code review 4374043: image/yuv: new package.

image/ycbcr: new package.

[nigeltao, 2011-04-07 00:57:29]

Hello r, rsc (cc: golang-dev@googlegroups.com, raph),

I'd like you to review this change to
https://go.googlecode.com/hg/

[nigeltao_gnome, 2011-04-07 01:01:25]

On 7 April 2011 10:57,  <nigeltao@golang.org> wrote:
> image/yuv: new package.

I'm thinking of changing jpeg.Decode to return a YUV image (i.e. its
natural representation) instead of an RGBA image, the same way that
png.Decode returns an NRGBA instead of an RGBA, but that will be a
separate changeset.

Also, exp/draw will probably need a fast path, but similarly, that's a
separate changeset.

[r, 2011-04-07 20:51:16]

let's decide on the name first. to me, this isn't YUV but YCbCr and i think the
package shouldn't be called yuv. ycbcr is probably right.  i think it's ok to
ignore that it's really y'cbcr because this model is the one everyone will
recognize, as long as the comments explain that.

http://codereview.appspot.com/4374043/diff/4001/src/pkg/image/yuv/yuv.go
File src/pkg/image/yuv/yuv.go (right):

http://codereview.appspot.com/4374043/diff/4001/src/pkg/image/yuv/yuv.go#newc...
src/pkg/image/yuv/yuv.go:9: // Strictly speaking, it implements the YCbCr color
model (as the term YUV
strictly speaking, i think this is Y'CbCr

http://codereview.appspot.com/4374043/diff/4001/src/pkg/image/yuv/yuv.go#newc...
src/pkg/image/yuv/yuv.go:15: // the JFIF specification at
http://www.w3.org/Graphics/JPEG/jfif3.pdf.
JPEG uses Y' not Y, i'm pretty sure.

http://codereview.appspot.com/4374043/diff/4001/src/pkg/image/yuv/yuv.go#newc...
src/pkg/image/yuv/yuv.go:26: //	Y  =  0.2990*R + 0.5870*G + 0.1140*B
this looks like Y'

http://codereview.appspot.com/4374043/diff/4001/src/pkg/image/yuv/yuv_test.go
File src/pkg/image/yuv/yuv_test.go (right):

http://codereview.appspot.com/4374043/diff/4001/src/pkg/image/yuv/yuv_test.go...
src/pkg/image/yuv/yuv_test.go:17: }
if x >= y {
  return x - y
}
return y - x

http://codereview.appspot.com/4374043/diff/4001/src/pkg/image/yuv/yuv_test.go...
src/pkg/image/yuv/yuv_test.go:27: if delta(r, int(r1)) > 1 || delta(g, int(g1))
> 1 || delta(b, int(b1)) > 1 {
if the rhs of delta is always a uint8, make that the signature of delta.

[nigeltao, 2011-04-10 01:27:39]

I've renamed it from yuv to ycbcr. PTAL.

[r, 2011-04-11 18:44:32]

LGTM
thanks

[nigeltao, 2011-04-12 12:32:19]

*** Submitted as http://code.google.com/p/go/source/detail?r=44dd4f4c2703 ***

image/ycbcr: new package.

R=r, rsc, nigeltao_gnome
CC=golang-dev, raph
http://codereview.appspot.com/4374043