Below is a sample patch strip; it's the left portion of the 240 ppi
The strips were printed with auto cut disabled, and the paper manually
repositioned for each document. Printing was performed through PS7's
Print with Preview, using Bill Atkinson's 9600 PLU1 profile. The
printer driver was set up as per his instructions for that profile. A
curve was applied to lighten the shadows somewhat (hence the tonal disparity
between the full view and the crop). Resampling and sharpening was
done in 16 bits, all other work in 8 bits (text, strip creation, printing).
Once done, I left the grid to dry overnight. The next day I took a closer
look at the patch grid. One thing was immediately obvious:
the level of detail in the image
doesn't noticably affect hue or tone! This is something I had personally
been somewhat worried about, and it's comforting
to know the gamut doesn't change with the spatial content. Next, I did
a cursory overview, eyeballing definition and sense of texture. There
are definitely noticable differences, though they are subtle. On the
340 ppi strip, the 0.5/125%/0 patch looks best; on the 240 ppi strip the
0.4/125%/0 patch looks best. They are hard to compare, though, because they're phsycally at different ends of
The next step was to take a 10x loupe to the patches to see where the
resolution starts dropping off. Easier said than done... Frankly,
I can't tell the difference. At one moment, 300 ppi 0.4/125/0 looks
best. Then 340 ppi 0.5/125/0 looks better. Then something else,
and I'd go around in circles. I tried to lock onto extremely fine
detail in the 340 ppi patches and then
look for the
same in the 240 ppi patches. Still there? Does it look softer, worse? Yes... no... maybe...
sigh. Since this was getting nowhere, I held the print up next to
my screen, showing patches at 200%. Now, clearly the 340 ppi image
showed some detail not in the print. Checking the 340 ppi strip against
the image data for 320 ppi, I could still find
unprinted detail. The same was true at
300, 280, 260... and that's just about where it started matching. The
340 ppi print patches show no more detail than what's in the 240 or 260 ppi
image data. (They differ only by 10%, so the difference between the
two image resolutions in terms of actual detail is rather minimal.)
I attempted to make close-up images
to illustrate my observations, but due to lack of consistent lighting (I
used a flashlight for illumination) and print flatness issues, I didn't
manage to make accurate dot pattern magnifications. I'll have to think
about this some more. Meanwhile, I don't think it would be too hard
for the truly suspicious reader to judge for themselves.
So what about the discussions revolving around
printing at even integers, someone who heard that a friend was told by Epson to print 300 ppi, etc?
It makes no difference. The Epson 7600/9600 UC can't resolve 300
ppi. However, there is another aspect here, control over sharpening.
The patches do look different in terms of definition
and sense of texture. How
can this be if they contain the same detail, in fact are virtually identical,
and received the same exact amount of sharpening? E.g., 0.4/125%/0
looks nice and sharp at 300 ppi, but a little undefined at 340 ppi. The
answer is simple: the radius setting in USM is measured in pixels, and represents
a different physical radius on paper
when the ppi changes. And a small change in USM is very noticable
in the print, especially around the area where it goes from perceptually
soft to perceptually sharp; it happens very quickly. Where this happens
depends on the contrast in the original image, the color space, the ink,
the black ink used, and the paper. It may also depend on 1440/2880
Lower resolution input for 1440 dpi prints
What about lower resolution input? What's
the difference between printing images that have detail levels of, say, 150 or 180 ppi, versus 260 ppi? What does
the output look like and is anything lost? To answer this, I prepared additional patch strip documents for 150, 180,
200, and 220 dpi. These were printed as
previously described and placed side-by-side
with the old ones for analysis. At first glance they all look reasonably
good. Then, putting the loupe to the 150
ppi was a real shocker -- pixels! And
lots of them. Square little things. Clearly visible in high-contrast
detail, such as a whitish branch with yellow moss against a dark brown background.
Yikes! Apparently the Epson driver
uses a near-neighbor style resampling algorithm, or at least something that
approximates it for fine high-contrast detail. The softer detail shows
none of this, however. I'm disappointed
in Epson. After discovering this with a 10x loupe I can now see the
telltale signs of it by eyeball up to 200 ppi. With a loupe I can just
barely discern it at 220. Clearly this
is a minimum resolution for the Epson 7600! If you have
less to start with, resample it to a higher resolution using bicubic, stair,
genuine fractals, Qimage pro, VFZoom, or whatever you have on hand. Any
of these will produce a better result than the Epson driver. Just
don't use a low-resolution image as is!
Printing at 2880 dpi
The biggest question remaining at this point was what, if anything, is g
ained by printing at 2880. The Epson
7600 offers an option to print at twice the resolution,
but only along the horizontal axis. Again, I printed patch strips; in the first pass I printed the
180, 240, and 300 ppi strips. One thing was immediately obvious by
just carefully inspecting the prints : 2880
dpi shows better definition. By this I mean that edges are cleaner
and color is smoother, although the latter is only visible through a loupe.
Even the 240 ppi patch looks better at 2880 dpi than at 1440. Curiously,
I couldn't find more detail in the 300 ppi patches than in the 240 ppi ones, it's just better defined. So
the same 240-280 ppi image detail level would seem to apply. However,
even though there is no more detail, 240 produces noticable jaggies while
280-300 is smooth. Seeing this, I've de
cided to do my prints
using 280ppi at 2880 dpi output and use 1440 for drafts and images with 240
ppi or less of image data.
There is a setting in the Epson driver named "finest detail" that's
not entirely clear what it does:
All my previous tests reported here were performed with this setting
disabled. To determine if it adds something, I reprinted the 260 and
300 ppi strips with this box checked, at 2880 dpi. Under a light it
looks identical in terms of tone and hue, so this option doesn't appear
to have any immediate effect on device calibration and profiling. Eyeballing
the 300 ppi prints closely I can perceive no difference. Even under
a loupe, they look the same.
Conclusion and recommendations
- Make sure to print at least 220, preferably 240 ppi with 1440
dpi. If you have less, upsize.
- Any image detail above 260 ppi is lost in 1440 output, and I'd
go so far as to say there is no difference between 240 and 260.
- USM makes a huge difference, and lack of proofing makes it difficult
to master. Clearly this is an area that requires lots of experience.
- USM is easier to control at higher resolutions since it's easier
to make fine adjustments to the radius parameter.
- 2880 has somewhat better definition than 1440 but you want to
feed it at least 280 ppi, preferably 300.
- If you have high-ppi image data, by all means use it. It
won't necessarily show more than 280 ppi even at 2880 dpi though.
Dot Pattern Samples
Dot pattern closeups are in a separate page.