Colin Cross | 7bb052a | 2015-02-03 12:59:37 -0800 | [diff] [blame^] | 1 | // Copyright 2009 The Go Authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | package png |
| 6 | |
| 7 | import ( |
| 8 | "bufio" |
| 9 | "compress/zlib" |
| 10 | "hash/crc32" |
| 11 | "image" |
| 12 | "image/color" |
| 13 | "io" |
| 14 | "strconv" |
| 15 | ) |
| 16 | |
| 17 | // Encoder configures encoding PNG images. |
| 18 | type Encoder struct { |
| 19 | CompressionLevel CompressionLevel |
| 20 | } |
| 21 | |
| 22 | type encoder struct { |
| 23 | enc *Encoder |
| 24 | w io.Writer |
| 25 | m image.Image |
| 26 | cb int |
| 27 | err error |
| 28 | header [8]byte |
| 29 | footer [4]byte |
| 30 | tmp [4 * 256]byte |
| 31 | } |
| 32 | |
| 33 | type CompressionLevel int |
| 34 | |
| 35 | const ( |
| 36 | DefaultCompression CompressionLevel = 0 |
| 37 | NoCompression CompressionLevel = -1 |
| 38 | BestSpeed CompressionLevel = -2 |
| 39 | BestCompression CompressionLevel = -3 |
| 40 | |
| 41 | // Positive CompressionLevel values are reserved to mean a numeric zlib |
| 42 | // compression level, although that is not implemented yet. |
| 43 | ) |
| 44 | |
| 45 | // Big-endian. |
| 46 | func writeUint32(b []uint8, u uint32) { |
| 47 | b[0] = uint8(u >> 24) |
| 48 | b[1] = uint8(u >> 16) |
| 49 | b[2] = uint8(u >> 8) |
| 50 | b[3] = uint8(u >> 0) |
| 51 | } |
| 52 | |
| 53 | type opaquer interface { |
| 54 | Opaque() bool |
| 55 | } |
| 56 | |
| 57 | // Returns whether or not the image is fully opaque. |
| 58 | func opaque(m image.Image) bool { |
| 59 | if o, ok := m.(opaquer); ok { |
| 60 | return o.Opaque() |
| 61 | } |
| 62 | b := m.Bounds() |
| 63 | for y := b.Min.Y; y < b.Max.Y; y++ { |
| 64 | for x := b.Min.X; x < b.Max.X; x++ { |
| 65 | _, _, _, a := m.At(x, y).RGBA() |
| 66 | if a != 0xffff { |
| 67 | return false |
| 68 | } |
| 69 | } |
| 70 | } |
| 71 | return true |
| 72 | } |
| 73 | |
| 74 | // The absolute value of a byte interpreted as a signed int8. |
| 75 | func abs8(d uint8) int { |
| 76 | if d < 128 { |
| 77 | return int(d) |
| 78 | } |
| 79 | return 256 - int(d) |
| 80 | } |
| 81 | |
| 82 | func (e *encoder) writeChunk(b []byte, name string) { |
| 83 | if e.err != nil { |
| 84 | return |
| 85 | } |
| 86 | n := uint32(len(b)) |
| 87 | if int(n) != len(b) { |
| 88 | e.err = UnsupportedError(name + " chunk is too large: " + strconv.Itoa(len(b))) |
| 89 | return |
| 90 | } |
| 91 | writeUint32(e.header[:4], n) |
| 92 | e.header[4] = name[0] |
| 93 | e.header[5] = name[1] |
| 94 | e.header[6] = name[2] |
| 95 | e.header[7] = name[3] |
| 96 | crc := crc32.NewIEEE() |
| 97 | crc.Write(e.header[4:8]) |
