I've been pleasantly surprised by the quality of Opera's smooth zooming of
true color images. Especially when scaling down a large image, I truely
like the result. Sharper, crisper and more detailed than linear and bicubic
filtering, and without the artifacts one would see with unsharp masks.

I'd really like to know what kind of filter is used in Opera. It looks
quite suited for my PHP Photo software :)

Example:

Original (2.1MiB)
http://images.fok.nl/upload/041201_7128_mobielzonnebloem3.jpg

Scaled to 20%, The Gimp, linear:
http://nexel.student.utwente.nl/screenshots/ScreenshotD49C6D8A.png

Scaled to 20%, The Gimp, bicubic:
http://nexel.student.utwente.nl/screenshots/Screenshot373122FE.png

Scaled to 20%, Opera.
http://nexel.student.utwente.nl/screenshots/ScreenshotB882CCCC.png

--
Randy Simons

From:	Randy Simons
Subject:	Re: Smooth zooming of images: what filter used?
Date:	Mon, 6 Dec 2004 18:49:20 +0000 (UTC)

Randy Simons wrote:

> I'd really like to know what kind of filter is used in Opera. It looks
> quite suited for my PHP Photo software :)

Hmm, still no concrete answer. Is it a secret or what?..

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Randy Simons

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From:	Josef W. Segur
Subject:	Re: Smooth zooming of images: what filter used?
Date:	Tue, 07 Dec 2004 11:55:20 -0500

On Mon, 6 Dec 2004 18:49:20 +0000 (UTC), Randy Simons wrote:

>Randy Simons wrote:
>
>> I'd really like to know what kind of filter is used in Opera. It looks
>> quite suited for my PHP Photo software :)
>
>Hmm, still no concrete answer. Is it a secret or what?..

The setting has no effect on Win9x systems, IOW it is not a filtering
operation performed in Opera's code.

I believe it is accomplished using HALFTONE in SetStretchBltMode, see
.

--
Joe

From:	Randy Simons
Subject:	Re: Smooth zooming of images: what filter used?
Date:	Tue, 7 Dec 2004 18:15:46 +0000 (UTC)

Josef W. Segur wrote:

> The setting has no effect on Win9x systems, IOW it is not a filtering
> operation performed in Opera's code.
>
> I believe it is accomplished using HALFTONE in SetStretchBltMode, see
> .

Interesting! The person in this posting http://tinyurl.com/3p6cw also
notices the mild sharpning-effect of the halftone-stretching. But he's also
looking for the algorithm, and so am I..

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From:	Randy Simons
Subject:	Re: Smooth zooming of images: what filter used?
Date:	Sun, 12 Dec 2004 10:38:32 +0000 (UTC)

Randy Simons wrote:

> Interesting! The person in this posting http://tinyurl.com/3p6cw also
> notices the mild sharpning-effect of the halftone-stretching. But he's
> also looking for the algorithm, and so am I..

I thought I had it: Wine! But no sigar. From the Wine source:

if (mode == STRETCH_HALFTONE) /* FIXME */
mode = STRETCH_DELETESCANS;

Bah :( Running out of options..

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From:	Eik
Subject:	Re: Smooth zooming of images: what filter used?
Date:	Thu, 09 Dec 2004 17:29:34 -0000

On Tue, 07 Dec 2004 11:55:20 -0500, Josef W. Segur
wrote:

> On Mon, 6 Dec 2004 18:49:20 +0000 (UTC), Randy Simons
> wrote:

>>> I'd really like to know what kind of filter is used in Opera. It looks
>>> quite suited for my PHP Photo software :)

> I believe it is accomplished using HALFTONE in SetStretchBltMode, see
> .

There's a free image resizing tool for Windows XP which (I think) uses
this method too. Enlarging images certainly produces far better results
than GIMP. It's a bit fiddly to resize the dimentions you want but it may
be of use? It's 521KB:

[ http://www.microsoft.com/windowsxp/using/digitalphotography/learnmore/tips/eschelman2.mspx
]

After you right click on an image file (from Explorer) and select 'Resize
Images', you have to click the 'Advanced' button and select the 'Custom'
option. Then enter the width or height you want to resize too. Note that
this tool always preserves the image ratio and resizes it to the largest
dimentions that will fit into the custom screen size you enter. So if you
take a 100x100 image and set it to resize to fit a 300x200 screen, it will
actually be resized to 200x200 rather than 200x300.

