Questions tagged [image-processing]

The tag has no usage guidance.

Filter by
Sorted by
Tagged with
17
votes
3answers
36k views

What are the differences between computer vision and image processing?

What are the differences between computer vision and image processing? For example, in object recognition, what are the roles of computer vision and image processing?
13
votes
1answer
7k views

2D convolution: Flipping the kernel?

Why do we need to flip the kernel in 2D convolution in the first place? What's the benefit of this? So, why can't we leave it unflipped? http://www.songho.ca/dsp/convolution/convolution2d_example.html ...
12
votes
2answers
3k views

Why is the laplace transform not popular for image processing convolution?

Why is the laplace transform not popular for image processing convolution? Most textbooks only conver the Fourier transforms.
11
votes
1answer
560 views

How to detect sunshine on a photo

How would you algorithmically detect for any given photo whether the sun was shining when the picture was taken? Examples A sample from this webcam at a mountain top: Clearly the sun is shining. ...
11
votes
1answer
218 views

Google DeepDream Elaborated

I've seen a few questions on this site about Deep Dream, however none of them seem to actually speak as to what DeepDream is doing, specifically. As far as I've gathered, they seem to have changed the ...
10
votes
1answer
3k views

Deriving the Sobel equations from derivatives

Many sites give the Sobel operators as the convolution mask for smoothing an image. However, I haven't found a single site that describes how you can derive the operators from partial first ...
9
votes
1answer
227 views

Recognizing waterways in an aerial photo — polygons from edge detection images

I am trying to recognize waterways from aerial photographs (say from Google Maps). Local governments often have GIS data that says where the waterways (and roads, buildings etc) are, but the water ...
7
votes
3answers
9k views

Shannon's entropy for an image

Shannon's entropy [plog(1/p)] for an image is a probabilistic method for comparing two pixels or a group of pixels.Suppose an image with a matrix of 3x3 has pixel intensity values ...
7
votes
1answer
2k views

Computer vision: object detection with labels that are single coordinates

Are there papers in the literature that address the following object detection task ? The task can be described as follows: Given a set of images, the labels are just coordinates (x,y) that ...
6
votes
1answer
1k views

circle packing algorithm used by Percolator

I was admiring this rendition of the Mona Lisa from quasimondo's Flickr account. He says: Combining circle packing with data visualization. The pie charts show the distribution of the dominant ...
6
votes
2answers
799 views

What are all the differences between the Gibbs phenomenon artefects and JPEG artefacts?

I thought the Gibbs phenomenom is the result of Fourier analysis estimation (but was it Fourier Series estimation or can it also be Fourier Transform estimation?) JPEG uses the Discrete cosines ...
6
votes
1answer
3k views

Which algorithms are usable for heatmaps and what are their pros and cons

This is a cross post from Stack Overflow, and DSP at Stackexchange since I cannot really decide which part of Stackexchange is most fitting. If this is the wrong place please tell me and I'll remove ...
6
votes
2answers
48 views

Determining width of paths

I have an image, like the one below that has different paths. I want to be able to detect the thin parts of these paths and highlight them. What is the best way to go about this?
6
votes
1answer
215 views

Summed-area table for circular range queries

A summed-area table is a data structure and algorithm for quickly and efficiently generating the sum of values in a rectangular subset of a grid [Wikipedia]. Is there any algorithm for quickly and ...
6
votes
0answers
494 views

Space filling between random 2D lines

Note that I had asked this question in GIS forum, although it has gotten many up-votes, still has not received any answer. Hope you can break the silence, some collaboration :) Consider a region (...
5
votes
5answers
2k views

Where can a student learn image processing?

