Commit Graph

280 Commits

Author SHA1 Message Date
Nigel Tao
eecb4e626f shiny/font: new package for drawing text on an image.
Package font defines an interface for font faces.

Other packages provide font face implementations. For example, a
truetype package (not part of this CL) would provide one based on .ttf
font files.

This CL also introduces the golang.org/x/exp/shiny/font/plan9font
package, a concrete implementation of the font.Face interface for the
Plan 9 bitmap font format.

Change-Id: Iead8914caaa58c7562b18a86b45002ae47486903
Reviewed-on: https://go-review.googlesource.com/13463
Reviewed-by: Rob Pike <r@golang.org>
2015-08-11 05:46:15 +00:00
Nigel Tao
3029cff51e math/fixed: add point types.
Change-Id: Ie9ae62eab3c484034ee8207a2b2e573ec6f1464e
Reviewed-on: https://go-review.googlesource.com/13294
Reviewed-by: Rob Pike <r@golang.org>
2015-08-07 00:23:53 +00:00
Nigel Tao
8e3389fa81 draw: have Scale and Transform recognize straight copies.
This is only for the NearestNeighbor and ApproxBiLinear Interpolators. A
Kernel interpolator will add blur even when the dst and src rectangles
are the same size.

We do not bother recognizing Transforms that are Scales. The performance
difference is minimal, as you still need to do a per-dst-pixel inverse
mapping either way.

benchmark                           old ns/op     new ns/op     delta
BenchmarkSimpleScaleCopy-8          4866297       29586         -99.39%
BenchmarkSimpleTransformCopy-8      4875991       29531         -99.39%
BenchmarkSimpleTransformScale-8     1208147       1223206       +1.25%

Change-Id: If649ad27a4e81bcbb24b18315745c02c9186a5b7
Reviewed-on: https://go-review.googlesource.com/13004
Reviewed-by: Rob Pike <r@golang.org>
2015-08-02 10:47:07 +00:00
Nigel Tao
5ec5e003b2 math/fixed: new package.
Fixes golang/go#11906

Change-Id: I2b43311ff145e8453cd255f085c82add6da7de5b
Reviewed-on: https://go-review.googlesource.com/12863
Reviewed-by: Rob Pike <r@golang.org>
2015-07-30 06:07:28 +00:00
Nigel Tao
5f5d3e0618 draw: skip TestFastPaths for Go 1.4.
Fixes golang/go#11921

Change-Id: Iafca8b21523d486ce9b2be494b8fb93216573968
Reviewed-on: https://go-review.googlesource.com/12861
Reviewed-by: Andrew Gerrand <adg@golang.org>
2015-07-30 05:48:34 +00:00
Russ Cox
c6de6b60d2 vp8: split expression to placate 386 compiler
Fixes golang/go#11917.

Change-Id: I2eff23bd98be7531d9a115714ca50e45d3064584
Reviewed-on: https://go-review.googlesource.com/12856
Reviewed-by: Ian Lance Taylor <iant@golang.org>
2015-07-29 22:52:57 +00:00
Nigel Tao
5c9906b535 image/draw: have Transform take a f64.Aff3 instead of a *f64.Aff3.
It's more args (in terms of bytes), but fewer allocations (Transformer
is an interface). Either way, it's not really that big of a deal, but
the value instead of the pointer seems conceptually more correct.

Change-Id: Ibea76da17cbda0d9633110fd56044b4e2c690e81
Reviewed-on: https://go-review.googlesource.com/12669
Reviewed-by: Rob Pike <r@golang.org>
2015-07-29 01:18:37 +00:00
Nigel Tao
8ca9b58be9 shiny/screen: new package.
Change-Id: Ib0a6296b9c117d64fc76fc6abe59ccb7da3bbae1
Reviewed-on: https://go-review.googlesource.com/12568
Reviewed-by: Rob Pike <r@golang.org>
2015-07-24 06:42:10 +00:00
Nigel Tao
6b7a488d1e draw: tweak the YCbCr to RGBA conversion formula.
This is the golang.org/x equivalent of the golang.org/cl/12220 change to
the standard library.

Change-Id: I220d1398902dec374472ef5b08db8501607cc971
Reviewed-on: https://go-review.googlesource.com/12222
Reviewed-by: Rob Pike <r@golang.org>
2015-07-15 05:30:06 +00:00
Nigel Tao
92cae9f9bc tiff/lzw: sync (yet again) to the upstream lzw in the stdlib.
This picks up a recent change:
https://go-review.googlesource.com/#/c/11661/

Change-Id: I0309f7b804e0d88ea623c8ae97b65cd0c2bad101
Reviewed-on: https://go-review.googlesource.com/11850
Reviewed-by: David Symonds <dsymonds@golang.org>
2015-07-02 03:36:51 +00:00
Nigel Tao
eb11b45157 tiff/lzw: sync (again) to the upstream lzw in the stdlib.
I somehow missed this in the previous change. Not sure how.

Change-Id: Ib9277944418a73cda6acc07fc308d846b4064b9e
Reviewed-on: https://go-review.googlesource.com/11321
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2015-06-22 01:01:28 +00:00
Nigel Tao
ef56035c4b tiff/lzw: sync to the upstream lzw in the stdlib.
Change-Id: If6086ada81498327c61e91b18d135aa255401e68
Reviewed-on: https://go-review.googlesource.com/11320
Reviewed-by: David Symonds <dsymonds@golang.org>
2015-06-22 00:56:16 +00:00
Jeff R. Allen
090ed236cf image/tiff: replace repeated error creations with one
Make all occurrences of "not enough pixel data" refer to the
same one.

Change-Id: Iecff9f22eba7a8852174ba18d1e68226c76f84c6
Reviewed-on: https://go-review.googlesource.com/11030
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2015-06-22 00:40:40 +00:00
Nigel Tao
d6cb0a28ce tiff: re-organize some test cases, and make comment style consistent.
There is no code changes in this CL, just a copy/paste and some
wordsmithing.

Change-Id: I418e8aed5ab997fad4214e8049287cac4bce8bf6
Reviewed-on: https://go-review.googlesource.com/11274
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2015-06-19 07:18:22 +00:00
Nigel Tao
e5f3f2f6c0 tiff: format the find/replace test strings consistently.
Change-Id: Id3222a76702e8f2017aec77a25df715ef378c8ef
Reviewed-on: https://go-review.googlesource.com/11224
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2015-06-18 23:38:30 +00:00
Jeff R. Allen
b7cdfbb5c4 image/tiff: fix a panic with invalid tile sizes
Fuzzing detected that an invalid tile size could cause a
panic. Fix a typo in the range check to solve it.

Fixes golang/go#10712.

Change-Id: I88a5a7884d98f622cc89ed6e394becebb07c6e60
Reviewed-on: https://go-review.googlesource.com/11020
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2015-06-18 01:57:12 +00:00
Nigel Tao
9af7e1b58b tiff: don't apply the 8 bps predictor to a 1 bps image.
Change-Id: I112fc7189f8afdd54b96562e1989f9fca1d24d68
Reviewed-on: https://go-review.googlesource.com/11135
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2015-06-18 01:44:20 +00:00
Jeff R. Allen
3157439762 image/tiff: do not allow zero bits per sample
Fuzzing detected a divide by zero in images with 0 bits
per sample. Instead of panicing, return an error. Do more
validation of bits per sample so that the package only
supports what we've actually tested.

Fixes golang/go#10711.

Change-Id: Ib41b5cd798c32b06429164c9bc471f5f321d88c5
Reviewed-on: https://go-review.googlesource.com/10943
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2015-06-16 21:37:07 +00:00
Nigel Tao
d8e202c6ce vp8: limit all other partitions to 1<<24 bytes in size, not just N-1 of
them.

Also check for int32 overflow in the webp package.

Fixes #10790.

Change-Id: Id1162fad8a467a72a5379c7f4432d64ef25bc37a
Reviewed-on: https://go-review.googlesource.com/10072
Reviewed-by: Rob Pike <r@golang.org>
2015-05-15 01:02:58 +00:00
Aamir Khan
c5f9292598 vp8l: don't ignore I/O errors when reading LZ77 parameters.
Fixes golang/go#10383

Change-Id: I3e5e357a40a45189c31f0b4db9422dedc351c910
Reviewed-on: https://go-review.googlesource.com/9912
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2015-05-11 04:53:56 +00:00
Aamir Khan
25eff15cb8 webp: fix panic in case of invalid chunkID
At the time of decoding webp file, if chunkID is not one of
{'ALPH', 'VP8', 'VP8L', 'VP8X'} return errInvalidFormat

Fixes golang/go#10384

Change-Id: I167909b5ddef174d161f806297a08fac6aabcf19
Reviewed-on: https://go-review.googlesource.com/9839
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2015-05-11 04:53:49 +00:00
Nigel Tao
f28211f6e1 bmp: optimize decoding and encoding 0xH sized images.
It should be quick regardless of how large H is.

Fixes golang/go#10746

Change-Id: Icde36047e88d9786e64f44724b7ba8b38db2a33f
Reviewed-on: https://go-review.googlesource.com/9836
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2015-05-11 00:10:33 +00:00
chai2010
4a3ed0c124 tiff: don't panic on reading bad ifd
Fixes golang/go#10597

Change-Id: I57b3614de7181134cf4bd0ca9dc9ff879d3d2e3d
Reviewed-on: https://go-review.googlesource.com/9414
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2015-05-05 06:22:24 +00:00
Nigel Tao
70cb8023e6 draw: make op a mandatory argument, not optional.
Change-Id: Ic08ce587cf458444b098b752f0fa7ab16d43c914
Reviewed-on: https://go-review.googlesource.com/9468
Reviewed-by: Rob Pike <r@golang.org>
2015-05-04 06:41:52 +00:00
Benny Siegert
6af46c2009 tiff: reject IFDs whose data is longer than int.
Fixes golang/go#10596

Change-Id: Ib5035569e84c67868c7f278281620f6c9b11b470
Reviewed-on: https://go-review.googlesource.com/9378
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2015-05-04 03:48:26 +00:00
Nigel Tao
918b3735c3 draw: disable the image.Rectangle DstMask fast path until Go 1.5 is
released.

Change-Id: Ie5d6766d53952d3a81dfbd19a9f4022aaad6af5a
Reviewed-on: https://go-review.googlesource.com/9463
Reviewed-by: Rob Pike <r@golang.org>
2015-04-29 03:28:00 +00:00
Nigel Tao
b2f48f3f51 tiff: don't panic on reading short block data.
Fixes golang/go#10394

Change-Id: I12621650f0c21579047497407ca2745febe4521b
Reviewed-on: https://go-review.googlesource.com/9278
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2015-04-28 01:06:15 +00:00
Håvard Haugen
72a6583050 x/image/tiff: fix division by zero when decoding empty image
Return a zero width or zero height image of the appropriate type.

Fixes golang/go#10393.

Change-Id: I3aa7b6125447726600fb072ce1e8682373ce2a57
Reviewed-on: https://go-review.googlesource.com/9182
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2015-04-28 00:39:31 +00:00
Nigel Tao
95ece4346f cmd/webp-manual-test: add a "build ignore" tag, so that "go install
golang.org/x/image/..." doesn't install the manual testing program.

Also add a missing copyright notice.

Change-Id: I7ab0a438df09ac8882e7d2482d2bf96d4260f8eb
Reviewed-on: https://go-review.googlesource.com/9277
Reviewed-by: Rob Pike <r@golang.org>
2015-04-27 00:40:42 +00:00
Nigel Tao
8642173156 draw: implement srcMask.
Change-Id: Ibf710521f466847afaf2d005dc8a2bb817169298
Reviewed-on: https://go-review.googlesource.com/9276
Reviewed-by: Rob Pike <r@golang.org>
2015-04-26 09:25:24 +00:00
chai2010
f681781743 tiff: fix shadowed err variable.
Fixes golang/go#10395

Change-Id: Ice768df7bb0bdac979d49328bfdf0d6713a1e7c3
Reviewed-on: https://go-review.googlesource.com/9264
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2015-04-24 01:40:59 +00:00
Nigel Tao
24b0de15f1 draw: add a fast path for an image.Rectangle DstMask.
Change-Id: Id5227b9d217b56a342bc1ffc735dababa8a9e3e9
Reviewed-on: https://go-review.googlesource.com/9233
Reviewed-by: Rob Pike <r@golang.org>
2015-04-24 00:51:48 +00:00
Nigel Tao
b621bdc118 draw: delete some dead code.
Change-Id: I5830755b0be52df2be536a918f47684a1b7eda9d
Reviewed-on: https://go-review.googlesource.com/9232
Reviewed-by: Rob Pike <r@golang.org>
2015-04-22 05:24:54 +00:00
Nigel Tao
3940ddb240 draw: implement dstMask.
Change-Id: Id63695c3cef67fbe79fa1fbe916b85108f401093
Reviewed-on: https://go-review.googlesource.com/9191
Reviewed-by: Rob Pike <r@golang.org>
2015-04-22 04:18:19 +00:00
Nigel Tao
76b4869e5a draw: factor out some float64 to uint32 conversions.
This will make the upcoming "implement masks" change easier.

Change-Id: I2b316a0b25f98779d9cd076e64266c617464a08e
Reviewed-on: https://go-review.googlesource.com/8999
Reviewed-by: Rob Pike <r@golang.org>
2015-04-21 01:05:21 +00:00
Nigel Tao
26bd17363f draw: plumb the Options through to the type-specific code.
It'll only be used by the fallback code paths, but it's easiest if all
code paths take the extra argument.

Change-Id: I09c4067df6af7c4cd270e8ffcad96d1d8af29057
Reviewed-on: https://go-review.googlesource.com/8909
Reviewed-by: Rob Pike <r@golang.org>
2015-04-16 23:50:31 +00:00
Nigel Tao
69a0d8f9aa draw: add mask fields to Options.
This change only adds the fields, more or less. Follow-up changes will
actually honor the masks.

Change-Id: I81411dc1aac4b3c846dcdf13e2cb0b5cd60fb2b4
Reviewed-on: https://go-review.googlesource.com/8902
Reviewed-by: Rob Pike <r@golang.org>
2015-04-16 00:20:49 +00:00
Nigel Tao
e83a2376af draw: refactor codegen to use argf instead of fmt.Sprintf.
Change-Id: Iee4cb1b605c381b75a688a5e65e9afc4d34df193
Reviewed-on: https://go-review.googlesource.com/8900
Reviewed-by: Rob Pike <r@golang.org>
2015-04-14 01:31:41 +00:00
Nigel Tao
8ed4ff0a33 draw: implement the Over operator.
Change-Id: Id207b8f2fa5233175285800477e60f111ef4af63
Reviewed-on: https://go-review.googlesource.com/8744
Reviewed-by: Rob Pike <r@golang.org>
2015-04-13 23:42:02 +00:00
Nigel Tao
697863cec6 draw: clamp kernel output so red, green and blue <= alpha.
The raw computation can produce red > alpha when some weights are
negative.

Change-Id: Ic6701354770f012d3ef21a390a8400e14e9d1e25
Reviewed-on: https://go-review.googlesource.com/8740
Reviewed-by: Rob Pike <r@golang.org>
2015-04-10 05:40:26 +00:00
Nigel Tao
67c770d218 draw: substitute Src for Over when the source image is completely opaque.
The two Ops are equivalent, but Src is faster.

Change-Id: I2c73a13755047c224c71fb5af786875f02681de9
Reviewed-on: https://go-review.googlesource.com/8640
Reviewed-by: Rob Pike <r@golang.org>
2015-04-08 22:38:33 +00:00
Nigel Tao
65a798f031 draw: generate code for op == Over.
This change just does the mechanical codegen for the op == Over cases.
The actual compositing operator is still effectively Src. Fixing that,
which is less mechanical, will be a follow-up change.

Change-Id: I87805114d49e7ce7087066187a2f4c722a883c01
Reviewed-on: https://go-review.googlesource.com/8524
Reviewed-by: Rob Pike <r@golang.org>
2015-04-07 22:35:06 +00:00
Nigel Tao
b293696c81 draw: switch on the Op compositing operator.
This change only *prepares* the codegen to handle multiple Ops. The
actual generated code still only supports one Op (Src) and not the other
(Over). A follow-up change will add Over.

This Op switch (an eventual x2 multiplier in the amount of code
generated) should be the last of the codegen LoC multipliers. The dst
and src mask options will be implemented in the slow path fallback.

