Re: Filtering
Adrian Bentley <[email protected]> Sat, 2 Oct 2010 18:44:07 -0700
| Newsgroups | gmane.games.devel.algorithms |
|---|---|
| Message-ID | <[email protected]> |
FYI, DirectX 11 claims: "Require 8-bits of subtexel and sub-mip precision on texture filtering" It doesn't appear to say anything about precision of the resulting color. I would think subtexel precision usefulness would be at least somewhat coupled to output precision, but maybe not. Cheers, Adrian On Fri, Oct 1, 2010 at 1:42 PM, Tibor Klajnscek <[email protected]> wrote: > Just wanted to point something out - now that you know it won't work > it probably makes sense to switch to a float32 texture and still do the > filtering manually... you'll at least save the pack/unpack instructions :) > > - Tibor > > On 10/1/2010 9:51 PM, Andreas Brinck wrote: >> Hi Ola, >> >> unfortunately the floating point textures on the platform I'm working >> on don't support bilinear filtering (this is the reason why I stored >> the value in an RGB-texture to begin with). >> >> /Andreas >> >> P.S. Got your Ph.D yet? >> >> On Fri, Oct 1, 2010 at 8:12 PM, Ola Olsson<[email protected]> wrote: >>> While we're throwing ideas around, why not try using a float texture and see >>> if it produces the same error? >>> >>> .ola >>> >>> P.S. >>> Hi Andreas :) >>> >>> ----- Original Message ----- >>> From: "Nathaniel Hoffman"<[email protected]> >>> To: "Game Development Algorithms"<[email protected]> >>> Sent: Friday, October 01, 2010 7:59 PM >>> Subject: Re: [Algorithms] Filtering >>> >>> >>>> Didn't the newer NVIDIA GPUs fix this? >>>> >>>>> You guessed right. The loss of precision is in the texture units. >>>>> Unfortunately, 8 bit components are filtered to 8 bit results (even >>>>> though >>>>> they show up as floating point values in the shader). This is true for >>>>> nvidia gpus for sure and probably all other gpus. >>>>> >>>>> -mike >>>>> ----- Original Message ----- >>>>> From: Stefan Sandberg >>>>> To: Game Development Algorithms >>>>> Sent: Friday, October 01, 2010 1:45 AM >>>>> Subject: Re: [Algorithms] Filtering >>>>> >>>>> >>>>> Assuming you're after precision, what's wrong with doing it manually? >>>>> :) >>>>> If performance is what you're after, and you're working on textures as >>>>> they were intended(ie, game textures or video or something like that, >>>>> not 'data'), you could separate contrast& color separately, keeping >>>>> high contrast resolution, and downsampled color, and >>>>> you'd save both bandwidth and instr. >>>>> If you simply want to know 'why', I'm guessing loss of precision in the >>>>> tex units? >>>>> You've already ruled out shader precision from your own manual >>>>> filtering, so doesn't leave much else, imo.. >>>>> Other than manipulating the data you're working on, which is the only >>>>> thing you -can- change I guess, I cant really see a solution, >>>>> but far greater minds linger here than mine, so hold on for what I >>>>> assume will be a lengthy description of floating point math as >>>>> it is implemented in modern gpu's :) >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> On Fri, Oct 1, 2010 at 9:57 AM, Andreas Brinck >>>>> <[email protected]> wrote: >>>>> >>>>> Hi, >>>>> >>>>> I have a texture in which I use the R, G and B channel to store a >>>>> value in the [0, 1] range with very high precision. The value is >>>>> extracted like this in the (Cg) shader: >>>>> >>>>> float >>>>> extractValue(float2 pos) { >>>>> float4 temp = tex2D(buffer, pos); >>>>> return (temp.x * 16711680.0 + temp.y * 65280.0 + temp.z * 255.0) * >>>>> (1.0 / 16777215.0); >>>>> } >>>>> >>>>> I now want to sample this value with bilinear filtering but when I do >>>>> this I don't get a correct result. If I do the filtering manually >>>>> like >>>>> this: >>>>> >>>>> float >>>>> sampleValue(float2 pos) { >>>>> float2 ipos = floor(pos); >>>>> float2 fracs = pos - ipos; >>>>> float d0 = extractValue(ipos); >>>>> float d1 = extractValue(ipos + float2(1, 0)); >>>>> float d2 = extractValue(ipos + float2(0, 1)); >>>>> float d3 = extractValue(ipos + float2(1, 1)); >>>>> return lerp(lerp(d0, d1, fracs.x), lerp(d2, d3, fracs.x), >>>>> fracs.y); >>>>> } >>>>> >>>>> everything works as expected. The values in the buffer can be seen as >>>>> a linear combination of three constants: >>>>> >>>>> value = (C0 * r + C1 * g + C2 * b) >>>>> >>>>> If we use the built in texture filtering we should get the following >>>>> if we sample somewhere between two texels: {r0, g0, b0} and {r1, g1, >>>>> b1}. For simplicity we just look at filtering along one axis: >>>>> >>>>> filtered value = lerp(r0, r1, t) * C0 + lerp(g0, g1, t) * C1 + >>>>> lerp(b0, b1, t) * C2; >>>>> >>>>> Doing the filtering manually: >>>>> >>>>> filtered value = lerp(r0 * C0 + b0 * C1 + g0 * C2, r1 * C0 + g1 * C1 >>>>> + >>>>> b1 * C2, t) = >>>>> = (r0 * C0 + b0 * C1 + g0 * C2) * (1 - t) + (r1 * >>>>> C0 + g1 * C1 + b1 * C2) * t = >>>>> = (r0 * C0) * (1 - t) + (r1 * C0) * t + ... = >>>>> = lerp(r0, r1, t) * C0 + ... >>>>> >>>>> So in the world of non floating point numbers these two should be >>>>> equivalent