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Questions tagged [image-processing]

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39
votes
4answers
25k views

How is Gaussian Blur Implemented?

I've read that blur is done in real time graphics by doing it on one axis and then the other. I've done a bit of convolution in 1D in the past but I am not super comfortable with it, nor know what to ...
11
votes
0answers
236 views

Why does increasing simplex noise dimension wash it out?

I just tried using this approach to create a tiling 2d simplex noise function with Gustavson's java implementation. The result tiled, but the texture seemed muddy / washed out. I decided to compare ...
8
votes
2answers
2k views

What is bilateral upsampling?

I've worked with various interpolation algorithms including linear, cubic (and bilinear and bicubic), other bezier (and nurbs, etc) based interpolations, lagrange interpolation and some others, but I ...
8
votes
2answers
931 views

What's a proper way to clamp dither noise?

When reducing color depth and dithering with a 2 bit noise (with n=]0.5,1.5[ and output=floor(input*(2^bits-1) + n)), the ends of the value range (inputs 0.0 and 1.0) are noisy. It would be desirable ...
7
votes
3answers
299 views

Changing image so it would look like through colorful glasses

I am currently working on some simple pixel shader in HLSL. I send to shader texture and I want to make it more colorful (something like in the picture below). In the picture 1 there is original ...
7
votes
1answer
615 views

Seamless Textures

I understand how an artist would make seamless textures by hand, but how can a computer program automate that process? Software like PixPlant is capable of doing this, but I don't understand how it ...
7
votes
1answer
2k views

Detect in-focus regions of an image

Is there any strategy to detect the region of an image that is sharp and in-focus, in order to separate the out-of-focus background? I've tried using edge detection methods but without any success. ...
7
votes
2answers
557 views

Algorithms to Remove High Frequency Noise from Path Tracing

I have been working on my own renderer for a while, and I'm wondering if there's any way to remove the Monte Carlo noise from the rendered image, besides waiting for a long time for it to converge? ...
7
votes
3answers
275 views

How to denoise video?

Video noise is random and not correlated in time. I assume, the best method is using wavelet denoise in this case, right? If yes, how is wavelet denoise implemented for video? Is there something to ...
7
votes
1answer
959 views

Average intensity of an gray image

Suppose i have a 400*300 gray scale image.Now I want to scan each line horizontally and make the average of that line 128,such that the values get scaled as per their difference from mean(128) which ...
6
votes
2answers
862 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 ...
6
votes
1answer
171 views

Converting raster shape/blob into displacement map

I am a beginner in digital image processing and computer graphics. I would like to program a similar behavior than the Shadermap 3 normal editor (displacement layer more specifically). As shown in ...
6
votes
1answer
324 views

Image rescaling algorithm

Suppose I have to use bilinear interpolation to rescale image. I more or less understand how enlargement works in case of integer scale factor. But what to do with non-integer scale and especially ...
6
votes
2answers
2k views

Rotate image around its center

I'm struggling with a problem with image rotation. I'm using the idea of "Rotation by area mapping" in the following link: http://www.leptonica.com/rotation.html My c# codes are as follows. The idea ...
6
votes
1answer
628 views

Tone Mapping & Gamma Correction

I've been looking up this question on the internet for a while, and I haven't been very successful, so I decided I'll ask it here. Should I apply tone mapping before gamma correction, gamma correction ...
6
votes
1answer
156 views

What is the state-of-the-art on using computers to “clean-up” images?

TWO PART QUESTION - We've all seen the movies/TV shows where the police/feds/spies use computer software to take a grainy photo and do a "clean-up" to see a better picture and more details. I assume ...
5
votes
2answers
183 views

reducing image size increases file size?

