imaging

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README

Imaging

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Package imaging provides basic image processing functions (resize, rotate, crop, brightness/contrast adjustments, etc.).

All the image processing functions provided by the package accept any image type that implements image.Image interface as an input, and return a new image of *image.NRGBA type (32bit RGBA colors, non-premultiplied alpha).

Installation

go get -u github.com/godoes/imaging

Documentation

https://pkg.go.dev/github.com/godoes/imaging

Usage examples

A few usage examples can be found below. See the documentation for the full list of supported functions.

Image resizing
// Resize srcImage to size = 128x128px using the Lanczos filter.
dstImage128 := imaging.Resize(srcImage, 128, 128, imaging.Lanczos)

// Resize srcImage to width = 800px preserving the aspect ratio.
dstImage800 := imaging.Resize(srcImage, 800, 0, imaging.Lanczos)

// Scale down srcImage to fit the 800x600px bounding box.
dstImageFit := imaging.Fit(srcImage, 800, 600, imaging.Lanczos)

// Resize and crop the srcImage to fill the 100x100px area.
dstImageFill := imaging.Fill(srcImage, 100, 100, imaging.Center, imaging.Lanczos)

Imaging supports image resizing using various resampling filters. The most notable ones:

  • Lanczos - A high-quality resampling filter for photographic images yielding sharp results.
  • CatmullRom - A sharp cubic filter that is faster than Lanczos filter while providing similar results.
  • MitchellNetravali - A cubic filter that produces smoother results with less ringing artifacts than CatmullRom.
  • Linear - Bilinear resampling filter, produces smooth output. Faster than cubic filters.
  • Box - Simple and fast averaging filter appropriate for downscaling. When upscaling it's similar to NearestNeighbor.
  • NearestNeighbor - Fastest resampling filter, no antialiasing.

The full list of supported filters: NearestNeighbor, Box, Linear, Hermite, MitchellNetravali, CatmullRom, BSpline, Gaussian, Lanczos, Hann, Hamming, Blackman, Bartlett, Welch, Cosine. Custom filters can be created using ResampleFilter struct.

Resampling filters comparison

Original image:

srcImage

The same image resized from 600x400px to 150x100px using different resampling filters. From faster (lower quality) to slower (higher quality):

Filter Resize result
imaging.NearestNeighbor dstImage
imaging.Linear dstImage
imaging.CatmullRom dstImage
imaging.Lanczos dstImage
Gaussian Blur
dstImage := imaging.Blur(srcImage, 0.5)

Sigma parameter allows to control the strength of the blurring effect.

Original image Sigma = 0.5 Sigma = 1.5
srcImage dstImage dstImage
Sharpening
dstImage := imaging.Sharpen(srcImage, 0.5)

Sharpen uses gaussian function internally. Sigma parameter allows to control the strength of the sharpening effect.

Original image Sigma = 0.5 Sigma = 1.5
srcImage dstImage dstImage
Gamma correction
dstImage := imaging.AdjustGamma(srcImage, 0.75)
Original image Gamma = 0.75 Gamma = 1.25
srcImage dstImage dstImage
Contrast adjustment
dstImage := imaging.AdjustContrast(srcImage, 20)
Original image Contrast = 15 Contrast = -15
srcImage dstImage dstImage
Brightness adjustment
dstImage := imaging.AdjustBrightness(srcImage, 20)
Original image Brightness = 10 Brightness = -10
srcImage dstImage dstImage
Saturation adjustment
dstImage := imaging.AdjustSaturation(srcImage, 20)
Original image Saturation = 30 Saturation = -30
srcImage dstImage dstImage
Hue adjustment
dstImage := imaging.AdjustHue(srcImage, 20)
Original image Hue = 60 Hue = -60
srcImage dstImage dstImage

FAQ

Incorrect image orientation after processing (e.g. an image appears rotated after resizing)

Most probably, the given image contains the EXIF orientation tag. The standard image/* packages do not support loading and saving this kind of information. To fix the issue, try opening images with the AutoOrientation decode option. If this option is set to true, the image orientation is changed after decoding, according to the orientation tag (if present). Here's the example:

img, err := imaging.Open("test.jpg", imaging.AutoOrientation(true))
What's the difference between imaging and gift packages?

imaging is designed to be a lightweight and simple image manipulation package. It provides basic image processing functions and a few helper functions such as Open and Save. It consistently returns *image.NRGBA image type (8 bits per channel, RGBA).

gift supports more advanced image processing, for example, sRGB/Linear color space conversions. It also supports different output image types (e.g. 16 bits per channel) and provides easy-to-use API for chaining multiple processing steps together.

