# invariant hashing (caclulation of the hamming or the levenshtein distance when the image is flipped, rotated or cropped)

### Description

flip-rotate-crop an image and caclulate the hamming or the levenshtein distance for phash, average_hash, dhash

### Usage

1 2 3 | ```
invariant_hash(image, new_image, method = "phash", mode = "binary",
hash_size = 8, highfreq_factor = 4, resize = "nearest", flip = T,
rotate = T, angle_bidirectional = 10, crop = T)
``` |

### Arguments

`image` |
a 2-dimensional matrix or data frame (only gray-scale images are valid) |

`new_image` |
a new image to be compared with the previous input image |

`method` |
one of 'phash', 'average_hash', 'dhash' |

`mode` |
one of 'binary', 'hash' |

`hash_size` |
an integer specifying the hash size. IF method = 'phash' : the hash_size * highfreq_factor should be less than number of floor(rows * 0.8) or floor(columns * 0.8) of the gray_image IF method = 'dhash' or 'average_hash' : the hash_size should be less than number of floor(rows * 0.8) or floor(columns * 0.8) of the gray_image |

`highfreq_factor` |
an integer specyfing the highfrequency factor (IF method = 'phash' : the hash_size * highfreq_factor should be less than number of floor(rows * 0.8) or floor(columns * 0.8) of the gray_image) |

`resize` |
corresponds to one of 'nearest', 'bilinear' (resizing method) |

`flip` |
if TRUE the new_image will be flipped both horizontal and vertical |

`rotate` |
if TRUE the new_image will be rotated for a specified angle (see angle_bidirectional) |

`angle_bidirectional` |
a float specifying the angle that the images should be rotated in both directions. For instance, if angle_bidirectional = 10 then the image will be rotated for 10 and 350 (360-10) degrees. |

`crop` |
if TRUE the new_image will be cropped 10 or 20 percent (equally spaced horizontally and vertically) |

### Details

This function performs the following transformations : flips an image (no-flip, horizonal-flip, vertical-flip), rotates an image (no-angle, angle_bidirectional, 360-angle_bidirectional) and crops an image (no-crop, 10-percent-crop, 20-percent-crop). Depending on the type of mode ('binary', 'hash'), after each transformation the hamming or the levenshtein distance between the two images is calculated.

### Value

If flip, rotate and crop are all FALSE then the function returns either the hamming distance (if mode = 'binary') or the levenshtein distance (if mode = 'hash') for the two images. If any of the flip, rotate, crop is TRUE then it returns the MIN, MAX of the hamming distance (if mode = 'binary') or the MIN,MAX of the levenshtein distance (if mode = 'hash').

### Examples

1 2 3 4 5 6 7 8 9 10 11 | ```
path1 = system.file("tmp_images", "1.png", package = "OpenImageR")
path2 = system.file("tmp_images", "2.jpg", package = "OpenImageR")
image1 = rgb_2gray(readImage(path1))
image2 = rgb_2gray(readImage(path2))
res1 = invariant_hash(image1, image2, hash_size = 3, flip = TRUE, crop = FALSE)
res2 = invariant_hash(image1, image2, mode = 'hash', hash_size = 3, angle_bidirectional = 10)
``` |

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