Change-Id: Iecbcc6fad063e2aac36d78d5380c0a0947c709df
Reviewed-on: https://go-review.googlesource.com/8488
Reviewed-by: Rob Pike <r@golang.org>
2015-04-07 06:16:14 +00:00
Nigel Tao
c53fa16781 draw: use a sync.Pool for kernel scaling's temporary buffers.
benchmark                      old ns/op     new ns/op     delta
BenchmarkScaleBLLargeDown      257715146     260286012     +1.00%
BenchmarkScaleCRLargeDown      426797448     430078734     +0.77%
BenchmarkScaleBLDown           4449939       4222542       -5.11%
BenchmarkScaleCRDown           8160446       8010056       -1.84%
BenchmarkScaleBLUp             22290312      21044122      -5.59%
BenchmarkScaleCRUp             33010722      32021468      -3.00%
BenchmarkScaleCRSrcGray        13307961      13020192      -2.16%
BenchmarkScaleCRSrcNRGBA       40567431      40801939      +0.58%
BenchmarkScaleCRSrcRGBA        39892971      40240558      +0.87%
BenchmarkScaleCRSrcYCbCr       59020222      59686699      +1.13%

benchmark                      old allocs     new allocs     delta
BenchmarkScaleBLLargeDown      1              1              +0.00%
BenchmarkScaleCRLargeDown      1              2              +100.00%
BenchmarkScaleBLDown           1              0              -100.00%
BenchmarkScaleCRDown           1              0              -100.00%
BenchmarkScaleBLUp             1              0              -100.00%
BenchmarkScaleCRUp             1              0              -100.00%
BenchmarkScaleCRSrcGray        1              0              -100.00%
BenchmarkScaleCRSrcNRGBA       1              0              -100.00%
BenchmarkScaleCRSrcRGBA        1              0              -100.00%
BenchmarkScaleCRSrcYCbCr       1              0              -100.00%

benchmark                      old bytes     new bytes     delta
BenchmarkScaleBLLargeDown      14745600      2949200       -80.00%
BenchmarkScaleCRLargeDown      14745600      4915333       -66.67%
BenchmarkScaleBLDown           1523712       5079          -99.67%
BenchmarkScaleCRDown           1523712       7619          -99.50%
BenchmarkScaleBLUp             10117120      101175        -99.00%
BenchmarkScaleCRUp             10117120      202350        -98.00%
BenchmarkScaleCRSrcGray        4915200       49156         -99.00%
BenchmarkScaleCRSrcNRGBA       4915200       163853        -96.67%
BenchmarkScaleCRSrcRGBA        4915200       163853        -96.67%
BenchmarkScaleCRSrcYCbCr       4915200       245780        -95.00%

The increase in BenchmarkScale??LargeDown number of allocs I think is an
accounting error due to the low number of iterations: a low denominator.
I suspect that there are one or two extra allocs up front for using the
sync.Pool, but one fewer alloc per iteration. The number of iterations
is only 5 for BL and 3 for CR, for the default timeout. If I increase
the -test.benchtime value to 5s, then the reported average (allocs/op)
drop from 2 to 0, so the delta should actually be -100% instead of +0 or
+100%.

Change-Id: I21d9bb0086bdb25517b6a430e8a21bdf3db026f6
Reviewed-on: https://go-review.googlesource.com/8150
Reviewed-by: Rob Pike <r@golang.org>
2015-04-02 05:39:46 +00:00
Nigel Tao
d5c5125b57 draw: update the inlined YCbCr.RGBA code to use 16 bit color.
This matches the standard library change at
https://go-review.googlesource.com/#/c/8073/

Change-Id: I216028e18678a70e449167cd9ab910c63d37adcc
Reviewed-on: https://go-review.googlesource.com/8075
Reviewed-by: Rob Pike <r@golang.org>
2015-03-26 22:31:54 +00:00
Nigel Tao
500a27f912 draw: optimize some multiply-by-zeroes in Kernel.Transform.
benchmark                      old ns/op     new ns/op     delta
BenchmarkTformCRSrcGray        5096041       4820642       -5.40%
BenchmarkTformCRSrcNRGBA       10476578      8414331       -19.68%
BenchmarkTformCRSrcRGBA        10361135      7954413       -23.23%
BenchmarkTformCRSrcYCbCr       11952218      9824899       -17.80%

