Hashers¶

All hashers from the Hasher class.

class perception.hashers.hasher.Hasher¶

All hashers implement a common set of methods from the Hasher base class.

allow_parallel = True¶: Indicates whether the hashes can be computed in parallel

compute_distance(hash1, hash2, hash_format='base64')¶

Compute the distance between two hashes.

Parameters:	hash1 (`Union`[`ndarray`, `str`]) – The first hash or vector hash2 (`Union`[`ndarray`, `str`]) – The second hash or vector hash_format – If either or both of the hashes are hash strings, what format the string is encoded in.

compute_parallel(filepaths, progress=None, progress_desc=None, max_workers=5, isometric=False)¶

Compute hashes in a parallelized fashion.

Parameters:	filepaths – A list of paths to images or videos (depending on the hasher). progress – A tqdm-like wrapper for reporting progress. If None, progress is not reported. progress_desc – The title of the progress bar. max_workers – The maximum number of workers isometric – Whether to compute all eight isometric transforms for each image.

distance_metric = None¶: The metric to use when computing distance between two hashes. All hashers must supply this parameter.

dtype = None¶: The numpy type to use when converting from string to array form. All hashers must supply this parameter.

hash_length = None¶: Indicates the length of the hash vector

returns_multiple = False¶: Whether or not this hash returns multiple values

string_to_vector(hash_string, hash_format='base64')¶

Convert hash string to vector.

Parameters:	hash_string (`str`) – The input hash string hash_format (`str`) – One of ‘base64’ or ‘hex’

vector_to_string(vector, hash_format='base64')¶

Convert vector to hash string.

Parameters:	vector (`ndarray`) – Input vector hash_format (`str`) – One of ‘base64’ or ‘hex’

Images¶

All image hashers inherit from the ImageHasher class.

class perception.hashers.hasher.ImageHasher¶

compute(image, hash_format='base64')¶

Compute a hash from an image.

Parameters:	image (`Union`[`str`, `ndarray`, `Image`, `BytesIO`]) – An image represented as a filepath, a PIL image object, or as an np.ndarray object. If it is an np.ndarray object, it must be in RGB color order (note the OpenCV default is BGR). hash_format – One ‘base64’, ‘hex’, or ‘vector’
Return type:	`Union`[`str`, `ndarray`]

compute_isometric_from_hash(hash_string_or_vector, hash_format='base64')¶

For supported hashes, obtain the hashes for the dihedral transformations of the original image. They are provided in the following order:

Vertical flip
Horizontal flip
180 degree rotation
90 degree rotation
90 degree rotation and vertical flip
90 degree rotation and horizontal flip
270 degree rotation

Parameters:	hash_string_or_vector – The hash string or vector hash_format – One ‘base64’ or ‘hex’

compute_with_quality(image, hash_format='base64')¶

Compute hash and hash quality from image.

Parameters:	image (`Union`[`str`, `ndarray`, `Image`, `BytesIO`]) – An image represented as a filepath, a PIL image object, or as an np.ndarray object. If it is an np.ndarray object, it must be in RGB color order (note the OpenCV default is BGR). hash_format – One ‘base64’ or ‘hex’
Return type:	`Tuple`[`str`, `int`]
Returns:	A tuple of (hash, quality)

The following image hash functions are included in the package.

class perception.hashers.image.AverageHash(hash_size=8)¶: Computes a simple hash comparing the intensity of each pixel in a resized version of the image to the mean. Implementation based on that of ImageHash.

class perception.hashers.image.PHash(hash_size=8, highfreq_factor=4, exclude_first_term=False, freq_shift=0)¶

Also known as the DCT hash, a hash based on discrete cosine transforms of images. See complete paper for details. Implementation based on that of ImageHash.

Parameters:	hash_size – The number of DCT elements to retain (the hash length will be hash_size * hash_size). highfreq_factor – The multiple of the hash size to resize the input image to before computing the DCT. exclude_first_term – WHether to exclude the first term of the DCT freq_shift – The number of DCT low frequency elements to skip.

class perception.hashers.image.WaveletHash(hash_size=8, image_scale=None, mode='haar')¶: Similar to PHash but using wavelets instead of DCT. Implementation based on that of ImageHash.

class perception.hashers.image.MarrHildreth¶: A wrapper around OpenCV’s Marr-Hildreth hash. See paper for details.

class perception.hashers.image.BlockMean¶: A wrapper around OpenCV’s Block Mean hash. See paper for details.

class perception.hashers.image.ColorMoment¶: A wrapper around OpenCV’s Color Moments hash. See paper for details.

class perception.hashers.image.PDQHash¶: The Facebook PDQ hash. Based on the original implementation located at the official repository.

class perception.hashers.image.DHash(hash_size=8)¶: A hash based on the differences between adjacent pixels. Implementation based on that of ImageHash.

class perception.hashers.image.PHashF(hash_size=8, highfreq_factor=4, exclude_first_term=False, freq_shift=0)¶: A real-valued version of PHash. It returns the raw 32-bit floats in the DCT. For a more compact approach, see PHashU8.

class perception.hashers.image.PDQHashF¶

class perception.hashers.image.PHashU8(hash_size=8, highfreq_factor=4, exclude_first_term=False, freq_shift=0)¶: A real-valued version of PHash. It uses minimum / maximum scaling to convert DCT values to unsigned 8-bit integers (more compact than the 32-bit floats used by PHashF at the cost of precision).

