Re: [APML] Scaling Images, javascript toggle

["Arne Danielsen" <arnedani@online.no>]

Very cool shot, Thor!!

Regards,
Arne
--
Arne Danielsen
Langhussenter 15, 1405 Langhus, Norway
mailto:arne.danielsen@oslo.online.no
http://arnedani.home.online.no/
N59°45'14"  E10°50'38" A115m

----- Original Message -----
From: "Thor Olson" <Thor.Olson@EFI.COM>
To: <astro-photo@seds.org>
Sent: Wednesday, November 07, 2001 5:07 AM
Subject: RE: [APML] Scaling Images, javascript toggle


> Matt,
> Jpeg compression is spatially lossy.  It carves the image into 8x8 pixel
> blocks and then does a fourier transform on each, keeping the low order
> large amplitude coefficients and discarding the small amplitude, high
> frequency ones.  The result is that an exact pixel coordinate of a point
> source, like a star, will not be preserved within the 8x8 block, depending
> on how much gets thrown away.
>
> If one jpeg is larger, it indicates that more of the detail is retained.
> I would expect its positions to be more true to the original.  I don't
> know what the Genuine Fractal algorithm does beforehand, so it's not
> clear which is "truer".
>
> BTW, I agree that your image toggle is a very powerful presentation
> tool.  It inspired me to assemble a pair of images, not nearly so dramatic
> as your day-night scenes, but intriguing in its own way.  Here is
> a link to Many Glacier Lights, ala BenDaniel:
>
> http://nightscapes2.home.att.net/photos/startrails/OdysseyTrails/ManyGlacier
> LightsOnOff.html
>
> Thor
>
> Thor Olson
> Color Imaging Scientist            voice:      +1 651 365 5252
> EFI-Minnesota                 email: mailto:thor.olson@efi.com
> web-res astrophotos at:       http://home.att.net/~nightscapes
>
>    "Man has ten, computers have two, Nature has e fingers."
>



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