Questions tagged [computer-vision]

Computer vision includes methods of processing, analyzing, images and high-dimensional data to form high level understanding and recognition of the scene or images.

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Any references for the trade-off between software and mechanics/optics in industrial machine vision systems?

I explain my question with a simplified example. I can design an industrial vision system for the automatic inspection of an item with these main requirements: the image of a good piece must be a ...
11
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1answer
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Are there preferred patterns for creating texture on objects to aid computer vision?

In the comment to this answer using a laser diode and diffraction grating to provide texture on a surface was suggested to aid in height calculations in a computer vision system. I believe the ...
11
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1answer
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Recover curves from noisy collection of points

Background: I'm trying to make a system that tracks a number of bubbles in a video I'm implementing the bubble detection in the single image case using the Circular Hough Transform. Due to occlusion, ...
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3answers
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Camera calibration/pin hole camera model and working out 3d position

I have a calibrated camera and have the intrinsic parameters. I also have the extrinsic parameters relative to a point (the world origin) on a planar surface in the real world. This point I have set ...
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1answer
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Adaptive Thresholding for liver segmentation using Matlab

I need to segment liver from an abdominal CT image using Adaptive Thresholding. But I get the entire foreground separated from the background alone. I need only the liver part of the foreground ...
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1answer
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Vehicle counting from a video

Disclaimer: I posted this question on StackOverFlow but learned that it is better suited here. I am a bit new to image processing so I'd like to ask you about finding the optimal solution for my ...
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2answers
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Segmentation of half transparent material, e.g. glass

I'm totally stuck on an issue regarding the segmentation of glassy objects. I need to get the object as precise as possible. My approaches were different. At first I tried to remove the background, so ...
10
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1answer
911 views

The Scale Space Theory Understanding

In the scale-space theory the scale-space representation of the signal $f(x), x = (x_1, ..., x_d)$, (in case of image $d = 2$) is given as: $L(x, y; t) = g(x, y; t) * f(x, y)$ where $g(x, y; t)$ is a ...
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1answer
361 views

Designing a feature vector for discriminating between different sonic waveforms

Consider the 4 following waveform signals: ...
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2answers
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Digital image moments in plain English

I'm studying OpenCV and, in computer vision and image processing, people speak of blobs, contours, connected regions, and I sometimes hear the phrase "image moments". I know of an article on ...
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Are there any computer vision algorithms specifically targeting depth images?

I've been looking into marker detection algorithms to use with a kinect based application, and the majority of the work I've been able to find is obviously focused on feature detection in 'normal' ...
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1answer
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difference between feature detector and descriptor?

I am new to feature detection and tracking. can anybody please explain in detail the difference between detector and descriptors. which among these are detectors and which are descriptors : Harris, ...
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Understanding SURF Features Calculation Process

So, I was reading the paper on SURF (Bay, Ess, Tuytelaars, Van Gool: Speeded-Up Robust Features (SURF)) and I can not comprehend this paragraph below: Due to the use of box filters and integral ...
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Surface detection

How would one segment large area's of gray (ranging from white to black) from an image ? (If you know this in opencv, you may answer by saying what you would do in opencv). For example given this ...
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iPhone iOS UIImage how to detect a “laser pointer” dot on a camera feed?

I got a tracked robot toy and I'm controlling it with an iPhone. The robot outputs a live camera feed of a known frame size and I'm displaying it on UIImage. I've added a laser pointer to the robot ...
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1answer
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Good features / algorithms for recognizing car-models in images

I have a question concerning object recognition, especially recognizing car-models! I am at the beginning of a work about identifying the same car-model in different images. At the moment I think one ...
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2answers
240 views

The Parameter Devil — How to set them when no validation against groundtruth is possible [closed]

Question: I want to kick up a discussion on how people set algorithmic parameters when no validation against groundtruth is possible (maybe because groundtruth just cannot be obtained or is very hard/...
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2answers
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Algorithms for detection of fingertips or nails

Can you give me some advices on what could be the best algorithm(s) to use for detection of fingertips/nails in image. First thing that crossed my mind was Viola - Jones. After rethinking I concluded ...
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2answers
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How to estimate octave and size for visual features positioned at Harris corners

I am currently working with and comparing the performance of several feature detectors provided by OpenCV as basis for visual feature matching. I am using SIFT descriptors. I have accomplished ...
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1answer
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What is the link between the homography computed over 2 images and the homography computed over the same images upside down?

With OpenCV, I compute the homography between, say, these two images: and Don't worry about the strange white form on the right side, it is due to the smartphone holder I use. The homography, given ...
9
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1answer
128 views

In computer stereo vision, what does it mean to “look in”?

In trying to understand this answer to my earlier question, can someone explain why it is important that the cameras are not in the same plane when the focal distance is large compared to the ...
9
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1answer
776 views

Removing Noise from Dental Radiography

I'm working on a project of applying Active Shape Model to locate tooth in dental radiograph. For those familiar with the technique, I'm currently trying to sample along normal vectors for each ...
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2answers
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How to measure a lung nodule in a CT Scan DICOM image?

In this question, I would like to focus on intensity value of the CT Scan. First, take a look at the image below: The upper image is the original image, while the lower image is the thresholded ...
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1answer
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Counting vechicles in an image

I have been trying to implement an algorithm for successfully counting cars in an image. I have tried implementing A Method for Vehicle Count in the Presence of Multiple-Vehicle Occlusions in Traffic ...
9
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1answer
605 views

Accurately measuring relative distance between a set of fiducials (Augmented reality application)

Let's say I have a set of 5 markers. I am trying to find the relative distances between each marker using an augmented reality framework such as ARToolkit. In my camera feed thee first 20 frames show ...
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0answers
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Help in Retraining a HOG Descriptor using SVMLight

I am currently trying to count cars using OpenCV 2.4.4 with a HOG descriptor. Because a model for car detection is not available in OpenCV, I am creating my own model using SVMLight and a dataset of ...
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5answers
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Auto Detection of Rotation Angle on Arbitrary Image with Orthogonal Features

I have a task at hand where I need to detect angle of an image like the following sample (part of microchip photograph). The image does contain orthogonal features, but they could have different size, ...
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3answers
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Is it possible to convert from 2D to 3D form?

