PSCS interpolation options

[Doug_Katz@adobeforums.com]

I'm trying to follow the logic that I've recently read of using Bicubic Smoother
for upsampling an image and Bicubic Sharper for downsampling. If upsampling's
gonna "soften" my image by interpolating pixels, my pea brain says SHARPEN as I
interpolate, not smoothe. Why wouldn't I want to sharpen going up?

The only answer I've conjured on my own is that Smoother somehow protects
against artifacts. Is this it? And if it is, why wouldn't I want to use Smoother going
down as well? Why Sharper down?

I also understand (and see in my own experiments) that these new options produce
subtle differences at best. Nothing dramatic here. Are my eyes seeing correctly?

Thanks.

[Peter_Figen@adobeforums.com]

Doug,

If you use the Sharpen option for uprezzing, you are more likely to see stairstepping in diagonals. The Smoother option, however subtle it is, seems to attempt to fight this tendency. In my testing, I usually find the standard Bicubic works the best, but it really depends on the image and, as you have already noted, the differences are quite small indeed.

[Father_Blaise@adobeforums.com]

Hello Doug,

According to Real World Photoshop Bicubic Smoother is always a better option unless you are upsampling greyscale to make lineart.

Sincerely,

FB

[Doug_Katz@adobeforums.com]

Thank you, gentlemen. Father B, does that mean B. Frazer does not recommend
the Sharpen option for ANY situation (other than the one you noted)? And, for
that matter, does he not recommend the ol' standby either (the Bicubic we've
had for several versions)?

Thanks again.

[Buko@adobeforums.com]

the Bicubic we've had for several versions)?




I don't think its the same bicubic either.

[Ramón_G_Castañeda@adobeforums.com]

FB,

The Real World Photoshop you quote must be for the old version of Photoshop (7.x), unless you got a hold of the new edition for Photoshop 8 (CS) which has been announced but is not shipping yet.

Bicubic changed in Photoshop CS (8 ), so your comments wouldn't apply to Doug's version-specific question. If I'm wrong, please enlighten me.

Moreover, what Doug is interested in finding out is why Bicubic Smoother is better suited than Bicubic Sharper for upsampling but not for downsampling.

[Doug_Katz@adobeforums.com]

Exactamente, señor! Muchas gracias.

[Ramón_G_Castañeda@adobeforums.com]

De nada, mi estimado amigo. ¡Ojalá yo supiera la respuesta!

[Doug_Katz@adobeforums.com]

So, meanwhile, anybody got a clue here? Even if no one knows what the
"theory" is underlying the advice, I'd love to know what you guys are
actually USING? Because based on the few posts here and other things
I've read, I'm more confused now than ever. Are most of you just
using the "new and improved" Bicubic? Is anyone using Sharper for
any type of situation? Is anyone using Smoother?

[Buko@adobeforums.com]

I've upresed stuff using smoother. thats why I brought it up.

[Father_Blaise@adobeforums.com]

I apologise! I was confusing versions of photoshop and I didn't realize at the time that PSCS had two new options. I should have been more careful!

I thought the discussion was about bicubic vs. bilinear or nearest neighbor.

I am sorry for the confusion.

Sincerely,
FB

[Doug_Katz@adobeforums.com]

Father, your... er... sin is forgiven. After all, I'm sure you knew not what you did :)

[JasonSmith@adobeforums.com]

As Peter mentioned - the theory (as I interpret it at least) is that with uprezing you dont want the harsh stair stepping - hence a smoother option exists.

With downrezing you want to mantain as much detail as possible, and I dont see how that can be accomplished with smoother resampling - hence the sharper interpolation.

[Doug_Katz@adobeforums.com]

OK. That actually makes sense.