Questions tagged [filtering]

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1answer
52 views

What does filter mean in glint rendering and texture mapping?

I bumped into the flowing when reading paper. Can anyone help to explain what does filter means in glint rendering and texture mapping? Thanks a lot!
3
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1answer
40 views

Plotting pbrt-v3 Gaussian filter

I want to plot the Gaussian filter of pbrt-v4 with a radius $(100,100)$ and a standard deviation ($\sigma$) of $0.5$. I would expect something like this: When I plot the pbrt-v4 Gaussian filter with ...
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0answers
51 views

What denoising filter gives highest quality for indirect light image?

Some background of my scenario: I have two images of indirect radiance, both are from an animation. I will reproject an pixel from the previous frame to current frame, and I want to do comparisons ...
1
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1answer
77 views

Does film filter introduce bias in path tracing?

Does using box or gaussian filter introduce bias to the image when reconstructing the pixel? Bias does not seem to be talked in the Chapter 7.8 of PBRT
1
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1answer
200 views

How does the GPU know whether to magnify/minify?

Let me first state what I think I know and please correct me if I'm too inaccurate or plainly wrong. When you use a function like texture, you're requesting a texel value given a pair (u,v) of texture ...
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0answers
51 views

How to retrieve RGBA mask used to transform image1 into image2

Let image1 be: And RGBA mask be: (45, 78, 251, 102) Apply mask on top of ...
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0answers
79 views

Relation between camera sensor responsivity and image reconstruction filter associated with a pixel

Let $W_{\text e}$ denote the camera sensor responsivity (i.e. importance) and $h_j$ and $W_{\text e}^{(j)}$ denote the image reconstruction filter and sensor response associated with the $j$th pixel, ...
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0answers
36 views

Convolution of multiple gaussian filters with different sizes

What is the size of the final filter after implement convolution of multiple gaussian filters with different sizes?
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2answers
167 views

Properties of the image reconstruction filter in rendering

Let $f$ denote the measurement contribution function for paths of length $k\in\mathbb N$, i.e. $$f(x)=g(x_0\leftrightarrow x_1)W_{\text e}(x_1\to x_0)t_k(x_0,\ldots,x_k)L_{\text e}(x_k\to x_{k-1}),$$ ...
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0answers
332 views

What is the difference between post-/pre- sampling, aliasing, filtering and processing?

What is the difference between post-/pre- sampling, aliasing, filtering and processing? How do the terms post-/pre-aliasing, post-/pre-processing, post-/pre-sampling and post-/pre-filtering relate to ...
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0answers
29 views

Image contribution function and reconstruction using filters

So I've been reading Physicall Based Rendering which in section 16.4.3 defines the "image contribution function" to be the following $$I_j = \int_\Omega h_j(X)L(X)d\Omega$$ where the variables are ...
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0answers
384 views

Lanczos filter implementation issue

I tried to follow Nathan Reed post Antialiasing: To Splat Or Not to implement splat method. The image I am getting thorugh the Lanczos filter is very different than Nathan. I do not understand where ...
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0answers
65 views

Why don't discretization errors occur with compute-shaded kernel filters?

An efficient compute-shaded image filter would be emitted with (screenX / [kernel width], screenY / [kernel height], 1) groups and one kernel in each group, allowing texels to pass into groupshared ...
2
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1answer
185 views

Texture units parameters in OpenGL

I am writing a procedural terrain renderer for OpenGL. To shade the terrain I use multitexturing, that is 4 material textures and a blend map which distributes them across the terrain (encoded in RGBA)...
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2answers
344 views

Texture prefiltering for Linearly Transformed Cosines

I'm implementing Real-Time Polygonal-Light Shading with Linearly Transformed Cosines from Siggraph 2016. I'm stuck on the texture prefiltering (section 5.3). As I understand they use ...
5
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1answer
761 views

Kaiser windowed sinc filter for mip mapping

These older but informative article talks about how a Kaiser windowed sinc filter is a good way to generate mips. The Inner Product - Mipmapping - Part 1 | Jonathan Blow The Inner Product - ...
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0answers
74 views

