PeterF said:
Hi guys
I am on a speed learning mission, trying to understand how large an
image I need to create in Photoshop to print to A3+ with a format of 13
by 44 inches.
My desire is to print at about 400 DPI, in part because I keep reading
that this is pretty much the minimal requirement for photo quality
output.
400PPI (Pixels per inch) is probably a bit of overkill for an inkjet
image, especially for a larger image. Keeping in mind he larger the
image, the further away the viewer will be to look at it. Drugstore
style prints (from a wet lab) usually resolve to about 200 dpi, and
those are usually small and viewed up close.
But when I read the specifications for the printers I consider for
purchase, I am unsure as to what these specifications mean for my
design:
Epson R1800 and R2400 say they print 5760 x 1440 optimized dpi
Epson Stylus Pro 4000 suggests:
· Fast printing at 720 x 360 dpi
· Quality printing at 720 x 720 dpi
· Photo quality printing at 1440 x 720 dpi
Some of this is just hype, but some is about understanding what these
numbers mean. The numbers you see are the possible positioning on any
one dot on the paper. Any ONE dot. That is one color of ink only. In
order to create the hundreds of thousands of colors you see on a print,
the dots have to resolve small enough that you do not see individual
dots, but instead a group of dots that together give the illusion of a
blended color. The matrix necessary to do this is usually at least 16
dots (4 x 4) or so. The reason I can't pin this down exactly, besides
that it differs depending upon the printer and the color and the number
of inks used, is because most color inkjet printers use a system which
is constantly adjusting dot colors and relationships per line slowly
adjusting to subtle blends, unlike offset printing, which does use an
exact matrix on dots.
So, other than the exact ink colors coming out of the cartridges, all
other colors are mixes of colors by placing different colored dots next
to one another. In the case of Epson printers, depending upon the
vintage of the printer, and the size of the carriage, the software
always rasterizes the image up or down to 360, 720, or 1440 ppi,
regardless of what you feed it. Most Epsons use 720 or 1440 today.
However, what yo need to know is that the visible differences between
supplying a 300 ppi, 360, 400 and even 720 ppi source file becomes
increasingly diminished, and the advantage is lost when considering the
size of the file, amount of hard drive space, spool space, time involved
in rasterizing the image, and working with in in something like photoshop.
So, my recommendation , and my personal use, is to usually feed the
printer images at somewhere around 300 ppi or even less from large
images (over 12" wide) and for smaller images 360 to 400 max. After
that it is really a toss up as to what the advantage is, although some
very high contrast images with sharp details on contrasting colors MAY
benefit for up to 720 ppi is you are really looking at the thing with a
loupe.
So, that's about source file resolution and rasterizing, however there
is a second matter, that of printing resolution... or how many dots per
inch maximum you want the printer to produce.
The smaller the dot the printer produces (usually in picolitres), and
the lower the number of ink colors (especially with four color CMYK),
the more important the printer output resolution is. However, having
said that my experience has been that over 1440 dpi becomes difficult to
notice, and slows the printer down considerably. For draft work I use
360 or 720 dpi, for photographic work, final version on smaller images
(less than 11" wide) I go 1440 if the paper is capable of high
resolution and low dot gain. Otherwise, I'm back at 720 dpi again (and
that's for printers with only 4 color inks, six color or more makes it
even less important, because they blend with less trouble, usually use
higher dot sizes, etc.
Lastly, there is the issue of what part of your personal arsenal does
the bast job of upsampling your image. For most people, Photoshop does
the best job of upsampling. This means taking a lower resolution image
from, say a digital camera, and bringing to the printer output
dimensions in the ppi resolution you want. For example, let's say you
have a 4 megapixel image about 2300 x 1730 ppi. Left alone, without
upsampling, that image will make a 300 dpi image at printer output of
about 7.7" x 5.75", so if you need a larger image output from the
printer, say about 14.5" x 11" that same image is now only about 160
ppi. So, you probably want to upsample it to about 240-300 ppi or even
more (360?? ppi) and if Photoshop is the best method to do so, you would
use it to do the upsampling. But you may also have a really good
printer utility which may do a better upsampling, and therefore you may
prefer to have it upsample the resolution. Keep in mind that all of the
methods for upsampling the image will interpolate or create/manufacture
pixels based upon some knowledge of surrounding pixels in the image. In
some cases you might even find that not upsampling and just allowing the
printer rasterizer to print it as is will supply the better result.
It takes some experimentation to determine which method gives the result
you best like. Also, almost all images after upsampling or when taken
from a digital or scanned image need some unsharp masking to reestablish
the lost resolution due to the noise suppression and sampling
algorithms, but it needs to be used with some judgment.
