How to Convert a Go image.Image to a []byte for Efficient Storage and Transmission?

Convert Image.Image to []byte in Go

When dealing with image processing in Go, you may need to convert between image.Image and []byte formats. This can be useful for storing images in a database, sending them over the wire, or performing various image operations.

In your specific case, you're attempting to resize an image using the resize package and then convert the modified new_image to a []byte array for upload to an S3 bucket. However, your code contains a critical problem highlighted below:

// reset format the image.Image to data []byte here
var send_S3 []byte
var byteWriter = bufio.NewWriter(send_S3)
// ...
err = jpeg.Encode(byteWriter, new_image, nil)

The issue is that you're using bufio.NewWriter to wrap a []byte slice, which is incorrect for your purpose. bufio.Writer is designed for streaming output to an I/O device, not for holding binary data in memory.

To resolve this, you should use a bytes.Buffer instead. bytes.Buffer provides an in-memory buffer that can be used to construct a []byte slice:

buf := new(bytes.Buffer)
err := jpeg.Encode(buf, new_image, nil)
send_S3 := buf.Bytes()

This code creates a bytes.Buffer object named buf and uses the jpeg.Encode function to write the resized image data into buf. The Bytes() method of buf then returns the raw byte array representing the encoded image.

With this modification, your code will correctly convert the new_image to a []byte array, allowing you to upload it to S3 successfully.

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