Subject: Scaling to get accurate preview

[Alfredo Mateus <almateus@globalsite.com.br>]

> Sender: Broker@ComPorts.com
> To: ff@aurdev.com
> From: Broker <Broker@ComPorts.com>
> Subject: Scaling to get accurate preview
> 
Broker, this time you sent to the right address, but it bounced to me
again with the message:
Re: BOUNCE ff@seabrook.aurdev.com:    Non-member submission from [Broker
<Broker@ComPorts.com>]

This means one of two things: you are not subscribed or you sent the
message from an address different from the one you subscribed. The list
is closed to non-members to avoid spam. If you need help in subscribing
drop me a note (almateus@globalsite.com.br). Or send a message to
majordomo@aurdev.com with who ff in the body to see what is the address
you subscribed.

Alf

> Hello all,
> 
> Not sure if this was posted (I mailed to wrong address), but I asked about
> how to code to get an accurate preview:  "I still struggle with inaccurate
> preview windows.  I've read  Mario's comments in the FFPG, and I still
> don't get it.  Can any FF program  create an accurate preview window if
> coded properly?  I'd sure like some  assistance in that area!"
> 
> Alf responded with:
> >Yes, FF can make accurate previews for any size of image. You just have
> >to take care to scale things. Let's say you type this code:
> >
> >R: x
> >G: x
> >B: x
> >
> >If your image is 256 pixels wide, you should see a gradient from black
> >(x=0) to white (x=255).  If your image is 400 pixels wide, you will see
> >a gradient from black to white and then a white bar on the right,
> >starting on the pixel 255 up to the pixel 399, since FF cannot assign a
> >value greater than 255 for the color. How do you get around this? You
> >use the scale function:
> >
> >R:G: and B: scl(x,0,X,0,255)
> >
> >You can read this as "take x and scale it from 0 to X (the width of the
> >image) to from 0 to 255. This will give you the correct b/w gradient for
> >a picture with any width. Of course other codes will be much harder to
> >scale, and maybe you already knew this, bnut it is a start. Hey, this is
> >not that much math! You don't need to know integrals and derivatives to
> >create a filter!
> 
> Thank you!
> I follow this, and it works for me.  I often have inaccurate preview
> windows when using m, d and trig functions.
> 
> Is the scl function always the last thing you do? (i.e. the outermost
> function)
> 
> Do I have to do it for all channels to make the preview accurate?  (I
> realize I might want to do it for all channels for image effect reasons.)
> 
> Are there rules of thumb for dealing with products, quotients, logical
> combinations ( ^, &, |), etc?  Or, do I just experiment and see what gives
> the best preview rendition?
> 
> One more question:  How often does the digest sent out?
> 
> TIA,
> 
> Broker