Questions tagged [filtering]

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Is there a quicker way to draw a symmetric, scale-invariant (declining color) gradient around an ellipse?

The goal is to generate a picture like this: A symmetric color gradient around an ellipse which is rotated by $\theta$, has $(x_\circ,y_\circ)$ as center and and major and an minor axis $a,b$. The ...
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1 vote
18 views

text-rendering: why alpha testing produces wavy edges. And why SDF solves that problem

My first question is almost identical this one. I originally became aware of this when reading Valve's paper on using Signed Distance Field (or SDF for short) as seen here: However, I would really ...
• 23
1 vote
130 views

How do I normalize all pixel values such that all pixel values are 'pulled towards' the mean?

Originally asked in Graphic Design site here (but I don't know how to 'move' a question to another site) Credit to this guy: Python Tutorials for Digital Humanities - I followed a lot of his ideas, ...
• 113
1 vote
89 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!
• 43
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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 ...
• 133
1 vote
64 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 ...
• 51
1 vote
144 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
• 51
1 vote
568 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 ...
57 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 ...
• 101
94 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, ...
• 203
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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?
245 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. $$f(x)=g(x_0\leftrightarrow x_1)W_{\text e}(x_1\to x_0)t_k(x_0,\ldots,x_k)L_{\text e}(x_k\to x_{k-1}),$$ ...
• 203
1 vote
494 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 ...
1 vote
36 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 ...
• 205
631 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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1 vote
70 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 ...
• 447
456 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)...
• 153
445 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 ...
• 596
1k 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 - ...
• 7,801
90 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 ...
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 ...
• 447
1 vote
2k 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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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 ...
• 377
5k 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 "...
• 413
233 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 ...
• 165
3k 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....
445 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 ...
• 131
786 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 ...
• 121
150 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 ...
• 141
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 ...
• 153
1k 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 vote
116 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 ...
• 111
1k 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 ...
• 113
1k 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. ...
• 313
1 vote
53 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 ...
• 111
3k 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 ...
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