Highest voted questions tagged pbrt-v3 - Computer Graphics Stack Exchange most recent 30 from computergraphics.stackexchange.com 2022-01-27T02:15:52Z https://computergraphics.stackexchange.com/feeds/tag?tagnames=pbrt-v3&sort=votes https://creativecommons.org/licenses/by-sa/4.0/rdf https://computergraphics.stackexchange.com/q/10728 3 Plotting pbrt-v3 Gaussian filter Vertexwahn https://computergraphics.stackexchange.com/users/5891 2021-03-11T21:46:42Z 2021-03-12T19:53:16Z <p>I want to plot the <a href="https://github.com/mmp/pbrt-v4/blob/08418214e4df767a4e6aa95230821e05f3621da9/src/pbrt/filters.h#L80" rel="nofollow noreferrer">Gaussian filter of pbrt-v4</a> with a radius <span class="math-container">$(100,100)$</span> and a standard deviation (<span class="math-container">$\sigma$</span>) of <span class="math-container">$0.5$</span>.</p> <p>I would expect something like this:</p> <p><a href="https://i.stack.imgur.com/4vlMD.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/4vlMD.png" alt="enter image description here" /></a></p> <p>When I plot the pbrt-v4 Gaussian filter with radius <span class="math-container">$(100,100)$</span> and <span class="math-container">$\sigma=0.5$</span> I get:</p> <p><a href="https://i.stack.imgur.com/amEEn.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/amEEn.png" alt="enter image description here" /></a></p> <p>Is the 2nd plot correct? I varied the radius form <span class="math-container">$1$</span> to <span class="math-container">$1000$</span> but the the filter size changes only 2 pixels in total (I get a similar results). Any ideas? How does the correct plot look like?</p> https://computergraphics.stackexchange.com/q/10345 1 Why is there a T factor in the definition of Shah given in Matt Pharr's Physically Based Rendering? Eugene https://computergraphics.stackexchange.com/users/15133 2020-10-26T13:52:29Z 2020-10-26T13:59:44Z <p>The specific chapter about this is here - <a href="http://www.pbr-book.org/3ed-2018/Sampling_and_Reconstruction/Sampling_Theory.html" rel="nofollow noreferrer">Sampling Theory</a><br> Unlike what I read anywhere else, it defines Shah as: <span class="math-container">$$Ш_T(x)=T\sum\nolimits_i{\delta{(x-Ti)}}$$</span> And the T is still present in the reconstructed function: <span class="math-container">$$f\tilde(x)=T\sum\limits_{i=-\infty}^\infty{f(iT)r(x-iT)}$$</span> where r(x) is a reconstruction filter.<br> Everywhere else I can find gives: <span class="math-container">$$s_T{(x)}=\sum\nolimits_i{\delta{(x-Ti)}}$$</span> Can someone work out the maths for me? Why is the difference?</p> <p>I haven't been doing maths for years, and even back in my school days, I don't think I was a good student, so please be gentle.</p> https://computergraphics.stackexchange.com/q/12114 0 Why RGB value bigger than 1 when convert from spectrum in PBRT-V3 Chris Guo https://computergraphics.stackexchange.com/users/16730 2021-08-10T02:36:48Z 2021-08-10T02:49:12Z <p>In PBRT-V3, the light has following spectrum in scene file(Note that the scene file is not come from PBRT itself):</p> <pre><code>&quot;spectrum&quot; [400.0 0.0 500.0 8.0 600.0 15.6 700.0 18.4] </code></pre> <p>then it's converted to following RGB in C++:</p> <pre><code>&quot;rgb&quot; [20.7467213 10.8233843 2.76458955] </code></pre> <p>is this correct? Why the RGB value exceeds 1? Whether this is used to indicate light intensity?</p> https://computergraphics.stackexchange.com/q/9883 0 An equation about PDFs and differentials in the book of pbrt-v3 chaosink https://computergraphics.stackexchange.com/users/5944 2020-05-25T10:00:31Z 2020-05-25T10:00:31Z <p>Why does the equation at the bottom of the following page hold?</p> <p><a href="http://www.pbr-book.org/3ed-2018/Monte_Carlo_Integration/Transforming_between_Distributions.html" rel="nofollow noreferrer">http://www.pbr-book.org/3ed-2018/Monte_Carlo_Integration/Transforming_between_Distributions.html</a></p> <p><span class="math-container">$p(\theta,\phi)d\theta d\phi=p(\omega)d\omega$</span></p> <p>Is this a conclusion of probability and measure theory?</p>