#include <cpl.h>

Functions
cpl_image *	clipm_priv_image_lineartrans_bilinear (const cpl_image input, const cpl_matrix transform, cpl_matrix shift, const cpl_size window_xxyy[4], int adjust_size, int use_outside_wdw, int norm_flag, int set_bpm_flag, cpl_image *contrib_map)
	Linearly transform a 2d-image using bilinear interpolation. More...

cpl_image *	clipm_priv_image_resample_bilinear (const cpl_image *input, double scale)
	Resample an image using bilinear interpolation. More...

double	clipm_priv_image_resample_undo_position (double resampled_position, double scale)
	Backtransform a position (x or y) from a resampled image to the original position before resampling (FITS convention). More...

double	clipm_priv_image_resample_position (double original_position, double scale)
	Transform a position (x or y) from an image, which is to be resampled, to the new position in the resampled image (FITS convention). More...

Function Documentation

cpl_image* clipm_priv_image_lineartrans_bilinear	(	const cpl_image *	input,
		const cpl_matrix *	transform,
		cpl_matrix *	shift,
		const cpl_size	window_xxyy[4],
		int	adjust_size,
		int	use_outside_wdw,
		int	norm_flag,
		int	set_bpm_flag,
		cpl_image **	contrib_map
	)

Linearly transform a 2d-image using bilinear interpolation.

Parameters

input	Input image
transform	2x2 transformation matrix
shift	2x1 shift matrix, will be modified if adjust_size is true (see below)
window_xxyy	Coordinate buffer of the form {xa, xb, ya, yb}, can be NULL, minimum/maximum order is irrelevant
adjust_size	Flag to allow resizing the output
use_outside_wdw	Flag to use also data outside window_xxyy (if not NULL), only used if adjust_size is true (see below)
norm_flag	Flag whether to already normalize the output image by the contribution weight, should default to 1 if contrib_map is not used, otherwise 0 if the contrib_map will be applied individually
set_bpm_flag	Flag whether to mark output pixels with a contribution of 0 as bad
contrib_map	(Optional output) image containing the weighting of each pixel during the interpolation, the range is [0...1], reflecting the influence of bad pixels or image borders

Principle:

This function performs a simple interpolation. This means, that a position in the output image is backtransformed, and the 4 surrounding pixels of this backtransformed position in the input image contribute to the interpolation.
This implicates, that with strong downscaling, not all input pixels might contribute. Therefore it is advisable in this case, to use clipm_priv_image_resample_bilinear() for downscaling first, and then this function for other transformations. The reason why this is not compensated is, that a free transformation might imply downscaling in one dimension and upscaling in the other, what results in unclear definition of the interpolation contribution in extreme cases.
If adjust_size is true, then
- the output image will be adjusted in its size to contain the full transformed image (window), and
- shift will be modified to reflect this new image content position (in this case it is not necessary to initialise shift with any value),
- if also use_outside_wdw is true, then also input data lying outside window_xxyy are used, which limits the function of window_xxyy to specify the corners that should define the output size.
If adjust_size is false, then
- extreme shift can lead to blank images, and
- use_outside_wdw is ignored.

Bad Pixel Handling:: Since bad pixels are marked with a zero weight in the optional contrib_map, the bad pixel map of the output image is really ONLY created if set_bpm_flag is true.

Error Handling:

The following errors may occur:

CPL_ERROR_NULL_INPUT: input, transform or shift is NULL
CPL_ERROR_ILLEGAL_INPUT:
- the size of transform is not 2x2
- the size of shift is not 2x1
CPL_ERROR_SINGULAR_MATRIX: transform is not invertible
CPL_ERROR_INVALID_TYPE: input is not of type CPL_TYPE_INT, CPL_TYPE_FLOAT, or CPL_TYPE_DOUBLE

cpl_image* clipm_priv_image_resample_bilinear	(	const cpl_image *	input,
		double	scale
	)

Resample an image using bilinear interpolation.

Parameters

input	The input image
scale	The scaling factor

Principle:

An image is resampled using bilinear sampling.
The new image will have the size s_new = floor(s_in * scale), where s represents x and y respectively.
The following coordinate transformation is applied (in FITS coordinates): x_new = scale*(x_old - 1/2) + 1/2
x_old = (1/ scale)*(x_new - 1/2) + 1/2,
and likewise with y.
The interpolation direction depends on the scale:
- with a scale >= 1, an output position is back-transformed, and the 4 surrounding input pixels contribute to the interpolation,
- with a scale < 1, an input position is transformed, and contributes to the 4 surrounding output pixels,
this way, always all input pixels are used.

Constraints:: The input image must be either of the type CPL_TYPE_FLOAT or CPL_TYPE_DOUBLE.

Error Handling:

The following error codes are set by this function:

CPL_ERROR_NULL_INPUT: input is NULL
CPL_ERROR_ILLEGAL_INPUT: scale <= 0
CPL_ERROR_INVALID_TYPE: input is neither of type CPL_TYPE_FLOAT nor CPL_TYPE_DOUBLE

double clipm_priv_image_resample_position	(	double	original_position,
		double	scale
	)

Transform a position (x or y) from an image, which is to be resampled, to the new position in the resampled image (FITS convention).

Parameters

original_position	The input position in the original image
scale	The scaling factor

Principle:

This function applies to the resampling method of clipm_priv_image_resample_bilinear().
scale must be greater 0.
The input parameters are not checked for validity.

double clipm_priv_image_resample_undo_position	(	double	resampled_position,
		double	scale
	)

Backtransform a position (x or y) from a resampled image to the original position before resampling (FITS convention).

Parameters

resampled_position	The position in the resampled image
scale	The scaling factor

Principle:

This function applies to the resampling method of clipm_priv_image_resample_bilinear().
scale must be greater 0.
The input parameters are not checked for validity.

Functions