Add support for depth of PNG

lib/image_loader.lua

@@ -11,7 +11,8 @@ function image_loader.decode_float(blob)
    end
    return im, alpha, blob
 end
-function image_loader.encode_png(rgb, alpha)
+function image_loader.encode_png(rgb, alpha, depth)
+   depth = depth or 8
    if rgb:type() == "torch.ByteTensor" then
       rgb = rgb:float():div(255)
    end
@@ -26,15 +27,16 @@ function image_loader.encode_png(rgb, alpha)
       rgba[4]:copy(alpha)
       local im = gm.Image():fromTensor(rgba, "RGBA", "DHW")
       im:format("png")
-      return im:toBlob(9)
+      return im:depth(depth):toBlob(9)
    else
       local im = gm.Image(rgb, "RGB", "DHW")
       im:format("png")
-      return im:toBlob(9)
+      return im:depth(depth):toBlob(9)
    end
 end
-function image_loader.save_png(filename, rgb, alpha)
-   local blob, len = image_loader.encode_png(rgb, alpha)
+function image_loader.save_png(filename, rgb, alpha, depth)
+   depth = depth or 8
+   local blob, len = image_loader.encode_png(rgb, alpha, depth)
    local fp = io.open(filename, "wb")
    if not fp then
       error("IO error: " .. filename)