Change-Id: I8b4cfe68ecae85e447ae65ceecf185261445a8a2
Reviewed-on: https://go-review.googlesource.com/7991
Reviewed-by: Rob Pike <r@golang.org>
2015-03-25 21:02:11 +00:00
Nigel Tao
575b100276 draw: eliminate some math.Floor calls in Transform methods.
benchmark                      old ns/op     new ns/op     delta
BenchmarkTformNNSrcRGBA        524533        293230        -44.10%
BenchmarkTformNNSrcUniform     362974        149389        -58.84%
BenchmarkTformABSrcGray        827461        427720        -48.31%
BenchmarkTformABSrcNRGBA       1286930       919391        -28.56%
BenchmarkTformABSrcRGBA        1115444       794334        -28.79%
BenchmarkTformABSrcYCbCr       1732420       1379846       -20.35%
BenchmarkTformCRSrcGray        3629048       3467404       -4.45%
BenchmarkTformCRSrcNRGBA       7569407       7418874       -1.99%
BenchmarkTformCRSrcRGBA        7552459       7432745       -1.59%
BenchmarkTformCRSrcYCbCr       8072351       7854715       -2.70%

Change-Id: I6c01e631d9f88c36ae99d0cd181104ad5ac48db0
Reviewed-on: https://go-review.googlesource.com/7926
Reviewed-by: Rob Pike <r@golang.org>
2015-03-23 22:47:47 +00:00
Nigel Tao
41f747b91e draw: inline the generated YCbCrToRGB calls.
benchmark                      old ns/op     new ns/op     delta
BenchmarkScaleLargeDownNN      1302036       1168046       -10.29%
BenchmarkScaleLargeDownAB      3995006       3447621       -13.70%
BenchmarkScaleLargeDownBL      455470707     387598726     -14.90%
BenchmarkScaleLargeDownCR      818317661     679199442     -17.00%
BenchmarkScaleSrcYCbCr         3965076       3422325       -13.69%
BenchmarkTformABSrcYCbCr       2921253       2551934       -12.64%
BenchmarkTformCRSrcYCbCr       14839184      12263956      -17.35%

Change-Id: I60dcb5c00a30709fdc6616cbc8c2fc48ec3a8b14
Reviewed-on: https://go-review.googlesource.com/7921
Reviewed-by: Rob Pike <r@golang.org>
2015-03-23 00:17:39 +00:00
Nigel Tao
7eedc6044d draw: add Scale and Transform fast paths for Uniform src images.
benchmark                      old ns/op     new ns/op     delta
BenchmarkScaleSrcUniform       1744610       6305          -99.64%
BenchmarkTformABSrcUniform     586201        520028        -11.29%
BenchmarkTformCRSrcUniform     586952        519151        -11.55%

Change-Id: Ide9148f9e91bb6ec607fa7e9d78b35772ca189fe
Reviewed-on: https://go-review.googlesource.com/7881
Reviewed-by: Rob Pike <r@golang.org>
2015-03-21 04:28:23 +00:00
Nigel Tao
4180bcbc4a draw: inline the generated PixOffset calls.
Only the YCbCr benchmarks show significant changes. The other benchmark
changes look noisy. The PixOffset and YOffset calls were previously
already inlined by the gc compiler. COffset was different because it's
more complicated than YOffset, and the switch inside the COffset body is
redundant when you already know the src image sratio.
http://golang.org/src/image/ycbcr.go?s=2377:2414#L77

benchmark                      old ns/op     new ns/op     delta
BenchmarkScaleLargeDownNN      1037504       908236        -12.46%
BenchmarkScaleLargeDownAB      3196568       2735776       -14.42%
BenchmarkScaleLargeDownBL      357165552     311463393     -12.80%
BenchmarkScaleLargeDownCR      649403305     544985134     -16.08%
BenchmarkScaleSrcYCbCr         3204063       2699147       -15.76%
BenchmarkTformABSrcYCbCr       2155142       1968540       -8.66%
BenchmarkTformCRSrcYCbCr       11672625      9865358       -15.48%

Change-Id: Ifa109363a1282ab114b2fdb0b577dcafef927333
Reviewed-on: https://go-review.googlesource.com/7880
Reviewed-by: Rob Pike <r@golang.org>
2015-03-21 04:17:09 +00:00