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Charlie Vieth acea8646b2 Fix error in YCC PixOffset and SubImage.		před 11 roky
.travis.yml	09f4012229 Add Travis integration	před 13 roky
LICENSE	fa6861a5fd Documentation updated	před 13 roky
README.md	be07665345 Update README.md	před 11 roky
converter.go	eefd4737aa Optimize YCbCr image resize	před 11 roky
converter_test.go	299762ed77 Add unit tests for converter.go	před 11 roky
filters.go	427b8d133e Optimized Nearest-Neighbor function - 2x faster	před 11 roky
nearest.go	eefd4737aa Optimize YCbCr image resize	před 11 roky
nearest_test.go	eefd4737aa Optimize YCbCr image resize	před 11 roky
resize.go	eefd4737aa Optimize YCbCr image resize	před 11 roky
resize_test.go	016a61cd31 Optimize data-locality for a huge increase in processing speed.	před 11 roky
thumbnail.go	b744503c5c Add: thumbnail helper function	před 12 roky
thumbnail_test.go	b744503c5c Add: thumbnail helper function	před 12 roky
ycc.go	acea8646b2 Fix error in YCC PixOffset and SubImage.	před 11 roky
ycc_test.go	acea8646b2 Fix error in YCC PixOffset and SubImage.	před 11 roky

Resize

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

Installation

$ go get github.com/nfnt/resize

It's that easy!

Usage

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.RGBA64, 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.