Example code

package main

import (
	"image"
	"image/color"
	"log"

	"github.com/godoes/imaging"
)

func main() {
	// Open a test image.
	src, err := imaging.Open("testdata/flowers.png")
	if err != nil {
		log.Fatalf("failed to open image: %v", err)
	}

	// Crop the original image to 300x300px size using the center anchor.
	src = imaging.CropAnchor(src, 300, 300, imaging.Center)

	// Resize the cropped image to width = 200px preserving the aspect ratio.
	src = imaging.Resize(src, 200, 0, imaging.Lanczos)

	// Create a blurred version of the image.
	img1 := imaging.Blur(src, 5)

	// Create a grayscale version of the image with higher contrast and sharpness.
	img2 := imaging.Grayscale(src)
	img2 = imaging.AdjustContrast(img2, 20)
	img2 = imaging.Sharpen(img2, 2)

	// Create an inverted version of the image.
	img3 := imaging.Invert(src)

	// Create an embossed version of the image using a convolution filter.
	img4 := imaging.Convolve3x3(
		src,
		[9]float64{
			-1, -1, 0,
			-1, 1, 1,
			0, 1, 1,
		},
		nil,
	)

	// Create a new image and paste the four produced images into it.
	dst := imaging.New(400, 400, color.NRGBA{0, 0, 0, 0})
	dst = imaging.Paste(dst, img1, image.Pt(0, 0))
	dst = imaging.Paste(dst, img2, image.Pt(0, 200))
	dst = imaging.Paste(dst, img3, image.Pt(200, 0))
	dst = imaging.Paste(dst, img4, image.Pt(200, 200))

	// Save the resulting image as JPEG.
	err = imaging.Save(dst, "testdata/out_example.jpg")
	if err != nil {
		log.Fatalf("failed to save image: %v", err)
	}
}

Output:

dstImage

Documentation

Overview

Package imaging provides basic image processing functions (resize, rotate, crop, brightness/contrast adjustments, etc.).

All the image processing functions provided by the package accept any image type that implements image.Image interface as an input, and return a new image of *image.NRGBA type (32bit RGBA colors, non-premultiplied alpha).

Example 
package main

import (
	"image"
	"image/color"
	"log"

	"github.com/godoes/imaging"
)

func main() {
	// Open a test image.
	src, err := imaging.Open("testdata/flowers.png")
	if err != nil {
		log.Fatalf("failed to open image: %v", err)
	}

	// Crop the original image to 300x300px size using the center anchor.
	src = imaging.CropAnchor(src, 300, 300, imaging.Center)

	// Resize the cropped image to width = 200px preserving the aspect ratio.
	src = imaging.Resize(src, 200, 0, imaging.Lanczos)

	// Create a blurred version of the image.
	img1 := imaging.Blur(src, 5)

	// Create a grayscale version of the image with higher contrast and sharpness.
	img2 := imaging.Grayscale(src)
	img2 = imaging.AdjustContrast(img2, 20)
	img2 = imaging.Sharpen(img2, 2)

	// Create an inverted version of the image.
	img3 := imaging.Invert(src)

	// Create an embossed version of the image using a convolution filter.
	img4 := imaging.Convolve3x3(
		src,
		[9]float64{
			-1, -1, 0,
			-1, 1, 1,
			0, 1, 1,
		},
		nil,
	)

	// Create a new image and paste the four produced images into it.
	dst := imaging.New(400, 400, color.NRGBA{0, 0, 0, 0})
	dst = imaging.Paste(dst, img1, image.Pt(0, 0))
	dst = imaging.Paste(dst, img2, image.Pt(0, 200))
	dst = imaging.Paste(dst, img3, image.Pt(200, 0))
	dst = imaging.Paste(dst, img4, image.Pt(200, 200))

	// Save the resulting image as JPEG.
	err = imaging.Save(dst, "testdata/out_example.jpg")
	if err != nil {
		log.Fatalf("failed to save image: %v", err)
	}
}

Output:

Index

Examples

Constants

This section is empty.

