Module distort Methods

DistortImage() distorts an image using various distortion methods, by mapping color lookups of the source image to a new destination image usally of the same size as the source image, unless 'bestfit' is set to true.

If 'bestfit' is enabled, and distortion allows it, the destination image is adjusted to ensure the whole source 'image' will just fit within the final destination image, which will be sized and offset accordingly. Also in many cases the virtual offset of the source image will be taken into account in the mapping.

If the '-verbose' control option has been set print to standard error the equicelent '-fx' formula with coefficients for the function, if practical.

The format of the DistortImage() method is:

  Image *DistortImage(const Image *image,const DistortImageMethod method,
    const size_t number_arguments,const double *arguments,
    MagickBooleanType bestfit, ExceptionInfo *exception)

A description of each parameter follows:

image

the image to be distorted.

method

the method of image distortion.

ArcDistortion always ignores source image offset, and always 'bestfit' the destination image with the top left corner offset relative to the polar mapping center.

Affine, Perspective, and Bilinear, do least squares fitting of the distrotion when more than the minimum number of control point pairs are provided.

Perspective, and Bilinear, fall back to a Affine distortion when less than 4 control point pairs are provided. While Affine distortions let you use any number of control point pairs, that is Zero pairs is a No-Op (viewport only) distortion, one pair is a translation and two pairs of control points do a scale-rotate-translate, without any shearing.

number_arguments

the number of arguments given.

arguments

an array of floating point arguments for this method.

bestfit

Attempt to 'bestfit' the size of the resulting image. This also forces the resulting image to be a 'layered' virtual canvas image. Can be overridden using 'distort:viewport' setting.

exception

return any errors or warnings in this structure

Extra Controls from Image meta-data (artifacts)...

o "verbose" Output to stderr alternatives, internal coefficents, and FX equivalents for the distortion operation (if feasible). This forms an extra check of the distortion method, and allows users access to the internal constants IM calculates for the distortion.

o "distort:viewport" Directly set the output image canvas area and offest to use for the resulting image, rather than use the original images canvas, or a calculated 'bestfit' canvas.

o "distort:scale" Scale the size of the output canvas by this amount to provide a method of Zooming, and for super-sampling the results.

Other settings that can effect results include

o 'interpolate' For source image lookups (scale enlargements)

o 'filter' Set filter to use for area-resampling (scale shrinking). Set to 'point' to turn off and use 'interpolate' lookup instead

SparseColorImage(), given a set of coordinates, interpolates the colors found at those coordinates, across the whole image, using various methods.

The format of the SparseColorImage() method is:

  Image *SparseColorImage(const Image *image,const ChannelType channel,
    const SparseColorMethod method,const size_t number_arguments,
    const double *arguments,ExceptionInfo *exception)

A description of each parameter follows:

image

the image to be filled in.

channel

Specify which color values (in RGBKA sequence) are being set. This also determines the number of color_values in above.

method

the method to fill in the gradient between the control points.

The methods used for SparseColor() are often simular to methods used for DistortImage(), and even share the same code for determination of the function coefficents, though with more dimensions (or resulting values).

number_arguments

the number of arguments given.

arguments

array of floating point arguments for this method-- x,y,color_values-- with color_values given as normalized values.

exception

return any errors or warnings in this structure