"Fossies" - the Fresh Open Source Software Archive

Member "libgd-2.3.2/docs/naturaldocs/html/files/gd_filter-c.html" (5 Mar 2021, 47227 Bytes) of package /linux/www/libgd-2.3.2.tar.gz:


Caution: In this restricted "Fossies" environment the current HTML page may not be correctly presentated and may have some non-functional links. You can here alternatively try to browse the pure source code or just view or download the uninterpreted raw source code. If the rendering is insufficient you may try to find and view the page on the project site itself.

Image Filters

Summary
Image Filters
Functions
gdImageScatter
gdImageScatterColor
gdImageScatterEx
gdImagePixelate
gdImageNegateInvert an image
gdImageGrayScaleConvert an image to grayscale
gdImageBrightnessChange the brightness of an image
gdImageContrastChange the contrast of an image
gdImageColorChange channel values of an image
gdImageConvolutionApply a convolution matrix to an image
gdImageSelectiveBlur
gdImageEdgeDetectQuickEdge detection of an image
gdImageGaussianBlurgdImageGaussianBlur performs a Gaussian blur of radius 1 on the image.
gdImageEmbossEmboss an image
gdImageMeanRemovalMean removal of an image
gdImageSmoothSmooth an image
gdImageCopyGaussianBlurredReturn a copy of the source image src blurred according to the parameters using the Gaussian Blur algorithm.

Functions

gdImageScatter

int gdImageScatter(gdImagePtr im,
int sub,
int plus)

gdImageScatterColor

int gdImageScatterColor(gdImagePtr im,
int sub,
int plus,
int colors[],
unsigned int num_colors)

gdImageScatterEx

int gdImageScatterEx(gdImagePtr im,
gdScatterPtr scatter)

gdImagePixelate

int gdImagePixelate(gdImagePtr im,
int block_size,
const unsigned int mode)

gdImageNegate

int gdImageNegate(gdImagePtr src)

Invert an image

Parameters

srcThe image.

Returns

Non-zero on success, zero on failure.

gdImageGrayScale

int gdImageGrayScale(gdImagePtr src)

Convert an image to grayscale

The red, green and blue components of each pixel are replaced by their weighted sum using the same coefficients as the REC.601 luma (Y’) calculation.  The alpha components are retained.

For palette images the result may differ due to palette limitations.

Parameters

srcThe image.

Returns

Non-zero on success, zero on failure.

gdImageBrightness

int gdImageBrightness(gdImagePtr src,
int brightness)

Change the brightness of an image

Parameters

srcThe image.
brightnessThe value to add to the color channels of all pixels.

Returns

Non-zero on success, zero on failure.

See also

gdImageContrast

int gdImageContrast(gdImagePtr src,
double contrast)

Change the contrast of an image

Parameters

srcThe image.
contrastThe contrast adjustment value.  Negative values increase, postive values decrease the contrast.  The larger the absolute value, the stronger the effect.

Returns

Non-zero on success, zero on failure.

See also

gdImageColor

int gdImageColor(gdImagePtr src,
const int red,
const int green,
const int blue,
const int alpha)

Change channel values of an image

Parameters

srcThe image.
redThe value to add to the red channel of all pixels.
greenThe value to add to the green channel of all pixels.
blueThe value to add to the blue channel of all pixels.
alphaThe value to add to the alpha channel of all pixels.

Returns

Non-zero on success, zero on failure.

See also

gdImageConvolution

int gdImageConvolution(gdImagePtr src,
float filter[3][3],
float filter_div,
float offset)

Apply a convolution matrix to an image

Depending on the matrix a wide range of effects can be accomplished, e.g. blurring, sharpening, embossing and edge detection.

Parameters

srcThe image.
filterThe 3x3 convolution matrix.
filter_divThe value to divide the convoluted channel values by.
offsetThe value to add to the convoluted channel values.

Returns

Non-zero on success, zero on failure.

See also

gdImageSelectiveBlur

int gdImageSelectiveBlur(gdImagePtr src)

gdImageEdgeDetectQuick

int gdImageEdgeDetectQuick(gdImagePtr src)

Edge detection of an image

Parameters

srcThe image.

Returns

Non-zero on success, zero on failure.

See also

gdImageGaussianBlur

int gdImageGaussianBlur(gdImagePtr im)

gdImageGaussianBlur performs a Gaussian blur of radius 1 on the image.  The image is modified in place.

