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DeFi
11-28-2005, 07:43 PM
Hello,
I'm using PS7 with WinXP and just discovered a strange behaviour of the build in bicubic image scaling algorithm. Images start to get jaggie when scaled down by more than 50%. With Fireworks or even ImageReady the quality is much better. However it's possible to work around this by scaling the image down in more than one step. It would be nice if you could tell me, if this is a known bug of the build in scaling algorithm, or if it occurs only on my machine.

Thanks
DeFi

BlueFlare
11-28-2005, 09:06 PM
I never noticed any problem with Photoshop (I use CS/CS2) when I resize with less than 50%.
I even tested it for you with several images; no jaggies.

Make sure that you view the image after you resize at 100%.

DeFi
11-28-2005, 09:41 PM
Ok, I see it might be better to post an example:

Image scaled down with Photoshop7 in in one step (http://www.defi1.de/files/images/q_ps7.jpg)
Image scaled down with Photoshop7 in two steps (http://www.defi1.de/files/images/q_ps7sw.jpg)

It's clearly visible, that the first picture has kind of aliasing problems.

The original highres picture can be found here: http://forums.cgsociety.org/showthread.php?t=272971

jbw
11-28-2005, 11:11 PM
I've always been advised to scale images in steps, using unsharp mask in between scaling to prevent blurring as much as possible.

ta,
jbw

halo
11-28-2005, 11:15 PM
i think it is a bug...cant remember if it got fixed, but i seem to remember having the same problems in 7 on my mac, and cant remember the same in CS2 now.

perhaps a quick look at the adobe photoshop forums may hold the answer :)

BlueFlare
11-29-2005, 01:32 AM
I've always been advised to scale images in steps, using unsharp mask in between scaling to prevent blurring as much as possible.
No need for that anymore if you have CS/CS2, which has Bicuc Sharper.

DeFi, I can now see what your problem is, but still, I don't see these artifacts in CS after I took the high resolution 1600 image and resampled it to 684 wide like your image. Actually, with Bicuc Sharper it even looks better than the one you sampled twice. Like Halo said, it must be a bug and probably limited to earlier versions of CS.

zman
11-29-2005, 07:44 AM
interesting.
When I size down an image I allwais use cubic, apply a sharp filter and fade it to 40%. (PS CS1)

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