When I download this image: then its total size is 341,0 kB. The image has a width of 2880 pixels and height of 1100 pixel and 1 X/Y resolution pixel/in. I opened the image with gimp and pressed ...
5
votes
1answer
981 views

Image rotation algorithm

I would like to rotate a raster image by an arbitrary angle. I don't really care for speed: the rotation should be of highest quality possible. Could someone please suggest a suitable algorithm? I'm ...
5
votes
1answer
488 views

Instagram's fade effect

What is the pixel-level explanation of the fade effect, that was first popularized by Instagram? I want to implement this effect programmatically—that is, I want to understand what this effect is ...
5
votes
1answer
89 views

Seamlessly transitioning between nearby environment maps

I'm wondering what is the best way to achieve an effect like here: https://matterport.com/try/ when the camera is traveling between points in space. Apart from simple color crossfade there seems to ...
5
votes
1answer
199 views

SVG opengl implementation - strokes overlap on transparency

I am trying to implement svg rendering by opengl using meshes. In paths with opacity less than 1, the color of overlapping strokes add up. But it should be like this the opengl calls are: ...
5
votes
1answer
72 views

DLT algorithm (4+ points) not working, what's missing?

I'm doing a direct implementation of DLT algorithm but I can't figure out why, at the end the matrix H I get doesn't (even remotely) produce x2 = H*x1 The algorithm is not that complicated so I can't ...
5
votes
2answers
114 views

Downscaling by skipping rows and columns – any example images?

I'm about to implement downscaling on a microcontroller. Source resolution is e.g. 720x576 (the 576i PAL resolution, other one possible: 480i, NTSC resolution), destination is 32x16. The goal is to ...
5
votes
1answer
636 views

Is it better to blur the input or output of an edge detection shader for noise reduction?

To reduce noise of edge detection the norm seems like it is to apply a blur. However, is it generally better to apply the blur to the input of the edge detection. The input in my case being the depth ...
5
votes
0answers
127 views

CrazyBump Shape Recognition

I've recently been using CrazyBump, and I think I'm starting to understand how it works. But I'm confused about what it calls Shape Recognition. According to this website, that feature attempts to add ...
4
votes
2answers
473 views

How to perform an image normalization after for example adding a constant to it?

I had some magical tasks to do on my lessons. I had to write an app which performs some operations: basic (adding, subtracting, multiplying a constant and a second image), geometric, filtering, ...
4
votes
1answer
107 views

Relationship between spatial frequency of an image and Aliasing

I was looking into measuring the amount of aliasing in an image. After reading through many papers and sites, I came to the conclusion that the best method to measure the amount of aliasing in an ...
4
votes
2answers
339 views

Making low discrepancy sequence noise textures, not LDS sample positions

When making sampling locations, there is a lot of information out there on how to do white noise sampling, uniform sampling, uniform+jittered sampling, low discrepancy sequence sampling (eg halton) ...
4
votes
2answers
486 views

How linear interpolation works between mipmaps?

Nearest interpolation between 2 texels mean to take the texel whose center is nearest to a given coordinate to draw or, in other words, the texel the coordinate is matching. Linear interpolation ...
4
votes
1answer
109 views

Why does an affine transform work only on three of the corners?

I am trying to use a linear transformation to straighten out the camera angle on this image: In other words, I want to transform the image into a head-on view of the whiteboard. I applied an affine ...
4
votes
1answer
58 views

How to shift color values of a single RGB channel

I’m a weaver and textile maker with no prior coding or programming experience. In researching and reading through posts on this and other message boards, I was able to find a lot of useful information,...
4
votes
1answer
190 views

What graphics techniques can be used to simulate a color nebula effect?

I've been playing around with more advanced graphics these days (beyond the basic 2D UI and image effects that the iOS platform offers), and I'm wanting to implement a visual effect similar to how iOS'...
4
votes
2answers
836 views

How enlarge parts of a video like snapchat lens filter

I writing the this video process app which requires the each video frame to be processed such that parts of the video are enlarged. As a reference, one of the snapchat lens filter enlarges the eyes of ...
4
votes
1answer
193 views

Creating depth map from a 2-D image?