I am a student of computer science with interest in image processing. I have learned how to apply a few effects to images like making them grayscale, sketching them out of lines, etc. I would like ...
5
votes
1answer
391 views

Reconstructing a screen of permuted pixels

Reconstructing a screen of permuted pixels Summary Given a video with the pixel locations randomly permuted (once, for the entire video), can we (efficiently) reconstruct the original picture? Let: ...
5
votes
2answers
7k views

find the actual size of an object from pixel coordinates

I am quite new to vision and OpenCV, so forgive me if this is a stupid question but I have got really confused. My aim is to detect an object in an image and estimate its actual size. Assume for now ...
5
votes
1answer
285 views

Bilinear Interpolation

I am trying to implement bilinear interpolation as described in the paper Spatial Tranformer Networks by Jaderberg et. al (see link to paper). They describe bilinear interpolation in Equation 5 as: $$...
5
votes
1answer
930 views

How to calculate Huffman code length without generating the actual huffman code?

Given a vector of elements, how can I calculate the length of the Huffman codewords without generating the Huffman code itself? Using Matlab, I was able to compute the Huffman code and and get the ...
5
votes
1answer
253 views

Why is Scale Space Needed to Detect Scale Invariant Features?

I have been doing research on the SIFT (scale invariant feature transform) algorithm, and while I have repeatedly read that in order to detect image features that do not vary with respect to scales of ...
4
votes
4answers
3k views

How to generate stereo image pair from a stationary mono camera?

I have a stationary mono camera which captures a single image frame at some fps. Assume the camera is not allowed to move,how do i generate a stereo image pair of the acquired frame? Is there any ...
4
votes
1answer
2k views

What is the difference between luma and luminance?

I understand the following (correct me if I'm wrong): Statements Luma as the weighted sum of RGB gamma corrected components, but luminance is the weighted sum of RGB linear components. The gamma ...
4
votes
1answer
3k views

Why does a color video compress better than a black and white video?

It was asked in an exam why a color video compress better than a black and white (grayscale) video using MPEG but can't find anything explaining it. In other words, we would apparently get a better ...
4
votes
2answers
2k views

Object recognition - given an image, does it contain a particular 3D object of interest?

I have in mind a particular 3D object. Given an image taken by a camera, I want to check whether that image contains an instance of my object. For instance, let's say that the object is a bathroom ...
4
votes
1answer
719 views

How does a predictive coding aid in lossless compression?

I'm working on this lab where we need to apply a lossless predictive coding to an image before compressing it (with Huffman, or some other lossless compression algorithm). From the example seen ...
4
votes
4answers
932 views

Which algorithm for counting the occurrences of a certain pattern (spots) in an image?

The Problem : Finding the number of occurrences of a certain pattern (or shape) in an image. In my example, the problem is about finding the number of spots (in variety of sizes) in an image. See ...
4
votes
1answer
8k views

The Fundamental and Essential Matrix

Could someone, in plain english, explain the distinction between the fundamental matrix and the essential matrix in multi-view computer vision? How are they different, and how can each be used in ...
4
votes
1answer
1k views

Training and testing image sizes for classification in computer vision

When training a classifier for object detection using features extracted from images (eg HoG features), how important is it that the images used for training fed into the classifier in their natural ...
4
votes
2answers
890 views

Difference between HSI and YCbCr for pattern recognition by color

I am doing a project on face detection in C#. I want to find the skin area by using skin color segmentation. For that purpose, I have to extract the skin area. I know I can use HSI or YCbCr, but what ...
4
votes
1answer
483 views

Register images containing objects with varying distance to the cameras

I'm learning about using image registration to align two images, e.g., two photographs of the same scene taken from a slightly different location. What factors influence how well we can align the ...
4
votes
1answer
496 views

Efficient flood filling (seed filling)

I am referring to the algorithm that fills a white area of arbitrary shape in a binary digital image, starting from a given white pixel, using the Moore (8 neighbors) or Neumann (4 neighbors) ...
4
votes
1answer
221 views

perspective transformation of a grid

A perspective transformation of a point is defined as follows: $ x' = \frac{M_{11}x + M_{12}y +M_{13}}{M_{31}x + M_{32}y +M_{33}} $ $ y' = \frac{M_{21}x + M_{22}y +M_{23}}{M_{31}x + M_{32}y +M_{33}} ...
4
votes
1answer
33 views

Inverting radial distortion

I'm trying to understand the math behind correcting a radial distortion (caused by a lens), but I'm failing to have it explained in simple terms. I found several examples that proceed this way: a ...
4
votes
2answers
157 views

Mathmatical way to represent an image kernel?

