Digital BW, The Print

I understood good practice to be at least always use a clean factor of the
print resolution ie 2880/4=720, 2880/5=576, 2880/6=480, 2880/8=360,
2880/9=320, 2880/10=288.  The 300 simply came about as a result of the old
2x150lpi (as Bob Frost noted in an earlier post).


> From: Steve Gledhill <stephengledhill@...>
> Reply-To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Date: Sat, 17 Sep 2005 13:08:42 -0000
> To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Subject: [Digital BW] 300ppi vs 360ppi
> 
> There has been some discussion of this topic before herein but I guess
> I failed to take real notice of it until the other day when I was
> amazed to see a very rough edge to an angled black line on a print.
> This line appeared as a very smooth edge on my screen.  This effect
> appeared on any high contrast edge that ISN'T parallel to or
> perpendicular to the image edge ­ i.e. it slopes or is angled across
> the image.  The line was actually the edge of some large text
> (specifically the letter `A') that I'd added to an image in Photoshop.
>  This was sufficiently bad to be visible in the print to the naked eye
> ­ and once noticed, it was obvious.  It's not some micro effect that
> only a loupe would reveal.  Once I'd noticed it in the letter A I
> realised it was in all of the sloping parts of the text AND in the
> image area wherever there was a black or very dark sloping edge
> against a much lighter area.
> 
> I tried all sorts of things including checking the head alignment, and
> eventually printing on two different printers.  I then realised it
> must be an artefact of the conversion by the Epson Driver from the
> image resolution (300ppi) to whatever resolution the printer uses.
> The thing that made me realise this was the fact that the exact same
> problem was present when I made the same print from the same image
> file sent to two different printers ­ a 2100 and a 4800.
> 
> For some images I've been using 300ppi as a standard for outputting
> files to print.  But I remembered reading something about Epson
> printers using multiples of 360ppi in the driver.  So I then tried the
> same file resampled in Photoshop from 300ppi to 360ppi.  It totally
> cured the rough jagged edge problem in the printed image.  I've since
> confirmed by other tests that this was not simply as a result of the
> resampling.  This problem seems to occur when you use some simple
> fraction of 360ppi.  For example my 300ppi is 5/6 of the 360ppi, or
> 360ppi is 1/5 more than the 300ppi.  I haven't noticed this problem
> when my image ppi is larger AND not a simple fraction of 360ppi.
> 
> I know that some people use 300ppi as it is often said that this is
> the point at which pixels are no longer visible to the naked eye.  I
> wonder whether your output to print is as sharp as it could be.  My
> experience suggests that if you are printing from an image at 300ppi
> using the Epson Driver, try resampling it to 360ppi in Photoshop for
> printing existing images, and work at 360 ppi for future images.
> 
> I'm writing this up so that if there are others who've puzzled over
> the cause of these jagged hard edges then at least there's a possible
> explanation and cure available.  I somehow think that I can't be the
> only printer who hasn't understood this and acted on it before!
> 
> I'm sure the maths used in resampling will explain this fully, but for
> me avoiding it is what really matters.
> 
> Steve Gledhill
> http://www.virtuallygrey.co.uk/