NOTE: You will almost certain want to use gdImageCopyGaussianBlurred instead, as it allows you to change your kernel size and sigma value.  Future versions of this function may fall back to calling it instead of gdImageConvolution, causing subtle changes so be warned.

Parameters

imThe image to blur

Returns

GD_TRUE (1) on success, GD_FALSE (0) on failure.

gdImageEmboss

int gdImageEmboss(gdImagePtr im)

Emboss an image

Parameters

imThe image.

Returns

Non-zero on success, zero on failure.

See also

gdImageMeanRemoval

int gdImageMeanRemoval(gdImagePtr im)

Mean removal of an image

Parameters

imThe image.

Returns

Non-zero on success, zero on failure.

See also

gdImageSmooth

int gdImageSmooth(gdImagePtr im,
float weight)

Smooth an image

Parameters

imThe image.
weightThe strength of the smoothing.

Returns

Non-zero on success, zero on failure.

See also

gdImageCopyGaussianBlurred

Return a copy of the source image src blurred according to the parameters using the Gaussian Blur algorithm.

radius is a radius, not a diameter so a radius of 2 (for example) will blur across a region 5 pixels across (2 to the center, 1 for the center itself and another 2 to the other edge).

sigma represents the “fatness” of the curve (lower == fatter).  If sigma is less than or equal to 0, gdImageCopyGaussianBlurred ignores it and instead computes an “optimal” value.  Be warned that future versions of this function may compute sigma differently.

The resulting image is always truecolor.

More Details

A Gaussian Blur is generated by replacing each pixel’s color values with the average of the surrounding pixels’ colors.  This region is a circle whose radius is given by argument radius.  Thus, a larger radius will yield a blurrier image.

This average is not a simple mean of the values.  Instead, values are weighted using the Gaussian function (roughly a bell curve centered around the destination pixel) giving it much more influence on the result than its neighbours.  Thus, a fatter curve will give the center pixel more weight and make the image less blurry; lower sigma values will yield flatter curves.

Currently, gdImageCopyGaussianBlurred computes the default sigma as

(2/3)*radius

Note, however that we reserve the right to change this if we find a better ratio.  If you absolutely need the current sigma value, you should set it yourself.

Parameters

srcthe source image
radiusthe blur radius (not diameter--range is 2*radius + 1)
sigmathe sigma value or a value <= 0.0 to use the computed default

Returns

The new image or NULL if an error occurred.  The result is always truecolor.

Example

FILE *in;
gdImagePtr result, src;

in = fopen("foo.png", "rb");
src = gdImageCreateFromPng(in);

result = gdImageCopyGaussianBlurred(im, src->sx / 10, -1.0);
int gdImageScatter(gdImagePtr im,
int sub,
int plus)
int gdImageScatterColor(gdImagePtr im,
int sub,
int plus,
int colors[],
unsigned int num_colors)
int gdImageScatterEx(gdImagePtr im,
gdScatterPtr scatter)
int gdImagePixelate(gdImagePtr im,
int block_size,
const unsigned int mode)
int gdImageNegate(gdImagePtr src)
Invert an image
int gdImageGrayScale(gdImagePtr src)
Convert an image to grayscale
int gdImageBrightness(gdImagePtr src,
int brightness)
Change the brightness of an image
int gdImageContrast(gdImagePtr src,
double contrast)
Change the contrast of an image
int gdImageColor(gdImagePtr src,
const int red,
const int green,
const int blue,
const int alpha)
Change channel values of an image
int gdImageConvolution(gdImagePtr src,
float filter[3][3],
float filter_div,
float offset)
Apply a convolution matrix to an image
int gdImageSelectiveBlur(gdImagePtr src)
int gdImageEdgeDetectQuick(gdImagePtr src)
Edge detection of an image
int gdImageGaussianBlur(gdImagePtr im)
gdImageGaussianBlur performs a Gaussian blur of radius 1 on the image.
int gdImageEmboss(gdImagePtr im)
Emboss an image
int gdImageMeanRemoval(gdImagePtr im)
Mean removal of an image
int gdImageSmooth(gdImagePtr im,
float weight)
Smooth an image
Return a copy of the source image src blurred according to the parameters using the Gaussian Blur algorithm.
Close