Re: [APML] Scaling Images, javascript toggle

[George Anderson <georgea@cam.org>]

Absolutely stunning shots!!!

George Anderson
Montreal Quebec

Clear skies and good health

> Thor Olson wrote:
> 
> 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/ManyGlacierLightsOnOff.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."
> 
> -----Original Message-----
> From: Matt BenDaniel [mailto:matt@starmatt.com]
> Sent: Tuesday, November 06, 2001 9:49 PM
> To: astro-photo@seds.org
> Subject: Re: [APML] Scaling Images (was: Cocoon Nebula)
> 
> Mike,
> 
> I used Photoshop JPEG quality=8 for both renditions.
> 
> In GF I used their lossless STN encoding, which purports to capture
> and retain 100.0% of the information in the image.
> 
> JPEG *does* affect pixel layout. It is obvious in Photoshop Save As
> JPEG Dialog and toggle the preview on and off. It is more obvious at
> lower quality levels. It helps to zoom to 200% to see the subtle
> changes when higher quality is used.
> 
> The web image toggling capability is very useful, huh? You can do the
> same thing in PS by switching layers on and off, but it's hard to show
> that to someone else on the internet.
> 
> Matt
> 
> At 10:40 PM 11/6/2001 -0500, Mike Cook, AF9Y wrote:
> >   This is really interesting.  What settings did you use for the
> >jpeg and GF compression?  I can see a grid in both images,
> >but less so in the GF.  The grid lines appear to be the point
> >of shifting.  I thought that jpeg compression was just
> >in the color data and produced no image displacement.
> >
> >
> >Date sent:              Tue, 06 Nov 2001 22:26:27 -0500
> >To:                     astro-photo@seds.org
> >From:                   Matt BenDaniel <matt@starmatt.com>
> >Subject:                [APML] Scaling Images (was: Cocoon Nebula)
> >Send reply to:          astro-photo@seds.org
> >
> >> At 06:16 PM 11/6/2001 +0100, Mikkel Steine wrote:
> >> >...I know from my days in desktop
> >> >publishing that Photoshop is not always the preferred tool for
> scaling images.
> >> >There are numerous techniques for resampling an image, and it
> would be fun to
> >> >try out some of them...
> >>
> >> Mikkel,
> >>
> >> I downloaded the free evaluation version of Genuine Fractals. Using
> GF I scaled the image
> >> down to the exact same size (703x640) as my PS JPG and uploaded it
> to my web site:
> >>
> >> http://people.ne.mediaone.net/mbendaniel1/gallery/astro/cocoon.html
> 
> >>
> >> You can toggle to the PS scaled by moving mouse over image.
> >>
> >> The pixels patterns resulting from GF are slightly different than
> Photoshop bicubic. The
> >> GF stars are sharper and less smeared. The JPG size of the GF image
> is larger, which may
> >> be an indication that GF preserves more information from the
> original image.
> >>
> >> It is very curious how the image annoyingly shifts around when you
> toggle between the two.
> >> Could PS or GF be screwing up its scaling? -- Matt BenDaniel
> http://starmatt.com
> >>
> >>
> >> --  APML Archives at <http://astro.umsystem.edu/apml/>  ---
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> >>
> >
> >
> >
> >Mike Cook, AF9Y
> >http://www.webcom.com/af9y
> >mwcook@cris.com
> >
> >
> >
> >
> >--  APML Archives at <http://astro.umsystem.edu/apml/>  ---
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> 
> --
> Matt BenDaniel
> http://starmatt.com
> 
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