Image Processing¶
Centroiders¶
Functions for centroiding images.
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aotools.image_processing.centroiders.
brightest_pixel
(img, threshold, **kwargs)[source]¶ Centroids using brightest Pixel Algorithm (A. G. Basden et al, MNRAS, 2011)
Finds the nPxlsth brightest pixel, subtracts that value from frame, sets anything below 0 to 0, and finally takes centroid.
Parameters: - img (ndarray) – 2d or greater rank array of imgs to centroid
- threshold (float) – Fraction of pixels to use for centroid
Returns: Array of centroid values
Return type: ndarray
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aotools.image_processing.centroiders.
centre_of_gravity
(img, threshold=0, min_threshold=0, **kwargs)[source]¶ Centroids an image, or an array of images. Centroids over the last 2 dimensions. Sets all values under “threshold*max_value” to zero before centroiding Origin at 0,0 index of img.
Parameters: - img (ndarray) – ([n, ]y, x) 2d or greater rank array of imgs to centroid
- threshold (float) – Percentage of max value under which pixels set to 0
Returns: Array of centroid values (2[, n])
Return type: ndarray
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aotools.image_processing.centroiders.
correlation_centroid
(im, ref, threshold=0.0, padding=1)[source]¶ Correlation Centroider, currently only works for 3d im shape. Performs a simple thresholded COM on the correlation.
Parameters: - im – sub-aperture images (t, y, x)
- ref – reference image (y, x)
- threshold – fractional threshold for COM (0=all pixels, 1=brightest pixel)
- padding – factor to zero-pad arrays in Fourier transforms
Returns: centroids of im (2, t), given in order x, y
Return type: ndarray
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aotools.image_processing.centroiders.
cross_correlate
(x, y, padding=1)[source]¶ 2D convolution using FFT, use to generate cross-correlations.
Parameters: - x (array) – subap image
- y (array) – reference image
- padding (int) – Factor to zero-pad arrays in Fourier transforms
Returns: cross-correlation of x and y
Return type: ndarray
Contrast¶
Functions for calculating the contrast of an image.
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aotools.image_processing.contrast.
image_contrast
(image)[source]¶ Calculates the ‘Michelson’ contrast.
- Uses a method by Michelson (Michelson, A. (1927). Studies in Optics. U. of Chicago Press.), to calculate the contrast ratio of an image. Uses the formula:
- (img_max - img_min)/(img_max + img_min)
Parameters: image (ndarray) – Image array Returns: Contrast value Return type: float
PSF Analysis¶
Functions for analysing PSFs.
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aotools.image_processing.psf.
azimuthal_average
(data)[source]¶ Measure the azimuthal average of a 2d array
Parameters: data (ndarray) – A 2-d array of data Returns: A 1-d vector of the azimuthal average Return type: ndarray
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aotools.image_processing.psf.
encircled_energy
(data, fraction=0.5, center=None, eeDiameter=True)[source]¶ Return the encircled energy diameter for a given fraction (default is ee50d). Can also return the encircled energy function. Translated and extended from YAO.
Parameters: - data – 2-d array
- fraction – energy fraction for diameter calculation default = 0.5
- center – default = center of image
- eeDiameter – toggle option for return. If False returns two vectors: (x, ee(x)) Default = True
Returns: Encircled energy diameter or 2 vectors: diameters and encircled energies