right? >>>>> >>>>> My theory is that the error is caused by an unfortunate order of >>>>> floating point operations. I've tried variations like: >>>>> >>>>> (temp.x * (16711680.0 / 16777215.0) + temp.y * (65280.0/16777215.0) + >>>>> temp.z * (255.0/16777215.0)) >>>>> >>>>> and >>>>> >>>>> (((temp.x * 256.0 + temp.y) * 256.0 + temp.z) * 255.0) * (1.0 / >>>>> 16777215.0) >>>>> >>>>> but all exhibit the same problem. What do you think; is it possible >>>>> to >>>>> solve this problem? >>>>> >>>>> Regards Andreas >>>>> >>>>> ------------------------------------------------------------------------------ >>>>> Start uncovering the many advantages of virtual appliances >>>>> and start using them to simplify application deployment and >>>>> accelerate your shift to cloud computing. >>>>> http://p.sf.net/sfu/novell-sfdev2dev >>>>> _______________________________________________ >>>>> GDAlgorithms-list mailing list >>>>> [email protected] >>>>> https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list >>>>> Archives: >>>>> >>>>> http://sourceforge.net/mailarchive/forum.php?forum_name=gdalgorithms-list >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> ------------------------------------------------------------------------------ >>>>> >>>>> >>>>> ------------------------------------------------------------------------------ >>>>> Start uncovering the many advantages of virtual appliances >>>>> and start using them to simplify application deployment and >>>>> accelerate your shift to cloud computing. >>>>> http://p.sf.net/sfu/novell-sfdev2dev >>>>> >>>>> >>>>> ------------------------------------------------------------------------------ >>>>> >>>>> >>>>> _______________________________________________ >>>>> GDAlgorithms-list mailing list >>>>> [email protected] >>>>> https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list >>>>> Archives: >>>>> >>>>> http://sourceforge.net/mailarchive/forum.php?forum_name=gdalgorithms-list------------------------------------------------------------------------------ >>>>> Start uncovering the many advantages of virtual appliances >>>>> and start using them to simplify application deployment and >>>>> accelerate your shift to cloud computing. >>>>> http://p.sf.net/sfu/novell-sfdev2dev_______________________________________________ >>>>> GDAlgorithms-list mailing list >>>>> [email protected] >>>>> https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list >>>>> Archives: >>>>> http://sourceforge.net/mailarchive/forum.php?forum_name=gdalgorithms-list >>>> >>>> >>>> ------------------------------------------------------------------------------ >>>> Start uncovering the many advantages of virtual appliances >>>> and start using them to simplify application deployment and >>>> accelerate your shift to cloud computing. >>>> http://p.sf.net/sfu/novell-sfdev2dev >>>> _______________________________________________ >>>> GDAlgorithms-list mailing list >>>> [email protected] >>>> https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list >>>> Archives: >>>> http://sourceforge.net/mailarchive/forum.php?forum_name=gdalgorithms-list >>> >>> ------------------------------------------------------------------------------ >>> Start uncovering the many advantages of virtual appliances >>> and start using them to simplify application deployment and >>> accelerate your shift to cloud computing. >>> http://p.sf.net/sfu/novell-sfdev2dev >>> _______________________________________________ >>> GDAlgorithms-list mailing list >>> [email protected] >>> https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list >>> Archives: >>> http://sourceforge.net/mailarchive/forum.php?forum_name=gdalgorithms-list >>> >> ------------------------------------------------------------------------------ >> Start uncovering the many advantages of virtual appliances >> and start using them to simplify application deployment and >> accelerate your shift to cloud computing. >> http://p.sf.net/sfu/novell-sfdev2dev >> _______________________________________________ >> GDAlgorithms-list mailing list >> [email protected] >> https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list >> Archives: >> http://sourceforge.net/mailarchive/forum.php?forum_name=gdalgorithms-list >> > > ------------------------------------------------------------------------------ > Start uncovering the many advantages of virtual appliances > and start using them to simplify application deployment and > accelerate your shift to cloud computing. > http://p.sf.net/sfu/novell-sfdev2dev > _______________________________________________ > GDAlgorithms-list mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list > Archives: > http://sourceforge.net/mailarchive/forum.php?forum_name=gdalgorithms-list > ------------------------------------------------------------------------------ Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev _______________________________________________ GDAlgorithms-list mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list Archives: http://sourceforge.net/mailarchive/forum.php?forum_name=gdalgorithms-list