Videos¶

All video hashers inherit from the VideoHasher class.

class perception.hashers.hasher.VideoHasher¶

compute(filepath, errors='raise', hash_format='base64')¶

Compute a hash for a video at a given filepath.

Parameters:	filepath – Path to video file errors – One of “raise”, “ignore”, or “warn”. Passed to perception.hashers.tools.read_video.

hash_from_final_state(state)¶

Called after all frames have been processed. Returns the final feature vector.

Parameters:	state (`dict`) – The state dictionary at the end of processing.
Return type:	`ndarray`

process_frame(frame, frame_index, frame_timestamp, state=None)¶

Called for each frame in the video. For all but the first frame, a state is provided recording the state from the previous frame.

Parameters:	frame (`ndarray`) – The current frame as an RGB ndarray frame_index (`int`) – The current frame index frame_timestamp (`float`) – The current frame timestamp state (`Optional`[`dict`]) – The state from the last call to process_frame
Return type:	`dict`

The following video hash functions are included in the package.

class perception.hashers.video.FramewiseHasher(frame_hasher, interframe_threshold, frames_per_second=15, quality_threshold=None)¶

A hasher that simply returns frame-wise hashes at some regular interval with some minimum inter-frame distance threshold.

compute_batches(filepath, batch_size, errors='raise', hash_format='base64')¶

Compute hashes for a video in batches.

Parameters:	filepath (`str`) – Path to video file batch_size (`int`) – The batch size to use for returning hashes errors – One of “raise”, “ignore”, or “warn”. Passed to perception.hashers.tools.read_video. hash_format – The format in which to return hashes

hash_from_final_state(state)¶

Called after all frames have been processed. Returns the final feature vector.

Parameters:	state – The state dictionary at the end of processing.

process_frame(frame, frame_index, frame_timestamp, state=None)¶

Called for each frame in the video. For all but the first frame, a state is provided recording the state from the previous frame.

Parameters:	frame – The current frame as an RGB ndarray frame_index – The current frame index frame_timestamp – The current frame timestamp state – The state from the last call to process_frame

class perception.hashers.video.TMKL1(frame_hasher=None, frames_per_second=15, dtype='float32', distance_metric='cosine', norm=2, quality_threshold=None)¶

The TMK L1 video hashing algorithm.

hash_from_final_state(state)¶

Called after all frames have been processed. Returns the final feature vector.

Parameters:	state – The state dictionary at the end of processing.

process_frame(frame, frame_index, frame_timestamp, state=None)¶

Called for each frame in the video. For all but the first frame, a state is provided recording the state from the previous frame.

Parameters:	frame – The current frame as an RGB ndarray frame_index – The current frame index frame_timestamp – The current frame timestamp state – The state from the last call to process_frame

class perception.hashers.video.TMKL2(frame_hasher=None, frames_per_second=15, normalization='matrix')¶

The TMK L2 video hashing algorithm.

hash_from_final_state(state)¶

Called after all frames have been processed. Returns the final feature vector.

Parameters:	state – The state dictionary at the end of processing.

process_frame(frame, frame_index, frame_timestamp, state=None)¶

Called for each frame in the video. For all but the first frame, a state is provided recording the state from the previous frame.

Parameters:	frame – The current frame as an RGB ndarray frame_index – The current frame index frame_timestamp – The current frame timestamp state – The state from the last call to process_frame

class perception.hashers.video.SimpleSceneDetection(base_hasher=None, interscene_threshold=None, min_frame_size=50, max_scene_length=None)¶

The SimpleSceneDetection hasher is a wrapper around other video hashers to create separate hashes for different scenes / shots in a video. It works by shrinking each frame, blurring it, and doing a simple delta with the previous frame. If they are different, this marks the start of a new scene. In addition, this wrapper will also remove letterboxing from videos by checking for solid black areas on the edges of the frame.

Parameters:

base_hasher (Optional[VideoHasher]) – The base video hasher to use for each scene.
interscene_threshold – The distance threshold between sequential scenes that new hashes must meet to be included (this is essentially for deduplication)
min_frame_size – The minimum frame size to use for computing hashes. This is relevant for letterbox detection as black frames will tend to be completely “cropped” and make the frame very small.
max_scene_length – The maximum length of a single scene.

compute_batches(filepath, errors='raise', hash_format='base64', batch_size=10)¶

Compute a hash for a video at a given filepath and yield hashes in a given batch size.

