Image Filters
| Image Filters | |
| Functions | |
| gdImageScatter | |
| gdImageScatterColor | |
| gdImageScatterEx | |
| gdImagePixelate | |
| gdImageNegate | Invert an image |
| gdImageGrayScale | Convert an image to grayscale |
| gdImageBrightness | Change the brightness of an image |
| gdImageContrast | Change the contrast of an image |
| gdImageColor | Change channel values of an image |
| gdImageConvolution | Apply a convolution matrix to an image |
| gdImageSelectiveBlur | |
| gdImageEdgeDetectQuick | Edge detection of an image |
| gdImageGaussianBlur | gdImageGaussianBlur performs a Gaussian blur of radius 1 on the image. |
| gdImageEmboss | Emboss an image |
| gdImageMeanRemoval | Mean removal of an image |
| gdImageSmooth | Smooth an image |
| gdImageCopyGaussianBlurred | Return a copy of the source image src blurred according to the parameters using the Gaussian Blur algorithm. |
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
| src | The image. |
Returns
Non-zero on success, zero on failure.
gdImageContrast
int gdImageContrast( gdImagePtr src, double contrast )
Change the contrast of an image
Parameters
| src | The image. |
| contrast | The 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
| src | The image. |
| red | The value to add to the red channel of all pixels. |
| green | The value to add to the green channel of all pixels. |
| blue | The value to add to the blue channel of all pixels. |
| alpha | The 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
| src | The image. |
| filter | The 3x3 convolution matrix. |
| filter_div | The value to divide the convoluted channel values by. |
| offset | The value to add to the convoluted channel values. |
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
| im | The image to blur |
Returns
GD_TRUE (1) on success, GD_FALSE (0) on failure.
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
| src | the source image |
| radius | the blur radius (not diameter--range is 2*radius + 1) |
| sigma | the 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);