23
votes
Accepted
How are mipmap levels computed in Metal?
Mip selection is pretty well standardized across devices today—with the exception of some of the nitty-gritty details of anisotropic filtering, which is still up to the individual GPU manufacturers to ...
- 25.2k
19
votes
Accepted
Why use a tent filter in path tracing?
The theoretical ideal antialiasing filter for discretely sampled data is a sinc filter, because it perfectly removes all frequencies higher than the Nyquist frequency, while leaving alone all the ...
- 25.2k
12
votes
Accepted
Help me grasp Anisotropic Filtering (AF)
To understand the nature of anisotropic filtering, you need to have a firm understanding of what texture mapping really means.
The term "texture mapping" means to assign positions on an object to ...
- 9,932
7
votes
Accepted
Path tracer - multi layered materials and importance sampling
Wenzel Jakob et al presented a framework for layered Materials at SIGGRAPH 2014. Section 6.2 explains importance sampling. If you prefer code over equations, the method is implemented in the Mitsuba ...
- 706
5
votes
Help me grasp Anisotropic Filtering (AF)
A few points that you probably already know, but that I just want to put out there for others reading this. Filtering in this case refers to low-pass filtering like you might get from a Gaussian Blur ...
- 3,441
5
votes
Why use a tent filter in path tracing?
I just looked at Wikipedia articles about Bilinear interpolation.
A tent filter is a kind of Bilinear interpolation.
A Bilinear interpolation interpolates on 2 dimensions.
It first linearly ...
- 1,605
4
votes
Accepted
Pixel dispersion (dissolving) algorithms
A very simple low memory approach
If you really want to use as little memory as possible, it can be done with not much more memory than that required to store a single image (the first frame) ...
4
votes
What does filter mean in glint rendering and texture mapping?
Filtering refers to image processing operations that generate a new image by applying a filter kernel to an existing image. This is used for many purposes, but one of the most common is to resample ...
- 25.2k
4
votes
Accepted
Ray tracing - partial derivatives for texture lookup
Yes, ray differentials are the way to go. The Paper by Igehy introduces them for the use case of filtered texture lookups. When generating the primary rays, you initialise the differentials to reflect ...
- 706
4
votes
Accepted
Kaiser windowed sinc filter for mip mapping
I was curious so I tried it. I used the Kaiser Window from Wikipedia: $\frac{I_0\left(\alpha\sqrt{1-x^2}\right)}{I_0\left(\alpha\right)}$
This page has a slightly different formulation using $\pi\...
- 1,585
4
votes
Accepted
Texture units parameters in OpenGL
Your understanding of the behavior of texture units and state is confused. That's to be expected: OpenGL's pre-DSA API is not making it easy to understand this.
As far as core profile OpenGL is ...
- 9,932
3
votes
Accepted
Is there a quicker way to draw a symmetric, scale-invariant (declining color) gradient around an ellipse?
You can exactly find the distance to a 2D ellipse using the signed distance function of an ellipse. Here is one by iq on shadertoy:
https://www.shadertoy.com/view/4sS3zz
Then a scale invariant way of ...
- 1,283
3
votes
Accepted
Unexpected results from Mitchell-Netravali
Mitchell–Netravali has negative lobes, which are generally not recommended for small sample counts from what I understand; you tend to end up with both the positive and negative areas undersampled. ...
- 25.2k
3
votes
Accepted
Plotting pbrt-v3 Gaussian filter
You probably want to set sigma to be a fraction of the radius, rather than a fixed value. Sigma controls the actual shape of the filter, while radius just controls how far out the filter gets cut off (...
- 25.2k
2
votes
Pixel dispersion (dissolving) algorithms
You could do this entirely within an OpenGL/WebGL fragment shader:
Attach the image you wish to emerge as a texture/sampler2D.
Attach uniforms for the current time, as well as the time you want the ...
- 341
2
votes
Does film filter introduce bias in path tracing?
This is an answer to your comment rather than the title of your question. It can be considered as a partial answer.
The bias in path tracers are introduced by the estimators.
For example, think of the ...
- 446
2
votes
Accepted
How does the GPU know whether to magnify/minify?
Minification vs magnification is an extension of mipmap selection. When you calculate the desired mip level, it can come out to be less than 0 (or in general, less than the sampler's configured ...
- 25.2k
2
votes
Accepted
How do I normalize all pixel values such that all pixel values are 'pulled towards' the mean?
Here are both images "cleaned" using simple luminance thresholding like I suggested in the comments. There was nothing special done to these images, a simple "is the luminance below ...
- 3,354
1
vote
Accepted
Why don't high-res shadow maps produce aliasing artifacts due to minification?
Turns out minification aliasing is a real problem, just as with regular (color) textures. Following are a couple of papers demonstrating the artifacts and presenting solutions (basically low-pass ...
- 121
1
vote
Accepted
Texture prefiltering for Linearly Transformed Cosines
I achieved similar result to theirs. First, the target texture for mip generation is base texture size + two margins, each equals 0.125 of base size.
Then during generation of base mip level, there ...
- 2,179
1
vote
Properties of the image reconstruction filter in rendering
I am replying to the last edit of the question.
You can show that $\|h_j * f \|^2_2 \leq \|h_j\|^2_1\|f\|^2_2$ from Young's theorem. Provided that $\|h_j\|_1 \leq 1$ you have: $\|h_j * f \|^2_2 \leq ...
- 2,226
1
vote
What is a common approach to smooth structures in textures?
I don't have enough rep to add a comment so...
You could use a post process based anti-aliasing technique like FXAA or SMAA. Also, if performance is not a priority, you could go for SSAA. Another ...
- 110
1
vote
Suggested image preprocessing before applying threshold
In your case, I don't think a pre-processing is necessary. You may find the Hough transform useful in your case.
Since your image is big, it can be difficult to have a straight line due to the noise ...
- 31
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