Does anyone know of a similar (and free!) XP utility that also uses
halftone but lets you stretch images and resize to a percentage as well as
a fixed number of px?

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From:	Steven V. Gunhouse
Subject:	Re: Smooth zooming of images: what filter used?
Date:	Fri, 10 Dec 2004 03:10:19 GMT

On Thu, 09 Dec 2004 17:29:34 -0000, Eik wrote:

> On Tue, 07 Dec 2004 11:55:20 -0500, Josef W. Segur
> wrote:
>
>> On Mon, 6 Dec 2004 18:49:20 +0000 (UTC), Randy Simons
>> wrote:
>
>>>> I'd really like to know what kind of filter is used in Opera. It looks
>>>> quite suited for my PHP Photo software :)
>
>> I believe it is accomplished using HALFTONE in SetStretchBltMode, see
>> .
>
> There's a free image resizing tool for Windows XP which (I think) uses
> this method too. Enlarging images certainly produces far better results
> than GIMP. It's a bit fiddly to resize the dimentions you want but it
> may be of use? It's 521KB:
>
> [ http://www.microsoft.com/windowsxp/using/digitalphotography/learnmore/tips/eschelman2.mspx
> ]
>
> After you right click on an image file (from Explorer) and select
> 'Resize Images', you have to click the 'Advanced' button and select the
> 'Custom' option. Then enter the width or height you want to resize too.
> Note that this tool always preserves the image ratio and resizes it to
> the largest dimentions that will fit into the custom screen size you
> enter. So if you take a 100x100 image and set it to resize to fit a
> 300x200 screen, it will actually be resized to 200x200 rather than
> 200x300.
>
> Does anyone know of a similar (and free!) XP utility that also uses
> halftone but lets you stretch images and resize to a percentage as well
> as a fixed number of px?
>

You might try IrfanView. It's a free viewer with support for Photoshop
"filters", it supports a huge number of formats, etc.

It supports 6 different "resample" methods, but since no one is sure what
the method you're referring to is actually called (and since I have
Windows 98 SE and thus don't actually see the same effect here in Opera) I
can't say if that is one of them.

Just go to www.irfanview.com and check it out. As it is free (and not
spyware), nothing to lose if it doesn't do what you want.

--
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From:	Eik
Subject:	Re: Smooth zooming of images: what filter used?
Date:	Wed, 01 Dec 2004 20:54:23 -0000

On Wed, 1 Dec 2004 20:21:58 +0000 (UTC), Randy Simons
wrote:

> I'd really like to know what kind of filter is used in Opera. It looks
> quite suited for my PHP Photo software :)

> Scaled to 20%, The Gimp
> Scaled to 20%, Opera.

Judging by the square of soil in the bottom right corner, I'd say Opera
resamples and then sharpens. The almost border-like outline around the
leaves may suggest they also adjust the colour levels?

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From:	Randy Simons
Subject:	Re: Smooth zooming of images: what filter used?
Date:	Wed, 1 Dec 2004 21:05:15 +0000 (UTC)

Eik wrote:

> Judging by the square of soil in the bottom right corner, I'd say Opera
> resamples and then sharpens. The almost border-like outline around the
> leaves may suggest they also adjust the colour levels?

Jeroen did some extra testing:

http://home.student.utwente.nl/j.oortwijn/test/test.htm

It indeed looks like some mild sharpning. However, sharpning is quite CPU
expensive in my experiences.

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Randy Simons

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From:	Jernej Simon+AQ0-i+AQ0-
Subject:	Re: Smooth zooming of images: what filter used?
Date:	Wed, 1 Dec 2004 22:28:18 +0100

on Wed, 1 Dec 2004 20:21:58 +-0000 (UTC), Randy Simons wrote:

> I've been pleasantly surprised by the quality of Opera's smooth zooming of
> true color images. Especially when scaling down a large image, I truely
> like the result. Sharper, crisper and more detailed than linear and bicubic
> filtering, and without the artifacts one would see with unsharp masks.

In my experience, Opera performs pretty bad when scaling between 50 and
200%, but much better than many other programs outside this range...

(I remember looking at some page that dealed with various resizing
algorithms, and the "no filter" image that was simply let to be scaled by
the browser [intended to look pixelated] looked much better to me than any
of the other samples on page).

--
begin .sig
< Jernej Simon+AQ0-i+AQ0- ><>+Jco-<>< http://www2.arnes.si/~sopjsimo/ >
< jernej simoncic at isg si >< http://deepthought.ena.si/ >
end