Misc. ./apps ./doc ./platoforms typos

Found via `codespell -q 3 --skip="./3rdparty" -I ../opencv-whitelist.txt`
This commit is contained in:
luz.paz
2018-02-08 13:04:25 -05:00
parent 090ee46f4a
commit d47b1f3b70
54 changed files with 98 additions and 98 deletions

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@@ -82,7 +82,7 @@ Non-maximum Suppression.
It is several times faster than other existing corner detectors.
But it is not robust to high levels of noise. It is dependant on a threshold.
But it is not robust to high levels of noise. It is dependent on a threshold.
FAST Feature Detector in OpenCV
-------------------------------

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@@ -25,7 +25,7 @@ used.
Second param is boolean variable, crossCheck which is false by default. If it is true, Matcher
returns only those matches with value (i,j) such that i-th descriptor in set A has j-th descriptor
in set B as the best match and vice-versa. That is, the two features in both sets should match each
other. It provides consistant result, and is a good alternative to ratio test proposed by D.Lowe in
other. It provides consistent result, and is a good alternative to ratio test proposed by D.Lowe in
SIFT paper.
Once it is created, two important methods are *BFMatcher.match()* and *BFMatcher.knnMatch()*. First
@@ -164,7 +164,7 @@ Second dictionary is the SearchParams. It specifies the number of times the tree
should be recursively traversed. Higher values gives better precision, but also takes more time. If
you want to change the value, pass search_params = dict(checks=100).
With these informations, we are good to go.
With this information, we are good to go.
@code{.py}
import numpy as np
import cv2 as cv

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@@ -39,7 +39,7 @@ grayscale image. Then you specify number of corners you want to find. Then you s
level, which is a value between 0-1, which denotes the minimum quality of corner below which
everyone is rejected. Then we provide the minimum euclidean distance between corners detected.
With all these informations, the function finds corners in the image. All corners below quality
With all this information, the function finds corners in the image. All corners below quality
level are rejected. Then it sorts the remaining corners based on quality in the descending order.
Then function takes first strongest corner, throws away all the nearby corners in the range of
minimum distance and returns N strongest corners.

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@@ -35,7 +35,7 @@ different scale. It is OK with small corner. But to detect larger corners we nee
For this, scale-space filtering is used. In it, Laplacian of Gaussian is found for the image with
various \f$\sigma\f$ values. LoG acts as a blob detector which detects blobs in various sizes due to
change in \f$\sigma\f$. In short, \f$\sigma\f$ acts as a scaling parameter. For eg, in the above image,
gaussian kernel with low \f$\sigma\f$ gives high value for small corner while guassian kernel with high
gaussian kernel with low \f$\sigma\f$ gives high value for small corner while gaussian kernel with high
\f$\sigma\f$ fits well for larger corner. So, we can find the local maxima across the scale and space
which gives us a list of \f$(x,y,\sigma)\f$ values which means there is a potential keypoint at (x,y) at
\f$\sigma\f$ scale.
@@ -66,7 +66,7 @@ the intensity at this extrema is less than a threshold value (0.03 as per the pa
rejected. This threshold is called **contrastThreshold** in OpenCV
DoG has higher response for edges, so edges also need to be removed. For this, a concept similar to
Harris corner detector is used. They used a 2x2 Hessian matrix (H) to compute the pricipal
Harris corner detector is used. They used a 2x2 Hessian matrix (H) to compute the principal
curvature. We know from Harris corner detector that for edges, one eigen value is larger than the
other. So here they used a simple function,
@@ -79,7 +79,7 @@ points.
### 3. Orientation Assignment
Now an orientation is assigned to each keypoint to achieve invariance to image rotation. A
neigbourhood is taken around the keypoint location depending on the scale, and the gradient
neighbourhood is taken around the keypoint location depending on the scale, and the gradient
magnitude and direction is calculated in that region. An orientation histogram with 36 bins covering
360 degrees is created. (It is weighted by gradient magnitude and gaussian-weighted circular window
with \f$\sigma\f$ equal to 1.5 times the scale of keypoint. The highest peak in the histogram is taken
@@ -89,7 +89,7 @@ with same location and scale, but different directions. It contribute to stabili
### 4. Keypoint Descriptor
Now keypoint descriptor is created. A 16x16 neighbourhood around the keypoint is taken. It is
devided into 16 sub-blocks of 4x4 size. For each sub-block, 8 bin orientation histogram is created.
divided into 16 sub-blocks of 4x4 size. For each sub-block, 8 bin orientation histogram is created.
So a total of 128 bin values are available. It is represented as a vector to form keypoint
descriptor. In addition to this, several measures are taken to achieve robustness against
illumination changes, rotation etc.

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@@ -26,7 +26,7 @@ and location.
![image](images/surf_boxfilter.jpg)
For orientation assignment, SURF uses wavelet responses in horizontal and vertical direction for a
neighbourhood of size 6s. Adequate guassian weights are also applied to it. Then they are plotted in
neighbourhood of size 6s. Adequate gaussian weights are also applied to it. Then they are plotted in
a space as given in below image. The dominant orientation is estimated by calculating the sum of all
responses within a sliding orientation window of angle 60 degrees. Interesting thing is that,
wavelet response can be found out using integral images very easily at any scale. For many