Second Life Forums Archive - Concepts - Redundant Textures Stored Separately?

Kex Godel

Master Slacker

Join date: 14 Nov 2003

Posts: 869

04-06-2004 11:58

Question to the Lindens (or anyone who wants to speculate):

Does the asset server detect if two residents upload the exact same texture?

I ask this because I'm wondering if the free textures provided on several websites are being uploaded multiple times to SL, meaning we could probably be downloading and storing the same texture several times, when only once would really be necessary.

Malachi Petunia

Gentle Miscreant

Join date: 21 Sep 2003

Posts: 3,414

04-06-2004 12:25

I would guess that there is no texture comparison for 1.5 very good reasons:

1) Comparing all uploads with all textures on the asset server is a NP-complete problem. That is, without some sort of preprocessing, you'd have to compare every upload to every extant texture which has complexity O(n^2).
1.5) Even things like MD5 checksums would only catch a subset of the duplicates as even a change to the image meta-data (e.g. EXIF) - not to mention scaling or compression factor changes - would invalidate comparison.

Just a guess.

Candie Apple

Senior Mumbler

Join date: 1 Apr 2003

Posts: 477

04-06-2004 14:33

A few of us were in a conversation with Philip about 2 weeks ago, and this was one thing discussed.

When an individual uses the same texture on multiple objects, it is loaded to clients only once. So individuals re-using textures on multiple objects is a good thing.

If additional residents use that same texture, however, the load is the same for each. The system does not detect if the same texture is being re-used by multiple people, and implementing a 'shared pool' would be extremely time consuming.

Candie

_____________________

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Quitting SL since Dec 2002!

Azelda Garcia

Join date: 3 Nov 2003

Posts: 819

04-06-2004 21:58

> Comparing all uploads with all textures on the asset server is a NP-complete problem. That is, without some sort of preprocessing, you'd have to compare every upload to every extant texture which has complexity O(n^2).

NP-hard means something going as the exponential. Polynomials are not NP-hard: you can actually compute the result for real d. NP-hard cannot be computed at all for d > something very small.

Comparing an uploaded texture with current textures is polynomial, even linear, with the number of textures in the system. It goes as Od, where O is a constant, and d is the number of textures already in the system.

You can reduce the size of O, the constant, by using MD5 checksums.

Jarod Godel

Utilitarian

Join date: 6 Nov 2003

Posts: 729

04-08-2004 10:47

Key queries.

It all gets reduced down to key queries.

_____________________

"All designers in SL need to be aware of the fact that there are now quite simple methods of complete texture theft in SL that are impossible to stop..." - Cristiano Midnight

Ad aspera per intelligentem prohibitus.

Concepts - Redundant Textures Stored Separately?
Kex Godel Master Slacker Join date: 14 Nov 2003 Posts: 869	04-06-2004 11:58 Question to the Lindens (or anyone who wants to speculate): Does the asset server detect if two residents upload the exact same texture? I ask this because I'm wondering if the free textures provided on several websites are being uploaded multiple times to SL, meaning we could probably be downloading and storing the same texture several times, when only once would really be necessary.
Malachi Petunia Gentle Miscreant Join date: 21 Sep 2003 Posts: 3,414	04-06-2004 12:25 I would guess that there is no texture comparison for 1.5 very good reasons: 1) Comparing all uploads with all textures on the asset server is a NP-complete problem. That is, without some sort of preprocessing, you'd have to compare every upload to every extant texture which has complexity O(n^2). 1.5) Even things like MD5 checksums would only catch a subset of the duplicates as even a change to the image meta-data (e.g. EXIF) - not to mention scaling or compression factor changes - would invalidate comparison. Just a guess.
Candie Apple Senior Mumbler Join date: 1 Apr 2003 Posts: 477	04-06-2004 14:33 A few of us were in a conversation with Philip about 2 weeks ago, and this was one thing discussed. When an individual uses the same texture on multiple objects, it is loaded to clients only once. So individuals re-using textures on multiple objects is a good thing. If additional residents use that same texture, however, the load is the same for each. The system does not detect if the same texture is being re-used by multiple people, and implementing a 'shared pool' would be extremely time consuming. Candie _____________________ ================== Quitting SL since Dec 2002!
Azelda Garcia Azelda Garcia Join date: 3 Nov 2003 Posts: 819	04-06-2004 21:58 > Comparing all uploads with all textures on the asset server is a NP-complete problem. That is, without some sort of preprocessing, you'd have to compare every upload to every extant texture which has complexity O(n^2). NP-hard means something going as the exponential. Polynomials are not NP-hard: you can actually compute the result for real d. NP-hard cannot be computed at all for d > something very small. Comparing an uploaded texture with current textures is polynomial, even linear, with the number of textures in the system. It goes as Od, where O is a constant, and d is the number of textures already in the system. You can reduce the size of O, the constant, by using MD5 checksums.
Jarod Godel Utilitarian Join date: 6 Nov 2003 Posts: 729	04-08-2004 10:47 Key queries. It all gets reduced down to key queries. _____________________ "All designers in SL need to be aware of the fact that there are now quite simple methods of complete texture theft in SL that are impossible to stop..." - Cristiano Midnight Ad aspera per intelligentem prohibitus.

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Concepts - Redundant Textures Stored Separately?