On Thu, Sep 29, 2016 at 3:19 AM, Rodolfo Carvalho <rhcarva...@gmail.com> wrote:
> gift [3]: > y := 0.299*px.R + 0.587*px.G + 0.114*px.B > > I did not understand why image/color adds an extra 0.5 (500/1000) to y. > Could anybody give me a clue? > To directly answer your question: *GIFT also adds 0.5 to round off. * Wanna know where? Try to make up a call stack: gift.Grayscale() > returns Filter > is colorFilter > has a callback fn > returns pixel > contains float32s pixel is a struct containing float32s Filter is an interface, made of Draw() and Bounds() colorFilter implements Filter So, it eventually boils down to: [1] *colorFilter.Draw() > parallelize() > newPixelSetter().SetPixel() > f32u16() color.Color uses uint32s while gift.pixel uses float32s. I guess gift uses floats for cosmetic reasons. But they both round off while applying the grayscale filter. [1] https://github.com/disintegration/gift/blob/703be73d60d8baeaa84c47be0d31551b466ea84a/pixels.go#L304 -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