| 98 | crc.Write(b) |
| 99 | writeUint32(e.footer[:4], crc.Sum32()) |
| 100 | |
| 101 | _, e.err = e.w.Write(e.header[:8]) |
| 102 | if e.err != nil { |
| 103 | return |
| 104 | } |
| 105 | _, e.err = e.w.Write(b) |
| 106 | if e.err != nil { |
| 107 | return |
| 108 | } |
| 109 | _, e.err = e.w.Write(e.footer[:4]) |
| 110 | } |
| 111 | |
| 112 | func (e *encoder) writeIHDR() { |
| 113 | b := e.m.Bounds() |
| 114 | writeUint32(e.tmp[0:4], uint32(b.Dx())) |
| 115 | writeUint32(e.tmp[4:8], uint32(b.Dy())) |
| 116 | // Set bit depth and color type. |
| 117 | switch e.cb { |
| 118 | case cbG8: |
| 119 | e.tmp[8] = 8 |
| 120 | e.tmp[9] = ctGrayscale |
| 121 | case cbTC8: |
| 122 | e.tmp[8] = 8 |
| 123 | e.tmp[9] = ctTrueColor |
| 124 | case cbP8: |
| 125 | e.tmp[8] = 8 |
| 126 | e.tmp[9] = ctPaletted |
| 127 | case cbTCA8: |
| 128 | e.tmp[8] = 8 |
| 129 | e.tmp[9] = ctTrueColorAlpha |
| 130 | case cbG16: |
| 131 | e.tmp[8] = 16 |
| 132 | e.tmp[9] = ctGrayscale |
| 133 | case cbTC16: |
| 134 | e.tmp[8] = 16 |
| 135 | e.tmp[9] = ctTrueColor |
| 136 | case cbTCA16: |
| 137 | e.tmp[8] = 16 |
| 138 | e.tmp[9] = ctTrueColorAlpha |
| 139 | } |
| 140 | e.tmp[10] = 0 // default compression method |
| 141 | e.tmp[11] = 0 // default filter method |
| 142 | e.tmp[12] = 0 // non-interlaced |
| 143 | e.writeChunk(e.tmp[:13], "IHDR") |
| 144 | } |
| 145 | |
| 146 | func (e *encoder) writePLTEAndTRNS(p color.Palette) { |
| 147 | if len(p) < 1 || len(p) > 256 { |
| 148 | e.err = FormatError("bad palette length: " + strconv.Itoa(len(p))) |
| 149 | return |
| 150 | } |
| 151 | last := -1 |
| 152 | for i, c := range p { |
| 153 | c1 := color.NRGBAModel.Convert(c).(color.NRGBA) |
| 154 | e.tmp[3*i+0] = c1.R |
| 155 | e.tmp[3*i+1] = c1.G |
| 156 | e.tmp[3*i+2] = c1.B |
| 157 | if c1.A != 0xff { |
| 158 | last = i |
| 159 | } |
| 160 | e.tmp[3*256+i] = c1.A |
| 161 | } |
| 162 | e.writeChunk(e.tmp[:3*len(p)], "PLTE") |
| 163 | if last != -1 { |
| 164 | e.writeChunk(e.tmp[3*256:3*256+1+last], "tRNS") |
| 165 | } |
| 166 | } |
| 167 | |
| 168 | // An encoder is an io.Writer that satisfies writes by writing PNG IDAT chunks, |
| 169 | // including an 8-byte header and 4-byte CRC checksum per Write call. Such calls |
| 170 | // should be relatively infrequent, since writeIDATs uses a bufio.Writer. |
| 171 | // |
| 172 | // This method should only be called from writeIDATs (via writeImage). |
| 173 | // No other code should treat an encoder as an io.Writer. |
| 174 | func (e *encoder) Write(b []byte) (int, error) { |
| 175 | e.writeChunk(b, "IDAT") |
| 176 | if e.err != nil { |
