ivan said:
Hello All, Do you know how I might find out at what resolution (DPI) an
ink-jet printer (epson 860) is *actually* printing? Any replies gratefully
received.
In common with all Epson desktop inkjet printers, your Epson Stylus
Color 860 printer will always print at 720ppi, irrespective of what you
send it. The first step in the printer rendering process is to resample
everything to 720ppi if necessary.
The Epson driver is capable of resolving the full resolution if it is
present in the image with sufficient contrast. However it will
dynamically adjust the actual resolution to achieve the best tonal
quality with the inks available. So, if the exact colour you want in a
certain pixel cannot be achieved, the error between what is required and
what is available from the inks will be distributed to the 4 of the 8
nearest neighbouring pixels that have not yet been printed. Thus, if
high contrast detail is present, it will be printed at full resolution,
but if it is low contrast then the error of any given pixel will be
spread over several pixels, in effect trading resolution for exact
colour rendition.
Being limited to 4 colours with the SC860 means that this occurs more
than it would with 6, 7, or 8 colour printers, so more resolution must
be traded for colour precision, but it is impossible to say with
accuracy what the actual resolution on any part of the image *actually*
is - so there is no fixed answer to your question. You can, of course,
limit the actual resolution in the image you send the printer, thus
giving the printer more tonal precision in individual pixels. For
example 360pp gives 4 times as many ink potential drops, and thus 4x as
many reproducible colours, per pixel than 720ppi, whilst 240ppi will
produce 9 times as many. An unaided human eye can only resolve about
250ppi on a printed page, so limiting the resolution in this way is
almost imperceptible on the best quality paper and even more can be
traded on poorer paper. If you have the resolution in the original
image, it is generally better to let the printer driver trade the
resolution than restrict it yourself in this way, because the driver
will do it dynamically across the image - yielding best resolution where
it exists, which means your prints can stand closer examination.
However, because the printer driver always resamples to 720ppi in the
first place, you should always use an integer division of 720ppi to
avoid aliasing, which can become obvious depending on the content of
your image. For example, some text strokes can appear thicker than
others or, in images, bricks or windows in buildings or paving can
appear uneven or have a coarse pattern running through them even though
the original image is perfectly regular. For Epson printers this means
that the magic numbers are 720ppi, 360ppi, 240ppi and 180ppi. For
resolutions below 240ppi it is recommended to select the
