Golang教程的切片练习-如果使用索引和值迭代，则我的代码不起作用

I'm doing golang tutorial, and the very first exercise is giving me a headache.

The exercise in a nutshell wants me to dynamically create a array with dx*dy dimention.

This is my function that receives dx, dy and returns [dx][dy]uint8 array that works:

func Pic(dx, dy int) [][]uint8 {
    resultArray := make([][]uint8, dx, dx)
    for i := range resultArray {
        fmt.Println(resultArray[i])
        resultArray[i] = make([]uint8, dy, dy)
        fmt.Println(resultArray)
        for j := range resultArray[i] {
            if (i+j)%30 <= 15 {
                resultArray[i][j] = uint8(255)
            }
        }
    }
    return resultArray
}

However, this code which uses for i, v := range x does not work:

func Pic(dx, dy int) [][]uint8 {
    resultArray := make([][]uint8, dx, dx)
    for i, ithRow := range resultArray {
        ithRow = make([]uint8, dy, dy)
        for j := range ithRow {
            if (i+j)%30 <= 15 {
                ithRow[j] = uint8(255)
            }
        }
    }
    return resultArray
}

Does this not work because ithRow is a copy of resultArray[i], but not reference of it? If so, why is it not reference of it(like, what is the benefit or use case of making it copied)?