| 177 | return 0, e.err |
| 178 | } |
| 179 | return len(b), nil |
| 180 | } |
| 181 | |
| 182 | // Chooses the filter to use for encoding the current row, and applies it. |
| 183 | // The return value is the index of the filter and also of the row in cr that has had it applied. |
| 184 | func filter(cr *[nFilter][]byte, pr []byte, bpp int) int { |
| 185 | // We try all five filter types, and pick the one that minimizes the sum of absolute differences. |
| 186 | // This is the same heuristic that libpng uses, although the filters are attempted in order of |
| 187 | // estimated most likely to be minimal (ftUp, ftPaeth, ftNone, ftSub, ftAverage), rather than |
| 188 | // in their enumeration order (ftNone, ftSub, ftUp, ftAverage, ftPaeth). |
| 189 | cdat0 := cr[0][1:] |
| 190 | cdat1 := cr[1][1:] |
| 191 | cdat2 := cr[2][1:] |
| 192 | cdat3 := cr[3][1:] |
| 193 | cdat4 := cr[4][1:] |
| 194 | pdat := pr[1:] |
| 195 | n := len(cdat0) |
| 196 | |
| 197 | // The up filter. |
| 198 | sum := 0 |
| 199 | for i := 0; i < n; i++ { |
| 200 | cdat2[i] = cdat0[i] - pdat[i] |
| 201 | sum += abs8(cdat2[i]) |
| 202 | } |
| 203 | best := sum |
| 204 | filter := ftUp |
| 205 | |
| 206 | // The Paeth filter. |
| 207 | sum = 0 |
| 208 | for i := 0; i < bpp; i++ { |
| 209 | cdat4[i] = cdat0[i] - pdat[i] |
| 210 | sum += abs8(cdat4[i]) |
| 211 | } |
| 212 | for i := bpp; i < n; i++ { |
| 213 | cdat4[i] = cdat0[i] - paeth(cdat0[i-bpp], pdat[i], pdat[i-bpp]) |
| 214 | sum += abs8(cdat4[i]) |
| 215 | if sum >= best { |
| 216 | break |
| 217 | } |
| 218 | } |
| 219 | if sum < best { |
| 220 | best = sum |
| 221 | filter = ftPaeth |
| 222 | } |
| 223 | |
| 224 | // The none filter. |
| 225 | sum = 0 |
| 226 | for i := 0; i < n; i++ { |
| 227 | sum += abs8(cdat0[i]) |
| 228 | if sum >= best { |
| 229 | break |
| 230 | } |
| 231 | } |
| 232 | if sum < best { |
| 233 | best = sum |
| 234 | filter = ftNone |
| 235 | } |
| 236 | |
| 237 | // The sub filter. |
| 238 | sum = 0 |
| 239 | for i := 0; i < bpp; i++ { |
| 240 | cdat1[i] = cdat0[i] |
| 241 | sum += abs8(cdat1[i]) |
| 242 | } |
| 243 | for i := bpp; i < n; i++ { |
| 244 | cdat1[i] = cdat0[i] - cdat0[i-bpp] |
| 245 | sum += abs8(cdat1[i]) |
| 246 | if sum >= best { |
| 247 | break |
| 248 | } |
| 249 | } |
| 250 | if sum < best { |
| 251 | best = sum |
| 252 | filter = ftSub |
| 253 | } |
| 254 | |
| 255 | // The average filter. |
| 256 | sum = 0 |
| 257 | for i := 0; i < bpp; i++ { |
| 258 | cdat3[i] = cdat0[i] - pdat[i]/2 |
| 259 | sum += abs8(cdat3[i]) |
| 260 | } |
| 261 | for i := bpp; i < n; i++ { |
| 262 | cdat3[i] = cdat0[i] - uint8((int(cdat0[i-bpp])+int(pdat[i]))/2) |
