Stack Overflow
Stack Overflow

Questions tagged [computer-vision]

Use this tag for questions related to Computer Vision -- any aspect of software that enables computers to perceive, understand and react to their environment using cameras. For questions related to image filtering and quantification, use the tag [image-processing] instead.

Computer vision enables images, or sequences of images, to be processed by a computer using algorithms. There are many aspects to computer vision, including mathematics, physics (especially optics), imaging hardware, , and .

Some basic techniques used in computer vision are:

  • Image acquisition
  • Pre-processing
  • Feature Extraction
  • Detection/Segmentation
  • High-Level processing
  • Decision making
15559 questions
111
votes
5 answers

How does one convert a grayscale image to RGB in OpenCV (Python)?

I'm learning image processing using OpenCV for a realtime application. I did some thresholding on an image and want to label the contours in green, but they aren't showing up in green because my image is in black and white. Early in the program I…
user391339
  • 8,355
  • 13
  • 58
  • 71
105
votes
3 answers

What is "semantic segmentation" compared to "segmentation" and "scene labeling"?

Is semantic segmentation just a Pleonasm or is there a difference between "semantic segmentation" and "segmentation"? Is there a difference to "scene labeling" or "scene parsing"? What is the difference between pixel-level and pixelwise…
Martin Thoma
  • 124,992
  • 159
  • 614
  • 958
103
votes
6 answers

Automatic contrast and brightness adjustment of a color photo of a sheet of paper with OpenCV

When photographing a sheet of paper (e.g. with phone camera), I get the following result (left image) (jpg download here). The desired result (processed manually with an image editing software) is on the right: I would like to process the original…
Basj
  • 41,386
  • 99
  • 383
  • 673
100
votes
4 answers

How do I choose between Tesseract and OpenCV?

I recently came across Tesseract and OpenCV. It looks like Tesseract is a full-fledged OCR engine and OpenCV can be used as a framework to create an OCR application/service. I tried using Tesseract on some of my images and its accuracy seems…
Legend
  • 113,822
  • 119
  • 272
  • 400
96
votes
7 answers

Combining Two Images with OpenCV

I'm trying to use OpenCV 2.1 to combine two images into one, with the two images placed adjacent to each other. In Python, I'm doing: import numpy as np, cv img1 = cv.LoadImage(fn1, 0) img2 = cv.LoadImage(fn2, 0) h1, w1 =…
Cerin
  • 60,957
  • 96
  • 316
  • 522
90
votes
4 answers

Batch Normalization in Convolutional Neural Network

I am newbie in convolutional neural networks and just have idea about feature maps and how convolution is done on images to extract features. I would be glad to know some details on applying batch normalisation in CNN. I read this paper…
akshata bhat
  • 1,103
  • 2
  • 9
  • 9
89
votes
6 answers

Viola-Jones' face detection claims 180k features

I've been implementing an adaptation of Viola-Jones' face detection algorithm. The technique relies upon placing a subframe of 24x24 pixels within an image, and subsequently placing rectangular features inside it in every position with every size…
Paul Lammertsma
  • 37,593
  • 16
  • 136
  • 187
85
votes
7 answers

How do I find Wally with Python?

Shamelessly jumping on the bandwagon :-) Inspired by How do I find Waldo with Mathematica and the followup How to find Waldo with R, as a new python user I'd love to see how this could be done. It seems that python would be better suited to this…
tdc
  • 8,219
  • 11
  • 41
  • 63
83
votes
5 answers

Image Processing: What are occlusions?

I'm developing an image processing project and I come across the word occlusion in many scientific papers, what do occlusions mean in the context of image processing? The dictionary is only giving a general definition. Can anyone describe them using…
HaggarTheHorrible
  • 7,083
  • 20
  • 70
  • 81
82
votes
4 answers

Instance Normalisation vs Batch normalisation

I understand that Batch Normalisation helps in faster training by turning the activation towards unit Gaussian distribution and thus tackling vanishing gradients problem. Batch norm acts is applied differently at training(use mean/var from each…
Ruppesh Nalwaya
  • 1,409
  • 2
  • 14
  • 22
81
votes
7 answers

Converting an OpenCV Image to Black and White

How do you convert a grayscale OpenCV image to black and white? I see a similar question has already been asked, but I'm using OpenCV 2.3, and the proposed solution no longer seems to work. I'm trying to convert a greyscale image to black and white,…
Cerin
  • 60,957
  • 96
  • 316
  • 522
78
votes
4 answers

Detect and visualize differences between two images with OpenCV Python

I have two images and would like to make it obvious where the differences are. I want to add color to the two images such that a user can clearly spot all the differences within a second or two. For example, here are two images with a few…
PlsWork
  • 1,958
  • 1
  • 19
  • 31
78
votes
3 answers

How to define the markers for Watershed in OpenCV?

I'm writing for Android with OpenCV. I'm segmenting an image similar to below using marker-controlled watershed, without the user manually marking the image. I'm planning to use the regional maxima as markers. minMaxLoc() would give me the value,…
Tru
  • 1,467
  • 5
  • 18
  • 27
72
votes
11 answers

How to recognize vehicle license / number plate (ANPR) from an image?

I have a web site that allows users to upload images of cars and I would like to put a privacy filter in place to detect registration plates on the vehicle and blur them. The blurring is not a problem but is there a library or component (open source…
Ryan O'Neill
  • 5,410
  • 4
  • 46
  • 69
69
votes
2 answers

How to verify the correctness of calibration of a webcam?

I am totally new to camera calibration techniques... I am using OpenCV chessboard technique... I am using a webcam from Quantum... Here are my observations and steps.. I have kept each chess square side = 3.5 cm. It is a 7 x 5 chessboard with 6 x 4…
rotating_image
  • 3,046
  • 4
  • 28
  • 46
1
2
3
…
99 100