Variables

View Source 
var ErrUnsupportedFormat = errors.New("imaging: unsupported image format")

ErrUnsupportedFormat means the given image format is not supported.

Functions

func AdjustBrightness 

func AdjustBrightness(img image.Image, percentage float64) *image.NRGBA

AdjustBrightness changes the brightness of the image using the percentage parameter and returns the adjusted image. The percentage must be in range (-100, 100). The percentage = 0 gives the original image. The percentage = -100 gives solid black image. The percentage = 100 gives solid white image.

Examples: 

dstImage = imaging.AdjustBrightness(srcImage, -15) // Decrease image brightness by 15%.
dstImage = imaging.AdjustBrightness(srcImage, 10) // Increase image brightness by 10%.

func AdjustContrast 

func AdjustContrast(img image.Image, percentage float64) *image.NRGBA

AdjustContrast changes the contrast of the image using the percentage parameter and returns the adjusted image. The percentage must be in range (-100, 100). The percentage = 0 gives the original image. The percentage = -100 gives solid gray image.

Examples: 

dstImage = imaging.AdjustContrast(srcImage, -10) // Decrease image contrast by 10%.
dstImage = imaging.AdjustContrast(srcImage, 20) // Increase image contrast by 20%.

func AdjustFunc 

func AdjustFunc(img image.Image, fn func(c color.NRGBA) color.NRGBA) *image.NRGBA

AdjustFunc applies the fn function to each pixel of the img image and returns the adjusted image.

Example: 

dstImage = imaging.AdjustFunc(
	srcImage,
	func(c color.NRGBA) color.NRGBA {
		// Shift the red channel by 16.
		r := int(c.R) + 16
		if r > 255 {
			r = 255
		}
		return color.NRGBA{uint8(r), c.G, c.B, c.A}
	}
)

func AdjustGamma 

func AdjustGamma(img image.Image, gamma float64) *image.NRGBA

AdjustGamma performs a gamma correction on the image and returns the adjusted image. Gamma parameter must be positive. Gamma = 1.0 gives the original image. Gamma less than 1.0 darkens the image and gamma greater than 1.0 lightens it.

Example: 

dstImage = imaging.AdjustGamma(srcImage, 0.7)

func AdjustHue 

func AdjustHue(img image.Image, shift float64) *image.NRGBA

AdjustHue changes the hue of the image using the shift parameter (measured in degrees) and returns the adjusted image. The shift = 0 (or 360 / -360 / etc.) gives the original image. The shift = 180 (or -180) corresponds to a 180° degree rotation of the color wheel and thus gives the image with its hue inverted for each pixel.

Examples: 

dstImage = imaging.AdjustHue(srcImage, 90) // Shift Hue by 90°.
dstImage = imaging.AdjustHue(srcImage, -30) // Shift Hue by -30°.

func AdjustSaturation 

func AdjustSaturation(img image.Image, percentage float64) *image.NRGBA

AdjustSaturation changes the saturation of the image using the percentage parameter and returns the adjusted image. The percentage must be in the range (-100, 100). The percentage = 0 gives the original image. The percentage = 100 gives the image with the saturation value doubled for each pixel. The percentage = -100 gives the image with the saturation value zeroed for each pixel (grayscale).

Examples: 

dstImage = imaging.AdjustSaturation(srcImage, 25) // Increase image saturation by 25%.
dstImage = imaging.AdjustSaturation(srcImage, -10) // Decrease image saturation by 10%.

func AdjustSigmoid 

func AdjustSigmoid(img image.Image, midpoint, factor float64) *image.NRGBA

AdjustSigmoid changes the contrast of the image using a sigmoidal function and returns the adjusted image. It's a non-linear contrast change useful for photo adjustments as it preserves highlight and shadow detail. The midpoint parameter is the midpoint of contrast that must be between 0 and 1, typically 0.5. The factor parameter indicates how much to increase or decrease the contrast, typically in range (-10, 10). If the factor parameter is positive the image contrast is increased otherwise the contrast is decreased.

Examples: 

dstImage = imaging.AdjustSigmoid(srcImage, 0.5, 3.0) // Increase the contrast.
dstImage = imaging.AdjustSigmoid(srcImage, 0.5, -3.0) // Decrease the contrast.

func Blur 

func Blur(img image.Image, sigma float64) *image.NRGBA

Blur produces a blurred version of the image using a Gaussian function. Sigma parameter must be positive and indicates how much the image will be blurred.

