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nfnt 3502bb8cd1 Merge branch 'NRGBA_support'		vor 10 Jahren
.travis.yml	7e2ce0a2ea Go >=1.1 is needed for this package.	vor 11 Jahren
LICENSE	fa6861a5fd Documentation updated	vor 13 Jahren
README.md	03c3eb7832 Mention optimized access for image.NRGBA, image.NRGBA64 in README.	vor 10 Jahren
converter.go	daa7cf45d3 Return NRGBA images.	vor 11 Jahren
converter_test.go	299762ed77 Add unit tests for converter.go	vor 11 Jahren
filters.go	0feec06645 Dst pixel coordinate fix	vor 11 Jahren
nearest.go	79dc2b616d Add functions for nearest-neighbor resize of NRGBA, NRGBA16.	vor 11 Jahren
nearest_test.go	eefd4737aa Optimize YCbCr image resize	vor 11 Jahren
resize.go	45c239597b Fix compile error.	vor 11 Jahren
resize_test.go	618f7ff07a Add test case for correct pixel coordinates after resize.	vor 11 Jahren
thumbnail.go	b744503c5c Add: thumbnail helper function	vor 12 Jahren
thumbnail_test.go	b744503c5c Add: thumbnail helper function	vor 12 Jahren
ycc.go	f03c78969b Fix YCC SubImage.	vor 11 Jahren
ycc_test.go	acea8646b2 Fix error in YCC PixOffset and SubImage.	vor 11 Jahren

Resize

Image resizing for the Go programming language with common interpolation methods.

Installation

$ go get github.com/nfnt/resize

It's that easy!

Usage

This package needs at least Go 1.1. Import package with

import "github.com/nfnt/resize"

The resize package provides 2 functions:

resize.Resize creates a scaled image with new dimensions (width, height) using the interpolation function interp. If either width or height is set to 0, it will be set to an aspect ratio preserving value.
resize.Thumbnail downscales an image preserving its aspect ratio to the maximum dimensions (maxWidth, maxHeight). It will return the original image if original sizes are smaller than the provided dimensions.

resize.Resize(width, height uint, img image.Image, interp resize.InterpolationFunction) image.Image
resize.Thumbnail(maxWidth, maxHeight uint, img image.Image, interp resize.InterpolationFunction) image.Image

The provided interpolation functions are (from fast to slow execution time)

NearestNeighbor: Nearest-neighbor interpolation
Bilinear: Bilinear interpolation
Bicubic: Bicubic interpolation
MitchellNetravali: Mitchell-Netravali interpolation
Lanczos2: Lanczos resampling with a=2
Lanczos3: Lanczos resampling with a=3

Which of these methods gives the best results depends on your use case.

Sample usage:

package main

import (
	"github.com/nfnt/resize"
	"image/jpeg"
	"log"
	"os"
)

func main() {
	// open "test.jpg"
	file, err := os.Open("test.jpg")
	if err != nil {
		log.Fatal(err)
	}

	// decode jpeg into image.Image
	img, err := jpeg.Decode(file)
	if err != nil {
		log.Fatal(err)
	}
	file.Close()

	// resize to width 1000 using Lanczos resampling
	// and preserve aspect ratio
	m := resize.Resize(1000, 0, img, resize.Lanczos3)

	out, err := os.Create("test_resized.jpg")
	if err != nil {
		log.Fatal(err)
	}
	defer out.Close()

	// write new image to file
	jpeg.Encode(out, m, nil)
}

Caveats

Optimized access routines are used for image.RGBA, image.NRGBA, image.RGBA64, image.NRGBA64, image.YCbCr, image.Gray, and image.Gray16 types. All other image types are accessed in a generic way that will result in slow processing speed.
JPEG images are stored in image.YCbCr. This image format stores data in a way that will decrease processing speed. A resize may be up to 2 times slower than with image.RGBA.

Downsizing Samples

Downsizing is not as simple as it might look like. Images have to be filtered before they are scaled down, otherwise aliasing might occur. Filtering is highly subjective: Applying too much will blur the whole image, too little will make aliasing become apparent. Resize tries to provide sane defaults that should suffice in most cases.