Go Resizing Images

Question

I am using the Go resize package here: https://github.com/nfnt/resize

1. I am pulling an Image from S3, as such:

   image_data, err := mybucket.Get(key) // this gives me data []byte 

2. After that, I need to resize the image:

   new_image := resize.Resize(160, 0, original_image, resize.Lanczos3) // problem is that the original_image has to be of type image.Image 

3. Upload the image to my S3 bucket

   err : = mybucket.Put('newpath', new_image, 'image/jpg', 'aclstring') // problem is that new image needs to be data []byte 

How do I transform a data []byte to ---> image.Image and back to ----> data []byte?

Answer 1

Read http://golang.org/pkg/image

// you need the image package, and a format package for encoding/decoding import (     "bytes"     "image"     "image/jpeg" // if you don't need to use jpeg.Encode, use this line instead      // _ "image/jpeg"      "github.com/nfnt/resize"       )  // Decoding gives you an Image. // If you have an io.Reader already, you can give that to Decode  // without reading it into a []byte. image, _, err := image.Decode(bytes.NewReader(data)) // check err  newImage := resize.Resize(160, 0, original_image, resize.Lanczos3)  // Encode uses a Writer, use a Buffer if you need the raw []byte err = jpeg.Encode(someWriter, newImage, nil) // check err 

Answer 2

The OP is using a specific library/package, but I think that the issue of "Go Resizing Images" can be solved without that package.

You can resize de image using golang.org/x/image/draw:

input, _ := os.Open("your_image.png") defer input.Close()  output, _ := os.Create("your_image_resized.png") defer output.Close()  // Decode the image (from PNG to image.Image): src, _ := png.Decode(input)  // Set the expected size that you want: dst := image.NewRGBA(image.Rect(0, 0, src.Bounds().Max.X/2, src.Bounds().Max.Y/2))  // Resize: draw.NearestNeighbor.Scale(dst, dst.Rect, src, src.Bounds(), draw.Over, nil)  // Encode to `output`:       png.Encode(output, dst) 

In that case I choose draw.NearestNeighbor, because it's faster, but looks worse. but there's other methods, you can see on https://pkg.go.dev/golang.org/x/image/draw#pkg-variables:

• draw.NearestNeighbor
  NearestNeighbor is the nearest neighbor interpolator. It is very fast, but usually gives very low quality results. When scaling up, the result will look 'blocky'.

• draw.ApproxBiLinear
  ApproxBiLinear is a mixture of the nearest neighbor and bi-linear interpolators. It is fast, but usually gives medium quality results.

• draw.BiLinear
  BiLinear is the tent kernel. It is slow, but usually gives high quality results.

• draw.CatmullRom
  CatmullRom is the Catmull-Rom kernel. It is very slow, but usually gives very high quality results.