Example: 

dstImage := imaging.Blur(srcImage, 3.5)

func Clone 

func Clone(img image.Image) *image.NRGBA

Clone returns a copy of the given image.

func Convolve3x3 

func Convolve3x3(img image.Image, kernel [9]float64, options *ConvolveOptions) *image.NRGBA

Convolve3x3 convolves the image with the specified 3x3 convolution kernel. Default parameters are used if a nil *ConvolveOptions is passed.

func Convolve5x5 

func Convolve5x5(img image.Image, kernel [25]float64, options *ConvolveOptions) *image.NRGBA

Convolve5x5 convolves the image with the specified 5x5 convolution kernel. Default parameters are used if a nil *ConvolveOptions is passed.

func Crop 

func Crop(img image.Image, rect image.Rectangle) *image.NRGBA

Crop cuts out a rectangular region with the specified bounds from the image and returns the cropped image.

func CropAnchor 

func CropAnchor(img image.Image, width, height int, anchor Anchor) *image.NRGBA

CropAnchor cuts out a rectangular region with the specified size from the image using the specified anchor point and returns the cropped image.

func CropCenter 

func CropCenter(img image.Image, width, height int) *image.NRGBA

CropCenter cuts out a rectangular region with the specified size from the center of the image and returns the cropped image.

func Decode 

func Decode(r io.Reader, opts ...DecodeOption) (image.Image, error)

Decode reads an image from r.

func Encode 

func Encode(w io.Writer, img image.Image, format Format, opts ...EncodeOption) error

Encode writes the image img to w in the specified format (JPEG, PNG, GIF, TIFF or BMP).

func Fill 

func Fill(img image.Image, width, height int, anchor Anchor, filter ResampleFilter) *image.NRGBA

Fill creates an image with the specified dimensions and fills it with the scaled source image. To achieve the correct aspect ratio without stretching, the source image will be cropped.

Example: 

dstImage := imaging.Fill(srcImage, 800, 600, imaging.Center, imaging.Lanczos)

func Fit 

func Fit(img image.Image, width, height int, filter ResampleFilter) *image.NRGBA

Fit scales down the image using the specified resample filter to fit the specified maximum width and height and returns the transformed image.

Example: 

dstImage := imaging.Fit(srcImage, 800, 600, imaging.Lanczos)

func FlipH 

func FlipH(img image.Image) *image.NRGBA

FlipH flips the image horizontally (from left to right) and returns the transformed image.

func FlipV 

func FlipV(img image.Image) *image.NRGBA

FlipV flips the image vertically (from top to bottom) and returns the transformed image.

func Grayscale 

func Grayscale(img image.Image) *image.NRGBA

Grayscale produces a grayscale version of the image.

func Histogram 

func Histogram(img image.Image) [256]float64

Histogram returns a normalized histogram of an image.

Resulting histogram is represented as an array of 256 floats, where histogram[i] is a probability of a pixel being of a particular luminance i.

func Invert 

func Invert(img image.Image) *image.NRGBA

Invert produces an inverted (negated) version of the image.

func New 

func New(width, height int, fillColor color.Color) *image.NRGBA

New creates a new image with the specified width and height, and fills it with the specified color.

func Open 

func Open(filename string, opts ...DecodeOption) (image.Image, error)

Open loads an image from file.

Examples: 

// Load an image from file.
img, err := imaging.Open("test.jpg")

// Load an image and transform it depending on the EXIF orientation tag (if present).
img, err := imaging.Open("test.jpg", imaging.AutoOrientation(true))

func Overlay 

func Overlay(background, img image.Image, pos image.Point, opacity float64) *image.NRGBA

Overlay draws the img image over the background image at given position and returns the combined image. Opacity parameter is the opacity of the img image layer, used to compose the images, it must be from 0.0 to 1.0.