| 263 | sum += abs8(cdat3[i]) |
| 264 | if sum >= best { |
| 265 | break |
| 266 | } |
| 267 | } |
| 268 | if sum < best { |
| 269 | best = sum |
| 270 | filter = ftAverage |
| 271 | } |
| 272 | |
| 273 | return filter |
| 274 | } |
| 275 | |
| 276 | func writeImage(w io.Writer, m image.Image, cb int, level int) error { |
| 277 | zw, err := zlib.NewWriterLevel(w, level) |
| 278 | if err != nil { |
| 279 | return err |
| 280 | } |
| 281 | defer zw.Close() |
| 282 | |
| 283 | bpp := 0 // Bytes per pixel. |
| 284 | |
| 285 | switch cb { |
| 286 | case cbG8: |
| 287 | bpp = 1 |
| 288 | case cbTC8: |
| 289 | bpp = 3 |
| 290 | case cbP8: |
| 291 | bpp = 1 |
| 292 | case cbTCA8: |
| 293 | bpp = 4 |
| 294 | case cbTC16: |
| 295 | bpp = 6 |
| 296 | case cbTCA16: |
| 297 | bpp = 8 |
| 298 | case cbG16: |
| 299 | bpp = 2 |
| 300 | } |
| 301 | // cr[*] and pr are the bytes for the current and previous row. |
| 302 | // cr[0] is unfiltered (or equivalently, filtered with the ftNone filter). |
| 303 | // cr[ft], for non-zero filter types ft, are buffers for transforming cr[0] under the |
| 304 | // other PNG filter types. These buffers are allocated once and re-used for each row. |
| 305 | // The +1 is for the per-row filter type, which is at cr[*][0]. |
| 306 | b := m.Bounds() |
| 307 | var cr [nFilter][]uint8 |
| 308 | for i := range cr { |
| 309 | cr[i] = make([]uint8, 1+bpp*b.Dx()) |
| 310 | cr[i][0] = uint8(i) |
| 311 | } |
| 312 | pr := make([]uint8, 1+bpp*b.Dx()) |
| 313 | |
| 314 | gray, _ := m.(*image.Gray) |
| 315 | rgba, _ := m.(*image.RGBA) |
| 316 | paletted, _ := m.(*image.Paletted) |
| 317 | nrgba, _ := m.(*image.NRGBA) |
| 318 | |
| 319 | for y := b.Min.Y; y < b.Max.Y; y++ { |
| 320 | // Convert from colors to bytes. |
| 321 | i := 1 |
| 322 | switch cb { |
| 323 | case cbG8: |
| 324 | if gray != nil { |
| 325 | offset := (y - b.Min.Y) * gray.Stride |
| 326 | copy(cr[0][1:], gray.Pix[offset:offset+b.Dx()]) |
| 327 | } else { |
| 328 | for x := b.Min.X; x < b.Max.X; x++ { |
| 329 | c := color.GrayModel.Convert(m.At(x, y)).(color.Gray) |
| 330 | cr[0][i] = c.Y |
| 331 | i++ |
| 332 | } |
| 333 | } |
| 334 | case cbTC8: |
| 335 | // We have previously verified that the alpha value is fully opaque. |
| 336 | cr0 := cr[0] |
| 337 | stride, pix := 0, []byte(nil) |
| 338 | if rgba != nil { |
| 339 | stride, pix = rgba.Stride, rgba.Pix |
| 340 | } else if nrgba != nil { |
| 341 | stride, pix = nrgba.Stride, nrgba.Pix |
| 342 | } |
| 343 | if stride != 0 { |
| 344 | j0 := (y - b.Min.Y) * stride |
| 345 | j1 := j0 + b.Dx()*4 |
| 346 | for j := j0; j < j1; j += 4 { |