I have captured car positions at different frames from the video. Suppose car's(e.g.left side car which is coming towards us in the images) centroid at video frame1 is P(x1,y1) and Q(x2,y2) at video ...
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2answers
721 views

Precision of Computer Vision algorithms

Let's say the task is to determine element position on image. First very important thing is correct detection of object then some algorithms of calculating position are used (for examble blob analysis)...
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1answer
381 views

The small red peak in the CIE standard observer

The human eye has 3 types of color cones: red, green and blue. Their spectral sensitivity peaks in short (S, 420–440 nm), middle (M, 530–540 nm), and long (L, 560–580 nm) wavelengths. See diagram ...
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3answers
382 views

Gesture recognition using only simple techniques

I'm following a computer vision course and I have this exercise: write a program that, given an hand image, it can recognize if the hand is open, closed, in a punch, or holding an "ok" posture, using ...
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1answer
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How to remove reflections from images?

I've been playing around with making images better and removing all the unwanted disturbances from it. I found out a major concern would be removing the unwanted reflections that might come. I've ...
8
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2answers
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What is the state-of-the-art method for dealing with illumination issues in background subtraction?

I have been struggling to find a well-cited approach to this. Essentially, I am experimenting with different background subtraction algorithms, but none seem to perform well when there are ...
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2answers
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Generate the Convolution Matrix of 2D Kernel for Convolution Shape of `same`

I want to find a convolution matrix for a certain 2D kernel $ H $. For example, for image Img of size $ m \times n $ , I want (in MATALB): ...
8
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1answer
98 views

How do I reconstruct a covered-over part of a regular pattern

I have a set of images which consist of a fairly regular pattern - essentially a set of roughly concentric distorted ellipses - with a small area (<1% of the total image area) obscured by a ...
8
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1answer
183 views

What are the state of the art methods for person segmentation and person pose identification

I know that HOG is pretty state of the art for person detection, but in its original form HOG is only a detection method, and I don't believe it is particularly fast either (there is a significant ...
8
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1answer
322 views

How do I numerically calculate a function from its noisy gradient?

I have the model $\ s(x,y)=x^2+y^2, 0 \leq x \leq 1, 0 \leq y \leq 1 $. Instead of observing the model directly I am observing the derivatives of the model + some noise (e): $\ p(x,y)=s_x+e, q(x,y)=...
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3answers
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Purpose of image feature detection and matching

I'm a new guy in image processing and computer vision, so this question might be stupid to you. I just learned some feature detection and description algorithms, such as Harris, Hessian, SIFT, SURF, ...
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1answer
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How Hessian feature detector works?

I know about Harris corner detector, and I understand the basic idea of its second moment matrix, $$M = \left[ \begin{array}{cc} I_x^2 & I_xI_y \\ I_xI_y & I_y^2 \end{array} \right]$$, edges ...
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2answers
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Object detection versus object recognition

I have a slight confusion differentiating between object recognition and object detection. Some people say object detection is a sub-topic of object recognition? Can someone clarify the the difference ...
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2answers
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How to fit an ellipse to 2D data

I'd like to find the "best" fit of an ellipse to contiguous, possibly concave shapes such as: What have I tried? I thought that one could assign the direction of the major and minor axes $\vec a, \...
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1answer
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Suggested Preprocessing methods for OCR on Circular Images

Hello this is my sample image I am going to do real time character detection on images like that. I've tried SURF, SIFT, MSER and template matching on original image without any preprocessing. I can ...
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1answer
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Image processing and the Fourier Transform

I am trying to understand how and why the fourier transform is used in image processing / computer vision. Below is what I have gathered so far. Would my understanding of it be correct? If not, could ...
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3answers
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count blood cells

How to count blood cells in opencv? The problem is that they stick together. The example picture : Maybe pairwise geometric histogram (Geometric Histograms) suitable for matching partial circle ...
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1answer
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Is it possible to hack camera calibration without having access to the camera?

Many times we have a stream of video to process without access to camera. Having access to camera matrix would be beneficial for various processing techniques. Is it possible to hack camera ...
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1answer
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Get histogram of edge lengths/orientations in an image using OpenCV

In the process of trying to estimate whether a ROI contains [Japanese] text, I need to get a rough count of edges, hopefully binned by length and/or orientation... I think this would give me strong-...
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1answer
190 views

Minimization of Essential matrix

A problem in computer vision and 3d reconstruction is getting the camera's intrinsics parameters. A common solution is to use an object in which one knows the measurements of the shape before hand, ...
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1answer
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Skel to infinity morphological operations on 3D volume

I have a 3D volume image that consists of 2D tomographic images. In MatLab, for 2D images, we can use bwmorph and call for 'skel' operation to infinity to get a pixel thick overall outline of the ...
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1answer
507 views

find a line go through the center mass and that line must be inside object area

I have an object (orange color object) and I know its centroid/center mass C. I want program to automatically find another point ( can be point 1, point 2, point 3 or point 4 and so on) such that the ...
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3answers
989 views

Different representations of images and their purpose

I'm doing a small overview of different image representations used in image processing and computer vision. For every representation, I would like to have (at least) the following information: the ...