How to represent the calculation in this image mathematically? For example: With the discrete convolution $(f * g)[n]\ \stackrel{\mathrm{}}{=}\ \sum_{m=-\infty}^\infty f[m]\, g[n - m]$ and Fourier ...
4
votes
0answers
63 views

Metrics for image/visual complexity in computer vision/graphics?

Could anyone kindly point me to revenant literature in computer vision/graphics that detail on metrics for image/visual complexity and how to regularize that? More specifically, I am trying to design ...
4
votes
0answers
356 views

Stereo images rectification and disparity: which algorithms?

I'm trying to figure out what are currently the two most efficent algorithms that permit, starting from a Left/Right pair of stereo images created using a traditional camera (so affected by some ...
3
votes
3answers
188 views

How center the eyes of human face at specific pixels?

I am facing a problem with processing some frontal facial images. I need to adjust the centers of the eyes (irises) to be at certain specific pixels in the image. In other words, i need to transform ...
3
votes
1answer
277 views

Rearrange pixels to maximize visually distinguishable pattern

I have a dataset full of 0s and 1s, and when I visualize it with t-SNE, which does dimensionality reduction. There is clearly some structure in it as shown below. Each color corresponds to a ...
3
votes
2answers
898 views

Extracting features for texture classification

I'm a beginner in the field of pattern recognition and computer vision. I'm working on a project right now to classify t-shirt patterns into three categories i.e. solids, stripes and checks. I have ...
3
votes
2answers
355 views

How do I apply patch sized features to larger images?

I've been trying to teach myself some machine learning, and I wanted to ask what seems a simple question, but I've not been able to find any resources that explain the next step. Let's say I am doing ...
3
votes
1answer
66 views

Hausdorff distance between two binary images according to distance maps

I want to compute the Hausdorff distance between two (very large) binary images X and Y, which is: $$H(X,Y) = \max\left\{\,h(X,Y), h(Y,X)\right\}\!$$ with $$h(X,Y) = \sup_{x \in X} \inf_{y \in Y} d(...
3
votes
1answer
624 views

Given a low resolution video, is it possible to create a higher resolution image

This question is purely theoretical as I've not been able to find anyone who's done such a thing, so my question is - is it possible, and if not why? Say you have a short video (CCTV) of a face, or ...
3
votes
1answer
76 views

What is a visual bag of words and how is it implemented?

I'm currently working on implementing a bag of visual words in Python. I get the general gist of how it works but I can't seem to find any sources that explain it in more detail to a level where I can ...
3
votes
2answers
572 views

Meaning of topological distance between 2 pixels

I came across the notion of topology and topological distance in the context of image processing several times (especially when it came to mathematical morphology). I looked for a not too abstract ...
3
votes
1answer
131 views

Multi object image segmentation methods

I want to survey the state-of-the-art in image segmentation. Is there a paper on how to segment multiple objects in an image? The segmentation papers I read, normally identify one of the many objects ...
3
votes
1answer
102 views

Environment requirement in training image dataset for classifier

I have a question about preparing the dataset of positive samples for a cascaded classifier that will be used for object detection. As positive samples, I have been given 3 sets of images: a set of ...
3
votes
1answer
681 views

Identifying an object in an image based on color (AI ?)

First off, I am not sure if this is the correct stackexchange site to ask this question on, so moderators can feel free to move it. I am working on an application that identifies an object in an ...
3
votes
1answer
149 views

Which Is a Better Way of Obtaining Scales, Gaussian Blur or Down Sampling?

In computer vision, scales are important when we carry out a scene analysis. Choosing different scales affect the result of the analysis. For example, if a face is relatively small in the scene, then ...
3
votes
1answer
285 views

Stroke Width Transform: Gradient Direction and Rays

I've been trying to implement this paper from Boris Epshtein, Eyal Ofek, and Yonatan Wexler, the pioneers of Stroke Width Transform . Having a simple image with random texts, that underwent gray ...