Examples: 

// Draw spriteImage over backgroundImage at the given position (x=50, y=50).
dstImage := imaging.Overlay(backgroundImage, spriteImage, image.Pt(50, 50), 1.0)

// Blend two opaque images of the same size.
dstImage := imaging.Overlay(imageOne, imageTwo, image.Pt(0, 0), 0.5)

func OverlayCenter 

func OverlayCenter(background, img image.Image, opacity float64) *image.NRGBA

OverlayCenter overlays the img image to the center of the background image and returns the combined image. Opacity parameter is the opacity of the img image layer, used to compose the images, it must be from 0.0 to 1.0.

func Paste 

func Paste(background, img image.Image, pos image.Point) *image.NRGBA

Paste pastes the img image to the background image at the specified position and returns the combined image.

func PasteCenter 

func PasteCenter(background, img image.Image) *image.NRGBA

PasteCenter pastes the img image to the center of the background image and returns the combined image.

func Resize 

func Resize(img image.Image, width, height int, filter ResampleFilter) *image.NRGBA

Resize resizes the image to the specified width and height using the specified resampling filter and returns the transformed image. If one of width or height is 0, the image aspect ratio is preserved.

Example: 

dstImage := imaging.Resize(srcImage, 800, 600, imaging.Lanczos)

func Rotate 

func Rotate(img image.Image, angle float64, bgColor color.Color) *image.NRGBA

Rotate rotates an image by the given angle counter-clockwise . The angle parameter is the rotation angle in degrees. The bgColor parameter specifies the color of the uncovered zone after the rotation.

func Rotate180 

func Rotate180(img image.Image) *image.NRGBA

Rotate180 rotates the image 180 degrees counter-clockwise and returns the transformed image.

func Rotate270 

func Rotate270(img image.Image) *image.NRGBA

Rotate270 rotates the image 270 degrees counter-clockwise and returns the transformed image.

func Rotate90 

func Rotate90(img image.Image) *image.NRGBA

Rotate90 rotates the image 90 degrees counter-clockwise and returns the transformed image.

func Save 

func Save(img image.Image, filename string, opts ...EncodeOption) (err error)

Save saves the image to file with the specified filename. The format is determined from the filename extension: "jpg" (or "jpeg"), "png", "gif", "tif" (or "tiff") and "bmp" are supported.

Examples: 

// Save the image as PNG.
err := imaging.Save(img, "out.png")

// Save the image as JPEG with optional quality parameter set to 80.
err := imaging.Save(img, "out.jpg", imaging.JPEGQuality(80))

func SetMaxProcs 

func SetMaxProcs(value int)

SetMaxProcs limits the number of concurrent processing goroutines to the given value. A value <= 0 clears the limit.

func Sharpen 

func Sharpen(img image.Image, sigma float64) *image.NRGBA

Sharpen produces a sharpened version of the image. Sigma parameter must be positive and indicates how much the image will be sharpened.

Example: 

dstImage := imaging.Sharpen(srcImage, 3.5)

func Thumbnail 

func Thumbnail(img image.Image, width, height int, filter ResampleFilter) *image.NRGBA

Thumbnail scales the image up or down using the specified resample filter, crops it to the specified width and hight and returns the transformed image.

Example: 

dstImage := imaging.Thumbnail(srcImage, 100, 100, imaging.Lanczos)

func Transpose 

func Transpose(img image.Image) *image.NRGBA

Transpose flips the image horizontally and rotates 90 degrees counter-clockwise.

func Transverse 

func Transverse(img image.Image) *image.NRGBA

Transverse flips the image vertically and rotates 90 degrees counter-clockwise.

Types

type Anchor 

type Anchor int

Anchor is the anchor point for image alignment. 

const (
	Center Anchor = iota
	TopLeft
	Top
	TopRight
	Left
	Right
	BottomLeft
	Bottom
	BottomRight
)

Anchor point positions.

type ConvolveOptions 

type ConvolveOptions struct {
	// If Normalize is true the kernel is normalized before convolution.
	Normalize bool

	// If Abs is true the absolute value of each color channel is taken after convolution.
	Abs bool

	// Bias is added to each color channel value after convolution.
	Bias int
}

ConvolveOptions are convolution parameters.

type DecodeOption 

type DecodeOption func(*decodeConfig)

DecodeOption sets an optional parameter for the Decode and Open functions.

func AutoOrientation 

func AutoOrientation(enabled bool) DecodeOption

AutoOrientation returns a DecodeOption that sets the auto-orientation mode. If auto-orientation is enabled, the image will be transformed after decoding according to the EXIF orientation tag (if present). By default it's disabled.

