Thanks everyone for the answers and links. I computed a pixel-to-pixel difference and indeed what I was getting was -1/+1 differences in the gray values, due to rounding.
Next free time I'll try the other formulas. Thank you again, Rodolfo Carvalho On Thu, Sep 29, 2016 at 6:12 AM, Micky <mickylmar...@gmail.com> wrote: > > > 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.
