short side of the print and see 
that we had enough true resolution to output 9 inches (2700 PPI / 300 PPI). 
We could output 10 inches on the short side at 270 PPI, and this would 
probably also produce an excellent print.

I have some more info at:

http://www.astropix.com/PFA/SAMPLE5/SAMPLE5.HTM

Depending on the image, you should also apply an unsharp mask before 
printing, but with astro images it is easy to aggravate the noise if you 
sharpen it too much.

Jerry

Photoshop for Astrophotographers - http://www.astropix.com/PFA/PFA.HTM











_______________________________________________
Astro-Photo mailing list
Astro-Photo@seds.org
http://seds.org/mailman/listinfo/astro-photo