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Negative LOD Bias

Discussion in 'Bob's Track Builder' started by mianiak, Dec 4, 2009.

  1. I have been doing a lot of learning about texture quality for the last few weeks and there is one thing I am struggling to understand, which is negative LOD Bias.

    I notice that nearly all of the textures that come with Xpacks have a neg. LOD of -4.
    When I use those in the track I get very bad aliasing. If i set my neg. LOD to clamp in the Nvidia profiler it looks great. So I go and adjust all the negative values on the textures to 0 and I get rid of all the aliasing in the game and the textures still look nice. The only thing I notice that makes textures with a neg. LOD of -4 look good is Antialiasing transparency, but AA transp. takes a lot of processing power.
    My system can quite easily handle high quality settings but when I create a track I like to leave the settings at default so I can cover the average user.

    My question is.. Is it a code of practice to set neg. LOD bias like this so that people with high end computers can have clear clean looking textures with all their AA turned on and people with low end computers can chose to clamp and have less clear textures?
    I am struggling to decide weather to leave all the neg. LOD at 0, or be more considerate to people with high end systems and set it to -4. But at the same time, who would know to set clamp on to fix an aliasing issue?
    I am thinking that if I want to make the average person happy, it's best to set it at 0, because people who don't know the technical side of computers will otherwise instantly be unsatisfied with the track. It's all too confusing for me atm :D

    [ED] forgot to mention, I know what neg. LOD bias is, I just don't know how to use it to it's advantage.
  2. hi, hum, I can not help you, but I wondered this question several times, why a BIAS negative value?, interesting question really, I hope somebody could clear this.

  3. A quick Google search turned up this:

    "Negative LOD BIAS

    The so called Level of Detail BIAS(LOD BIAS) controls which at which distance from the viewer the switch to lower resolution mip maps takes place (see here for more details about mip maps). The standard value of the LOD BIAS is 0.0 (zero). If you lower the LOD BIAS below zero, the mip map levels are moved farther away, resulting in seemingly sharper textures. But if the scene is moving, the textures start to shimmer.

    Because of this, it's not a good idea to use a lower LOD BIAS to improve the sharpness of the image. It's better to use an Anisotropic Filter instead.

    Some games force a negative LOD BIAS nevertheless. The result is heavy texture shimmering. To avoid this, the driver can clamp the LOD BIAS to zero. That means that the LOD BIAS can still be raised above zero, but it cannot set lower than zero.

    In the current drivers, the LOD clamp is always active if you're using the High Quality setting."

    So it seems that setting LOD=0 is probably the right answer. Especially for road & shoulder textures, where shimmering is often complained about.
  4. hi,in my last circuit, i m having lot of problems with flickering textures, I didnt know why, because some of them are used in previous circuits, I m going to see lod values, hum

  5. Emery thanks for taking the time to reply :) . That is exactly what I learnt and exactly why I asked. I can't understand why they are set to -4 when this shimmering/aliasing issue is so apparent.