func useLossless(image *vips.Image, options SaveOptions) bool {
if !options.Lossless {
return false
}
if !options.LossyIfPhoto {
return true
}
// Mobile devices start being unwilling to load >= 3 megapixel PNGs.
// Also we don't want to bother to edge detect on large images.
if image.Xsize()*image.Ysize() >= 3*1024*1024 {
return false
}
// Take a histogram of a Sobel edge detect of our image. What's the
// highest number of histogram values in a row that are more than 1%
// of the maximum value? Above 16 indicates a photo.
metric, err := image.PhotoMetric(0.01)
return err != nil || metric < 16
}