Parameters:	filepath – Path to video file errors – One of “raise”, “ignore”, or “warn”. Passed to perception.hashers.tools.read_video. hash_format – The hash format to use when returning hashes. batch_size – The minimum number of hashes to include in each batch.

hash_from_final_state(state)¶

Called after all frames have been processed. Returns the final feature vector.

Parameters:	state – The state dictionary at the end of processing.

process_frame(frame, frame_index, frame_timestamp, state=None, batch_mode=False)¶

Called for each frame in the video. For all but the first frame, a state is provided recording the state from the previous frame.

Parameters:	frame – The current frame as an RGB ndarray frame_index – The current frame index frame_timestamp – The current frame timestamp state – The state from the last call to process_frame

Tools¶

These utility functions are only used by the hashers but are documented here for completeness.

perception.hashers.tools.compute_md5(filepath)¶

Compute the md5 hash for a file at filepath.

Parameters:	filepath – The path to the file
Return type:	`str`

perception.hashers.tools.compute_quality(image)¶: Compute a quality metric, using the calculation proposed by Facebook for their PDQ hash algorithm.

perception.hashers.tools.compute_synchronized_video_hashes(filepath, hashers, framerates=None, hash_format='base64', use_queue=True)¶

Compute the video hashes for a group of hashers with synchronized frame processing wherever possible.

Parameters:	filepath (`str`) – Path to video file. hashers (`dict`) – A dictionary mapping hasher names to video hasher objects hash_format – The format in which to return the hashes use_queue – Whether to use queued video frames

perception.hashers.tools.get_common_framerates(id_rates)¶

Compute an optimal set of framerates for a list of framerates. Optimal here means that reading the video at each of the framerates will allow one to collect all of the frames required with the smallest possible number of frames decoded.

For example, consider if we need to read a video at 3 fps, 5 fps, 1 fps and 0.5 fps. We could read the video 4 times (once per framerate). But a more optimal approach is to read the video only twice, once at 3 frames per second and another time at 5 frames per second. For the 1 fps hasher, we simply pass every 3rd frame of the 3 fps pass. For the 0.5 fps hasher, we pass every 6th frame of the 3 fps pass. So if you pass this function {A: 3, B: 5, C: 1, D: 0.5}, you will get back {3: [A, C, D], 5: C}.

Parameters:	id_rates (`dict`) – A dictionary with IDs as keys and frame rates as values.
Returns:	A dictionary with framerates as keys and a list of ids as values.
Return type:	rate_ids

perception.hashers.tools.get_string_length(hash_length, dtype, hash_format='hex')¶

Compute the expected length of a hash string.

Parameters:	hash_length (`int`) – The length of the hash vector dtype (`str`) – The dtype of the vector hash_format – One of ‘base64’ or ‘hex’
Return type:	`int`
Returns:	The expected string length

perception.hashers.tools.read(filepath_or_buffer, timeout=None)¶

Read a file into an image object

Parameters:	filepath_or_buffer (`Union`[`str`, `ndarray`, `Image`, `BytesIO`]) – The path to the file or any object with a read method (such as io.BytesIO) timeout – If filepath_or_buffer is a URL, the timeout to use for making the HTTP request.

perception.hashers.tools.read_video(filepath, frames_per_second=None, max_queue_size=128, use_queue=True, errors='raise')¶

Provides a generator of RGB frames, frame indexes, and timestamps from a video. This function requires you to have installed ffmpeg.

Parameters:

filepath – Path to the video file
frames_per_second (Union[str, float, None]) – How many frames to provide for each second of video. If None, all frames are provided. If frames_per_second is “keyframes”, we use ffmpeg to select I frames from the video.
max_queue_size – The maximum number of frames to load in the queue
use_queue – Whether to use a queue of frames during processing
errors – Whether to ‘raise’, ‘warn’, or ‘ignore’ errors

Yields:

(frame, frame_index, timestamp) tuples

perception.hashers.tools.string_to_vector(hash_string, dtype, hash_length, hash_format, verify_length=True)¶

Convert hash back to vector.

Parameters:	hash_string (`str`) – The input base64 hash string dtype (`str`) – The data type of the hash hash_length (`int`) – The length of the hash vector verify_length (`bool`) – Whether to verify the string length

perception.hashers.tools.unletterbox(image)¶

Obtain bounds on an image that remove the black bars on the top, right, bottom, and left side of an image.

Parameters:	image – The image from which to remove letterboxing.
Return type:	`Optional`[`Tuple`[`Tuple`[`int`, `int`], `Tuple`[`int`, `int`]]]
Returns:	A pair of coordinates bounds of the form (x1, x2) and (y1, y2) representing the left, right, top, and bottom bounds.

perception.hashers.tools.vector_to_string(vector, dtype, hash_format)¶

Convert vector to hash.

Parameters:	vector (`ndarray`) – Input vector