Re: Dpi and line screen
Re: Dpi and line screen
- Subject: Re: Dpi and line screen
- From: Ernst Dinkla <email@hidden>
- Date: Mon, 02 Jan 2006 15:42:57 +0100
jc castronovo wrote:
----- Original Message ----- From: "Ernst Dinkla
The usual ratios mentioned for acceptable work fall between 1.40 and 2
x. I have always assumed that the lowest acceptable quality was at the
root value 1.41...x, in conventional screening corresponding with the
45 degree angle of one of the screens the digital image at 0/90 degree
has to be converted to (the other angles but the 0 degrees need a
similar factor). The 2x being the maximum needed in view of Nyquist.
With stochastic screening etc and better upsampling + print sharpening
possible on digital images these days the lowest ratio may have
dropped to 1:1 for the digital images to start from. Most of time this
ratio number isn't an issue at all with today's quality of digital
images and cheap memory. Is the extra time and space needed for 2x a
real problem ?
It's not the time or cost, but sometimes it just isn't available from
the source image. What is the wisdom of scaling up a low resolution
image only to scale it back down again?
john
Let's say the upsampling routines in digital image editors are
much better than the down sampling you get with screening at a
too low image resolution. Seems reasonable to me but I can't
build on much experience.
For example I wonder what actually happens with an image that
is turned 45 degrees in Photoshop. There's degradation every
time you do that but some smart algorithms could reduce that
effect. If the image is virtually upsampled with a 1.41... or
2 x factor, turned and brought back to the original resolution
there should be less loss.
Bicubic upsampling, anti-aliasing at the downsampling. If
screening algorithms have similar approaches it would be
different. But you can't use the same tricks on bitmaps that
are allowed on the original image. Much depends on the stage
where the actual screening starts and what is done after that.
The screens have to represent the original image but they also
need to suit the printing process. I don't know what
compromises have to be made. Must be complicated.
--
Ernst Dinkla
www.pigment-print.com
( unvollendet )
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Colorsync-users mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden