initial commit

webp/yuva_image.go

@@ -0,0 +1,56 @@
+package webp
+
+import "image"
+
+// YUVAImage represents a image of YUV colors with alpha channel image.
+//
+// We can not insert WebP planer image into image.YCbCr,
+// because image.YCbCr is not compatible with ITU-R BT.601, but JFIF/JPEG one.
+//
+// See: http://en.wikipedia.org/wiki/YCbCr
+type YUVAImage struct {
+	Y, Cb, Cr, A []uint8
+	YStride      int
+	CStride      int
+	AStride      int
+	ColorSpace   ColorSpace
+	Rect         image.Rectangle
+}
+
+// NewYUVAImage creates and allocates image buffer.
+func NewYUVAImage(r image.Rectangle, c ColorSpace) (image *YUVAImage) {
+	yw, yh := r.Dx(), r.Dx()
+	cw, ch := ((r.Max.X+1)/2 - r.Min.X/2), ((r.Max.Y+1)/2 - r.Min.Y/2)
+
+	switch c {
+	case YUV420:
+		b := make([]byte, yw*yh+2*cw*ch)
+		image = &YUVAImage{
+			Y:          b[:yw*yh],
+			Cb:         b[yw*yh+0*cw*ch : yw*yh+1*cw*ch],
+			Cr:         b[yw*yh+1*cw*ch : yw*yh+2*cw*ch],
+			A:          nil,
+			YStride:    yw,
+			CStride:    cw,
+			AStride:    0,
+			ColorSpace: c,
+			Rect:       r,
+		}
+
+	case YUV420A:
+		b := make([]byte, 2*yw*yh+2*cw*ch)
+		image = &YUVAImage{
+			Y:          b[:yw*yh],
+			Cb:         b[yw*yh+0*cw*ch : yw*yh+1*cw*ch],
+			Cr:         b[yw*yh+1*cw*ch : yw*yh+2*cw*ch],
+			A:          b[yw*yh+2*cw*ch:],
+			YStride:    yw,
+			CStride:    cw,
+			AStride:    yw,
+			ColorSpace: c,
+			Rect:       r,
+		}
+	}
+
+	return
+}