Baked anisotropic filtering using spherical harmonics

I want to learn is it good or bad idea. Let's assume video RAM is not a problem. For source texture create a texture of texels: spherical functions. Spherical functions defined by small arrays of ...
3
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1answer
1k views

Unexpected results from Mitchell-Netravali

I recently implemented Mitchell-Netravali filtering in my path-tracer with 16x (4x4) temporal anti-aliasing. PBR's demonstration image shows it should give significantly better results than the box ...
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0answers
1k views

YUV (NV12) Chroma subsampling while converting from RGB image

I convert RGB input to YUV 420 semi-planar output using compute shader.Luma plane is straightforward as it maps 1:1 with RGB dimensions. As we know, NV12 packs Cb and Cr into one plane, which means ...
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1answer
1k views

Ray tracing - partial derivatives for texture lookup

I'm doing some ray tracing on GPU using a fragment shader... How can I calculate texture coordinates partial derivatives with respect to screen coordinates so I could perform filtered texture lookup ...
16
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1answer
4k views

How are mipmap levels computed in Metal?

My question is specifically in regards to Metal, since I don't know if the answer would change for another API. What I believe I understand so far is this: A mipmapped texture has precomputed "...
2
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1answer
190 views

What is a common approach to smooth structures in textures?

I have a screen-aligned texture resulting from multiple rendering passes. It looks about this: I want the edges to appear smoother than they do now (but still keep their characteristic shape). When ...
3
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1answer
2k views

How can I remove aliasing in an image without introducing blur?

I am trying to reduce aliasing in an image using some filters. I tried the Gaussian variant of filters to remove the said high frequency patterns in the image, but I feel it's a bit too much of a blur....
3
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2answers
414 views

Suggested image preprocessing before applying threshold

I am trying to vectorize the contours (skewed rectangle) of the TV in the following original image. My first step is applying threshold. Tried selection of threshold values based on what skimage has ...
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0answers
651 views

how to overcome tracking jitter

I'm working with a object tracking project. Steps: Preprocessing the image and achieve some candidates regions of interest. For each region, test if it is the target by ORB/BF. After the target ...
2
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0answers
131 views

Image Laplacian incomprehension

I am reading and trying to implement a research paper. It uses openGL to define which part of an image to use in order to reconstitute a big image composited of several images. In order to do so, I ...
5
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2answers
2k views

Pixel dispersion (dissolving) algorithms

This YouTube video of a flip-dot display (physical b/w pixels) shows the reverse of an effect that might be called dissolve or dispersion, i.e. a text emerges from noise by pixels moving in to form ...
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2answers
787 views

Help me grasp Anisotropic Filtering (AF)

Lately I've been reading about texture filtering, namely Nearest-neighbor filtering, Bilinear filtering, Trilinear filtering, Anisotropic filtering, MIP maps, RIP Maps and so on. From a high-level ...
1
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0answers
100 views

Why does this edge detect show different results for the same color combinations?

I'm researching highlighting accessible color contrast via filter operations. I have a test screenshot of SRGB hex values compared with WCAG's official contrast algorithm: I converted it to its ...
11
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1answer
996 views

Path tracer - multi layered materials and importance sampling

I'm currently trying to implement a Monte Carlo path tracer. I've done some research and it seems that a common approach to materials is to use a layered model. Something like this: When light hits ...
6
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0answers
892 views

OpenGL texelFetch causes black stripes

THE SHORT VERSION In my fragment shader I'm reading (using texelFetch) multiple times the same texel from a texture (created by another fragment shader) and write it to the output render buffer. ...
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0answers
51 views

Removing a darkened caption with text on it in an image

Alright so I'm a complete n00b at image processing so forgive me if my question sounds vague. I'll try to supplement it with what I have learnt until now and also a couple of images. See the caption ...
16
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2answers
2k views

Why use a tent filter in path tracing?

The 99 lines of C path tracer Smallpt renders a 2x2 subpixel grid for each pixel it intends to render and then does a tent filter to combine them. There is an interesting presentation explaining the ...
24
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1answer
3k views

Anti-aliasing / Filtering in Ray Tracing

In ray tracing / path tracing, one of the simplest way to anti-alias the image is to supersample the pixel values and average the results. IE. instead of shooting every sample through the center of ...