Re: [Algorithms] Filtering
Brought to you by:
vexxed72
Menu
▾
▴
Re: [Algorithms] Filtering
|
From: Andreas B. <and...@gm...> - 2010-10-01 19:51:58
|
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 <ola...@gm...> 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" <na...@io...>
> To: "Game Development Algorithms" <gda...@li...>
> 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
>>> <and...@gm...> 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
>>> GDA...@li...
>>> 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
>>> GDA...@li...
>>> 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
>>> GDA...@li...
>>> 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
>> GDA...@li...
>> 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
> GDA...@li...
> https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list
> Archives:
> http://sourceforge.net/mailarchive/forum.php?forum_name=gdalgorithms-list
>
|
