How to change the resolution of an image?

Question

How do I change the resolution of this image before uploading?

f, uploadedFile, err := c.Request.FormFile("file") // image file
if err != nil {
    c.JSON(http.StatusInternalServerError, gin.H{
        "message": err.Error(),
        "error":   true,
    })
    return
}

fullcode: paste.ofcode.org/4wvAGNxZDmpqZ2Zucujmnw

Answer 1

As said icza you'll need an external lib to do that,
there is the basic : resize which is no longer maintained
and the bigger : imaging

In both case you'll need to get the standard image struct before using a resize lib.

that would look like something like this :

import(
"image"
github.com/disintegration/imaging
[...]
)
[...]

f, uploadedFile, err := c.Request.FormFile("file") // image file

// Decode the file into a image struct
var srcImg image.Image
srcImg, _, err = image.Decode(f)

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