> Richard
Since the standard advice with USM has always seemed to me to be check
at 100% on screen do I guess your 50% screen advice assumes a 300ppi
file is being used and printed on 150lpi screen? Logically for regular
litho work this seems like very good advice. <

Paul, I would not expect or say that an even reduced screen magnification to
accurately represent lpi effects, but it can help in some cases (the new
view command is good to have two windows in use).

I recently posted this message to the Colour Theory list, perhaps it will
help:

>> After my reply on recovery of poor looking files - I
thought I may as well bring up a point for discussion - Photoshop
view magnification when evaluating image quality.

Most users are aware that 1:1 or 100% view provides an uninterpolated
true view of the image content, which is often advised when
evaluating USM effects (while the brain does it's trick of factoring
in what output will do to the image based on experience). The 50%
view is often helpful for helping to see what the expected averaging
process of output will do - although even at such as simple reduced
magnification there are artifact problems and the image can't be
trusted to display repeating patterns or fine detail with accuracy.

Often an image which looks like a sows ear at 100% view will output
looking much closer to a silk purse - with no extra effort on your
part. Even more so if there is more data in the file than required
for the current repro size and conditions. Often viewing the original
at 50% magnification for most files, or 25% for really large files
will do a great job of showing the expected output.

I still use 100% view for evaluating USM moves - but I do find that
50% or 25% views can often change how one applies the threshold
command when sharpening to avoid noise or grain. I might end up using
a 'noisier' setting at 100% view, as my experience and the reduced
even view show that this noise amplification makes no difference to
the output, even though the same size view may be a little bit ugly.

When dust spotting a one off scan that will be reduced in layout -
100% view is more than enough, as you can count on the output process
to hide many of the smaller artifacts (unless you are selling a clean
scan that is <g>, in house may have different rules than for external
clients). Using an uneven view like 66% can amplify some of the
larger spots which are worthy of attention, while hiding smaller
spots that can be safely missed in the manual cleanup.

The same can be said for grain reduction or artifact cleaning - does
your experience and a 50% reduced zoom view show that cleaning is
required? The 1:1 view can sometimes be misleading, depending on the
image and the output and other factors. <<

Stephen Marsh.






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