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rescribe.xyz/integral

Package integral

v0.6.0
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The latest major version is .

Published: Aug 4, 2020 | License: GPL3 | Module: rescribe.xyz/integral

Overview

integral is a package for processing integral images, aka summed area tables. These are structures which precompute the sum of pixels to the left and above each pixel, which can make several common image processing operations much faster.

A lot of image processing operations rely on many calculations of the sum or mean of a set of pixels. As these have been precalculated for an integral image, these calculations are much faster. Image.Sum() and Image.Mean() functions are provided by this package to take advantage of this.

Another common requirement is standard deviation over an area of an image. This can be calculated by creating an integral image and squared integral image (SqImage) for a base image, and passing them to the MeanStdDev() function provided.

Index

Examples

func MeanStdDev

func MeanStdDev(i Image, sq SqImage, r image.Rectangle) (float64, float64)

MeanStdDev calculates the mean and standard deviation of a section of an image, using the corresponding regular and square integral images.

Example

Code:

package main

import (
	"fmt"
	"image"
	"image/draw"
	"log"
	"os"
	"rescribe.xyz/integral"

	_ "image/png"
)

func main() {
	f, err := os.Open("testdata/in.png")
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()
	img, _, err := image.Decode(f)
	if err != nil {
		log.Fatal(err)
	}
	b := img.Bounds()
	in := integral.NewImage(b)
	sq := integral.NewSqImage(b)
	draw.Draw(in, b, img, b.Min, draw.Src)
	draw.Draw(sq, b, img, b.Min, draw.Src)
	mean, stddev := integral.MeanStdDev(*in, *sq, b)
	fmt.Printf("Mean: %f, Standard Deviation: %f\n", mean, stddev)
}
Mean: 54677.229042, Standard Deviation: 21643.721672

type Image

type Image [][]uint64

Image is an integral image

func NewImage

func NewImage(r image.Rectangle) *Image

NewImage returns a new integral image with the given bounds.

func (Image) At

func (i Image) At(x, y int) color.Color

func (Image) Bounds

func (i Image) Bounds() image.Rectangle

func (Image) ColorModel

func (i Image) ColorModel() color.Model

func (Image) Mean

func (i Image) Mean(r image.Rectangle) float64

Mean returns the average value of pixels in a section of an image

Example

Code:

package main

import (
	"fmt"
	"image"
	"image/draw"
	"log"
	"os"
	"rescribe.xyz/integral"

	_ "image/png"
)

func main() {
	f, err := os.Open("testdata/in.png")
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()
	img, _, err := image.Decode(f)
	if err != nil {
		log.Fatal(err)
	}
	b := img.Bounds()
	in := integral.NewImage(b)
	draw.Draw(in, b, img, b.Min, draw.Src)
	fmt.Printf("Mean: %f\n", in.Mean(b))
}
Mean: 54677.229042

func (Image) Set

func (i Image) Set(x, y int, c color.Color)

func (Image) Sum

func (i Image) Sum(r image.Rectangle) uint64

Sum returns the sum of all pixels in a section of an image

Example

Code:

package main

import (
	"fmt"
	"image"
	"image/draw"
	"log"
	"os"
	"rescribe.xyz/integral"

	_ "image/png"
)

func main() {
	f, err := os.Open("testdata/in.png")
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()
	img, _, err := image.Decode(f)
	if err != nil {
		log.Fatal(err)
	}
	b := img.Bounds()
	in := integral.NewImage(b)
	draw.Draw(in, b, img, b.Min, draw.Src)
	fmt.Printf("Sum: %d\n", in.Sum(b))
}
Sum: 601340165

type SqImage

type SqImage [][]uint64

SqImage is a Square integral image. A squared integral image is an integral image for which the square of each pixel is saved; this is useful for efficiently calculating Standard Deviation.

func NewSqImage

func NewSqImage(r image.Rectangle) *SqImage

NewSqImage returns a new squared integral image with the given bounds.

func (SqImage) At

func (i SqImage) At(x, y int) color.Color

func (SqImage) Bounds

func (i SqImage) Bounds() image.Rectangle

func (SqImage) ColorModel

func (i SqImage) ColorModel() color.Model

func (SqImage) Mean

func (i SqImage) Mean(r image.Rectangle) float64

Mean returns the average value of pixels in a section of an image

func (SqImage) Set

func (i SqImage) Set(x, y int, c color.Color)

func (SqImage) Sum

func (i SqImage) Sum(r image.Rectangle) uint64

Sum returns the sum of all pixels in a section of an image

Package Files

  • integral.go
Documentation was rendered with GOOS=linux and GOARCH=amd64.

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