func GetImageFromDatastore(w http.ResponseWriter, r *http.Request, key string) *image.RGBA {
c := appengine.NewContext(r)
dsObj, err := dsu.BufGet(w, r, "dsu.WrapBlob__"+key)
util_err.Err_http(w, r, err, false)
s := string(dsObj.VByte)
img, whichFormat := conv.Base64_str_to_img(s)
c.Infof("retrieved img from base64: format %v - subtype %T\n", whichFormat, img)
i, ok := img.(*image.RGBA)
util_err.Err_http(w, r, ok, false, "saved image needs to be reconstructible into a format png of subtype *image.RGBA")
return i
}
// An example demonstrating decoding JPEG img + examining its pixels.
func imageAnalyze(w http.ResponseWriter, r *http.Request, m map[string]interface{}) {
c := appengine.NewContext(r)
// Decode the JPEG data.
// If reading from file, create a reader with
// reader, err := os.Open("testdata/video-001.q50.420.jpeg")
// if err != nil { c.Errorf(err) }
// defer reader.Close()
img, whichFormat := conv.Base64_str_to_img(conv.Img_jpeg_base64)
c.Infof("retrieved img from base64: format %v - type %T\n", whichFormat, img)
bounds := img.Bounds()
// Calculate a 16-bin histogram for m's red, green, blue and alpha components.
// An image's bounds do not necessarily start at (0, 0), so the two loops start
// at bounds.Min.Y and bounds.Min.X. Looping over Y first and X second is more
// likely to result in better memory access patterns than X first and Y second.
var histogram [16][4]int
for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
for x := bounds.Min.X; x < bounds.Max.X; x++ {
r, g, b, a := img.At(x, y).RGBA()
// A color's RGBA method returns values in the range [0, 65535].
// Shifting by 12 reduces this to the range [0, 15].
histogram[r>>12][0]++
histogram[g>>12][1]++
histogram[b>>12][2]++
histogram[a>>12][3]++
}
}
b1 := new(bytes.Buffer)
s1 := fmt.Sprintf("%-14s %6s %6s %6s %6s\n", "bin", "red", "green", "blue", "alpha")
b1.WriteString(s1)
for i, x := range histogram {
s1 := fmt.Sprintf("0x%04x-0x%04x: %6d %6d %6d %6d\n", i<<12, (i+1)<<12-1, x[0], x[1], x[2], x[3])
b1.WriteString(s1)
}
w.Header().Set("Content-Type", "text/plain")
w.Write(b1.Bytes())
}