[opensource-dev] 5 Channel JPEG2000

[Joshua Bell]

On Mon, Jan 10, 2011 at 11:47 AM, Ricky <kf6kjg at gmail.com> wrote:

> Question: what, if anything, is the 5th channel currently used for?
>

Bump maps in baked textures. IIRC, only the avatar pipeline
produces/consumes that channel. Also, IIRC, the logic is entirely
client-side at the moment.


> Could it be used for normal maps if it is currently unused?
> If so, then we could do this entirely clientside, assuming 5 channel
> textures can be uploaded.  Of course there would still need to be a
> way to disable the alpha channel during upload while preserving the
> normal map channel.
>

That would technically be possible. The asset system does do verification
and modification of various asset types on upload (including textures), but
- again, technically - this would probably work, possibly requiring some
minor changes to the asset verifier.

However...

The biggest challenge is the lack of support for multiple channels in
JPEG2000-producing/consuming tools. Many tools only work with 3-channel
images, and complain about 4. Combined with the lack of tools for authoring
JPEG2000 images in the first place, I'm not sure you'd want add another 3
channels to the image for the normal map. It would also mean you couldn't
re-use a normal map with two textures, e.g. to allow color variants on a
base mesh.

Avoiding two separate texture asset fetches (colors and normals) per face
might be a significant win, but I'd want to see the numbers to prove it
first.

(For comparison, the 13-channel RAW data used for uploading/downloading
region terrain and parcel data is pretty pesky to work with. Sure, it works
with PhotoShop, and is a technically simple single file backup format, but
putting all of that data into a single image is fragile that you expect
users to edit is not particularly user-friendly.)


> Ricky
> Cron Stardust
>
> On Monday, January 10, 2011, Joshua Bell <josh at lindenlab.com> wrote:
> > On Mon, Jan 10, 2011 at 9:28 AM, Dave Booth <dave at meadowlakearts.com>
> wrote:
> >
> > Thats a pretty good bit of thinking out loud there, Ponzu....
> >
> > Personally I'd say thats a "clean" fix for this. However it all depends
> > on how things are stored server-side - if the asset server code
> > automatically assumes that every texture has an alpha channel and
> > supplies a "solid" one for those where the upload doesnt provide one,
> > any benefit of specifying at upload time is moot.
> > The asset upload/storage system handles 3, 4 or 5 channel JPEG2000
> textures and doesn't tinker with the channel data. The bulk of the textures
> in the asset system are 3-channel (RGB).
> >
> > (Excellent question, BTW.)
> >
> >
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