resolutions of Epson 1270

C

Charles P Lamb

What is the spatial resolution of the Epson 1270 when printing on photo
glossy paper? What number of density levels can be printed in cyan,
magenta, blue, and grey by the Epson 1270 on photo glossy paper? Has anyone
experimented with this or has this information been published?

Charles P. Lamb
 
K

Kennedy McEwen

Charles P Lamb said:
What is the spatial resolution of the Epson 1270 when printing on photo
glossy paper? What number of density levels can be printed in cyan,
magenta, blue, and grey by the Epson 1270 on photo glossy paper? Has anyone
experimented with this or has this information been published?
Epson have published lots of technical information about the benefits of
their printers in their patents, but it is never clear which patents
dominate or limit the potential of any particular device. Thus, soon
after buying a 1270, when it was introduced, I started a series of
tests, the results of which have been confirmed by others in due course.

The printer operates a stochastic dither process which dynamically
trades spatial resolution and the tonal fidelity on the image for
optimum results. Like all other Epson desktop printers, irrespective of
the dot resolution, the maximum spatial resolution of the image is
defined by the printer driver, which resamples to 720ppi, and this is
just resolvable on Premium Glossy Paper under magnification, the
microporse structure of which restricts lateral diffusion. So 360cy/in,
or about 14cy/mm, is the limiting resolution of the printer - which is
true of all Epson desktop printers irrespective of their advertised
resolution. The advertised resolution states how many ink dots can be
placed per inch, not how many pixels per inch can be rendered.

The 1270 printer itself has six inks, Yellow, Magenta, Cyan, Light
Magenta, Light Cyan and Black, and it can place these inks on a dot
matrix which is 1440dpi x 720dpi. Consequently there can be two dots of
ink placed in each of the highest resolution pixel cells. In addition,
each ink dot can have 3 different sizes, large, medium and small, and
this also changes the amount of ink in each resolution pixel cell.
Combining mixes of light ink, black ink, no ink, and full ink in the 3
sized drops that can be placed in the two available dots per pixel
yields a maximum of 45 shades of Cyan and Magenta, but only 18 shades of
yellow/brown (ignoring the pure black and white combinations, but using
black and white 'dots' to change the average density. Not all of these
shades are actually used however, because many of them are combinations
of light and dark inks that are very close to each other, so perhaps
only half this number are available.

The algorithm used for the ink droplet placement knows what the shade of
each combination of dots is and, for each pixel can work out the
difference between what is placed and what should be placed. This
difference, or error, is then distributed around the 4 of the nearest 8
pixels that have not yet been printed to adjust the colour that they
should be printed at. Thus if there is a large area of colour which is
almost the same, but not accurately represented by the shades available
in the pixel, it can be achieved by more averaging the error out over
many pixels. However if there is fine structure in the image then the
exact colour of each pixel in that structure is less important and the
structure can be represented quite accurately as well.

So the real answer to all of your questions about resolution and number
of colours available is that it really does depend on the image content
- fine details are represented with less colours than large areas and
the printer algorithm dynamically adjusts the resolution and colour
depending on the image content.
 

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