My question is oriented towards the generation of depth map using any of the state of the art depth sensor. However, each of these method required the presence of an 3-D object in front of the sensor....
4
votes
1answer
115 views

How can I implement a complex sinusoidal function?

The following is the 2d complex sinusoidal function, $u_0$ and $v_0$ represent Fundamental Frequencies in $X$ and $Y$ directions respectively. How can I represent $j$ (imaginary number)? Edit: ...
4
votes
1answer
105 views

How to detect a screen in a photo

Is there a way to make a difference between a photo of an actual object and a photo of an object through a computer or smartphone screen. For example: how can I detect that the second image is taken ...
4
votes
1answer
172 views

Was Evans & Sutherland CT5 really created in 1981?

A few days ago I found a video on Twitter showing the Evans & Sutherland CT5 Flight Simulator system. It was labeled as 1981 footage and looked really amazing. The first time I saw similar 3D ...
4
votes
1answer
113 views

Image regeneration with nearest neighbor search

So what I would like to achieve is this: User submits Image 1 - this image is then broken down into X by X sized blocks User submits Image 2 - then the program/algorithm takes all the blocks ...
4
votes
1answer
45 views

can half of a picture be processed and viewed?

Lets say i have a picture. I send it to a server. While sending it to the server half way the upload gets canceled. Now the server has half or some of the picture. Now is there a way in which this ...
4
votes
0answers
129 views

Sinc interpolation and Ideal reconstruction example

I am trying to apply sinc interpolation on this data set. The patches in the left image is a snapshot of AutoCAD 3d faces. Lux values are calculated for centre of each patch that are in 0.3m x 0.3m ...
4
votes
0answers
66 views

Slope Based Texturing

On the main page for Allegorithmic's Bitmap2Material, it mentions that the software uses a Slope Based approach over a Luminance Based approach. What exactly does this mean?
4
votes
1answer
409 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....
4
votes
0answers
84 views

Recreating a font from a low-quality printout

I have a JPEG file with a 200 dpi scan of a sample printout from a badly maintained old drum printer. I was able to segment it and to collect all instances of each letter together, for example I ...
3
votes
1answer
175 views

Improved Laplacian smoothing of noisy surface meshes

I have a question regarding Laplacian Smoothing of meshes and in particular the paper "Improved Laplacian smoothing of noisy surface meshes" by J. Vollmer in the early 2000's. What is the reason for ...
3
votes
1answer
75 views

What kind of image processing was used in the Facebook “Celebrate Pride” filter?

I am trying to recreate a filter that Facebook released back in 2015 when gay marriage was legalized in the US. Unfortunately, that filter no longer works/exists so people are left with only knockoff ...
3
votes
1answer
65 views

Adding noise to gradient

I found this picture When you zoom in to any part of the image, the background looks a bit noisy/grainy. See pixels around "violent violet" label: I'm trying to understand how to achieve the same ...
3
votes
1answer
227 views

Why is the line from the camera to vanishing point parallel to the other parallel lines?

When trying to find the vanishing point of an image, why is it that the vector from the center of the camera to the vanishing point is parallel to the parallel lines of the image? What's the ...
3
votes
1answer
339 views

ping pong between same framebuffer two color attachments

In order to optimize I'm trying to set up a setup which ping pong between same framebuffer two color attachments to apply some postprocess effects. It seems to work (effects are applied) but ...
3
votes
0answers
32 views

Sub-pixel image registration using phase

Currently I'm trying to reproduce the result by the academic papers Sub-pixel Shift Estimation of Image based on the Least Squares Approximation in Phase Region by Fujimoto, Fujisawa and Ikehara (...
3
votes
1answer
86 views

How would I convert a picture of a slanted surface into a straight one? [duplicate]

Suppose I took a picture of a whiteboard at an angle. If I could detect where the corners of the whiteboard are, what algorithms and linear projections could I use to convert this slanted view into a "...