# Tag Info

Accepted

### Why do we need 4 points for homography but 7/8 points for fundamental matrix calculation?

It is because in the case of fundamental matrix, each correspondence point relates to only one constraint(i.e it maps a point to a line in other image). Hence 8 correspondence points are required. ...
• 241

### Do we really need two cameras for 3D vision?

First of all, our brain does not only rely on our stereo visionary system to estimate the depth. There are many cues in a image scence for depth estimation, of which stereo, vision belongs to a sub-...
• 1,976

### Do we really need two cameras for 3D vision?

Basically, two cameras are not "really needed" for the traditional perception of 3D vision. Access to two types of slightly different images is a common method. They can have different points of view ...

### Do we really need two cameras for 3D vision?

If you move your head (or if the target objects move against each other and/or the far background), you get stereoscopic data over time. Perhaps using some sort of visual memory to compare scene data ...
• 35.4k

### Why do we need 4 points for homography but 7/8 points for fundamental matrix calculation?

consider the number of DOFs and number of constraints. On the one hand, the matrix H contains 9 entries, but is defined only up to scale. Thus, the total number ...
• 143

### What is the difference between a range image and a depth map?

Your understanding is correct, it's z-values vs distances. A depth map contains the distances of points in the scene to a plane. A range image contains the distances of points in the scene to ...
• 121

### Do we really need two cameras for 3D vision?

Before going in to the details about 'why we need two cameras' part, the reason you can observe a 3D environment even with one eye is because even while using one eye, without any conscious effort due ...
• 168
Accepted

### Converting cutoff_frequency_ratio to Cycles/Pixel in Butterworth Filtering with skimage

How can I convert cutoff_frequency_ratio to "cycles per pixel"? They are the same thing. By expressing the cut off in terms of the ratio, the physical units, whether they were samples per ...
Accepted

### Clarification of some known issues in monocular visual odometry

There is only one "ambiguity": world scale is unknown. As you note, given a monocular image sequence observed from a calibrated camera (that is, with known intrinsic parameters), it is ...
1 vote

### What's the difference between SIFT and general stereo matching algorithm (eg, sgbm)?

After weeks of reading, researching and experiments, now I have more knowledge to answer my own question. Both of SIFT and SGBM can be used to find matching points but they are very different in the ...
• 213
1 vote

### Why are 8 points needed to compute a fundamental matrix?

They can. As Francesco mentioned, these problems can be solved with less correspondences. What makes the difference is how we formulate the problem. If we like a fast linear solution, then 8-points ...
• 5,465
1 vote

### Why are 8 points needed to compute a fundamental matrix?

Hum, no A homography can be exactly fit to 4 point such that no three of them are collinear (example implementation in OpenCv). An essential matrix can be fit to the image of 5 non-coplanar points (...
1 vote

### Is it possible to generate depth map from graycode sequence without using printed calibration patterns?

... if the camera's intrinsics are known and calibrated, is it possible to generate the depthmap fully automatically through a graycode sequence without any manual calibration process ? Yes, provided ...
• 10.7k
1 vote

### Do we really need two cameras for 3D vision?

Humans use other clues to estimate depth, i.e. previous knowledge of the objects. However, strictly geometrically speaking, you cannot obtain depth from one single point of view. Think of it in simple ...
• 111
1 vote

### What Is the Purpose of Bundle Adjustment?

Bundle adjustment is generally required for a multiview setting, where the number of cameras is large. In such regime, it is hard to exactly calibrate all the cameras extrinsically. Therefore, we ...
• 5,465
1 vote

### Why are two cameras mounted in paralle in stereo application?

When you say cameras are parallel it only means that the center pixels are parallel. Every pixel has a different angle, and that refers to the overlapping regions you were talking about. Actually ...
• 471
1 vote

### Kalman filter for tracking obstacles

You might consider a particle filter. Here's a link to a paper I wrote about tracking objects in video using a particle filter. The great thing about these is that objects can be tracked through ...
• 628
1 vote

### Can I use standard computer vision techniques for images taken in the NIR spectral range?

if it is possible to employ standard stereo matching algorithms like block-matching to images taken in the NIR spectrum and if so would it be possible (of course depending on the conditions) to obtain ...
• 10.7k
1 vote

### Can I use standard computer vision techniques for images taken in the NIR spectral range?

I have a collection of 170 reflectance spectra of various "materials" (such as ripe brown banana and asphalt) attributed to Ron Gershon of Eastman Kodak. I believe they are diffuse reflectance, which ...
• 13.5k
1 vote

### Can I use standard computer vision techniques for images taken in the NIR spectral range?

As far as I know, it is a common practice to use regular image processing techniques in this field. In fact I have recently finished a project in this field. if it is possible to employ standard ...
• 1,976
1 vote

### What is the difference between a range image and a depth map?

Range Image: Distances of points to another point, mapped on to a sphere (x,y,z). Range images are for x,y and z dimensions. As I understand, z is relative to a global point coordinate (as are x and ...
• 111

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