type EncodeOption 

type EncodeOption func(*encodeConfig)

EncodeOption sets an optional parameter for the Encode and Save functions.

func GIFDrawer 

func GIFDrawer(drawer draw.Drawer) EncodeOption

GIFDrawer returns an EncodeOption that sets the drawer that is used to convert the source image to the desired palette of the GIF-encoded image.

func GIFNumColors 

func GIFNumColors(numColors int) EncodeOption

GIFNumColors returns an EncodeOption that sets the maximum number of colors used in the GIF-encoded image. It ranges from 1 to 256. Default is 256.

func GIFQuantizer 

func GIFQuantizer(quantizer draw.Quantizer) EncodeOption

GIFQuantizer returns an EncodeOption that sets the quantizer that is used to produce a palette of the GIF-encoded image.

func JPEGQuality 

func JPEGQuality(quality int) EncodeOption

JPEGQuality returns an EncodeOption that sets the output JPEG quality. Quality ranges from 1 to 100 inclusive, higher is better. Default is 95.

func PNGCompressionLevel 

func PNGCompressionLevel(level png.CompressionLevel) EncodeOption

PNGCompressionLevel returns an EncodeOption that sets the compression level of the PNG-encoded image. Default is png.DefaultCompression.

type Format 

type Format int

Format is an image file format. 

const (
	JPEG Format = iota
	PNG
	GIF
	TIFF
	BMP
)

Image file formats.

func FormatFromExtension 

func FormatFromExtension(ext string) (Format, error)

FormatFromExtension parses image format from filename extension: "jpg" (or "jpeg"), "png", "gif", "tif" (or "tiff") and "bmp" are supported.

func FormatFromFilename 

func FormatFromFilename(filename string) (Format, error)

FormatFromFilename parses image format from filename: "jpg" (or "jpeg"), "png", "gif", "tif" (or "tiff") and "bmp" are supported.

func (Format) String 

func (f Format) String() string

type ResampleFilter 

type ResampleFilter struct {
	Support float64
	Kernel  func(float64) float64
}

ResampleFilter specifies a resampling filter to be used for image resizing. 

General filter recommendations:

- Lanczos
	A high-quality resampling filter for photographic images yielding sharp results.

- CatmullRom
	A sharp cubic filter that is faster than Lanczos filter while providing similar results.

- MitchellNetravali
	A cubic filter that produces smoother results with less ringing artifacts than CatmullRom.

- Linear
	Bilinear resampling filter, produces a smooth output. Faster than cubic filters.

- Box
	Simple and fast averaging filter appropriate for downscaling.
	When upscaling it's similar to NearestNeighbor.

- NearestNeighbor
	Fastest resampling filter, no antialiasing.

var BSpline ResampleFilter

BSpline is a smooth cubic filter (BC-spline; B=1; C=0). 

var Bartlett ResampleFilter

Bartlett is a Bartlett-windowed sinc filter (3 lobes). 

var Blackman ResampleFilter

Blackman is a Blackman-windowed sinc filter (3 lobes). 

var Box ResampleFilter

Box filter (averaging pixels). 

var CatmullRom ResampleFilter

CatmullRom is a Catmull-Rom - sharp cubic filter (BC-spline; B=0; C=0.5). 

var Cosine ResampleFilter

Cosine is a Cosine-windowed sinc filter (3 lobes). 

var Gaussian ResampleFilter

Gaussian is a Gaussian blurring filter. 

var Hamming ResampleFilter

Hamming is a Hamming-windowed sinc filter (3 lobes). 

var Hann ResampleFilter

Hann is a Hann-windowed sinc filter (3 lobes). 

var Hermite ResampleFilter

Hermite cubic spline filter (BC-spline; B=0; C=0). 

var Lanczos ResampleFilter

Lanczos filter (3 lobes). 

var Linear ResampleFilter

Linear filter. 

var MitchellNetravali ResampleFilter

MitchellNetravali is Mitchell-Netravali cubic filter (BC-spline; B=1/3; C=1/3). 

var NearestNeighbor ResampleFilter

NearestNeighbor is a nearest-neighbor filter (no anti-aliasing). 

var Welch ResampleFilter

Welch is a Welch-windowed sinc filter (parabolic window, 3 lobes).

Source Files

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