| 347 | cr0[i+0] = pix[j+0] |
| 348 | cr0[i+1] = pix[j+1] |
| 349 | cr0[i+2] = pix[j+2] |
| 350 | i += 3 |
| 351 | } |
| 352 | } else { |
| 353 | for x := b.Min.X; x < b.Max.X; x++ { |
| 354 | r, g, b, _ := m.At(x, y).RGBA() |
| 355 | cr0[i+0] = uint8(r >> 8) |
| 356 | cr0[i+1] = uint8(g >> 8) |
| 357 | cr0[i+2] = uint8(b >> 8) |
| 358 | i += 3 |
| 359 | } |
| 360 | } |
| 361 | case cbP8: |
| 362 | if paletted != nil { |
| 363 | offset := (y - b.Min.Y) * paletted.Stride |
| 364 | copy(cr[0][1:], paletted.Pix[offset:offset+b.Dx()]) |
| 365 | } else { |
| 366 | pi := m.(image.PalettedImage) |
| 367 | for x := b.Min.X; x < b.Max.X; x++ { |
| 368 | cr[0][i] = pi.ColorIndexAt(x, y) |
| 369 | i += 1 |
| 370 | } |
| 371 | } |
| 372 | case cbTCA8: |
| 373 | if nrgba != nil { |
| 374 | offset := (y - b.Min.Y) * nrgba.Stride |
| 375 | copy(cr[0][1:], nrgba.Pix[offset:offset+b.Dx()*4]) |
| 376 | } else { |
| 377 | // Convert from image.Image (which is alpha-premultiplied) to PNG's non-alpha-premultiplied. |
| 378 | for x := b.Min.X; x < b.Max.X; x++ { |
| 379 | c := color.NRGBAModel.Convert(m.At(x, y)).(color.NRGBA) |
| 380 | cr[0][i+0] = c.R |
| 381 | cr[0][i+1] = c.G |
| 382 | cr[0][i+2] = c.B |
| 383 | cr[0][i+3] = c.A |
| 384 | i += 4 |
| 385 | } |
| 386 | } |
| 387 | case cbG16: |
| 388 | for x := b.Min.X; x < b.Max.X; x++ { |
| 389 | c := color.Gray16Model.Convert(m.At(x, y)).(color.Gray16) |
| 390 | cr[0][i+0] = uint8(c.Y >> 8) |
| 391 | cr[0][i+1] = uint8(c.Y) |
| 392 | i += 2 |
| 393 | } |
| 394 | case cbTC16: |
| 395 | // We have previously verified that the alpha value is fully opaque. |
| 396 | for x := b.Min.X; x < b.Max.X; x++ { |
| 397 | r, g, b, _ := m.At(x, y).RGBA() |
| 398 | cr[0][i+0] = uint8(r >> 8) |
| 399 | cr[0][i+1] = uint8(r) |
| 400 | cr[0][i+2] = uint8(g >> 8) |
| 401 | cr[0][i+3] = uint8(g) |
| 402 | cr[0][i+4] = uint8(b >> 8) |
| 403 | cr[0][i+5] = uint8(b) |
| 404 | i += 6 |
| 405 | } |
| 406 | case cbTCA16: |
| 407 | // Convert from image.Image (which is alpha-premultiplied) to PNG's non-alpha-premultiplied. |
| 408 | for x := b.Min.X; x < b.Max.X; x++ { |
| 409 | c := color.NRGBA64Model.Convert(m.At(x, y)).(color.NRGBA64) |
| 410 | cr[0][i+0] = uint8(c.R >> 8) |
| 411 | cr[0][i+1] = uint8(c.R) |
| 412 | cr[0][i+2] = uint8(c.G >> 8) |
| 413 | cr[0][i+3] = uint8(c.G) |
| 414 | cr[0][i+4] = uint8(c.B >> 8) |
| 415 | cr[0][i+5] = uint8(c.B) |
| 416 | cr[0][i+6] = uint8(c.A >> 8) |
| 417 | cr[0][i+7] = uint8(c.A) |
| 418 | i += 8 |
| 419 | } |
| 420 | } |
| 421 | |
| 422 | // Apply the filter. |
| 423 | f := ftNone |
| 424 | if level != zlib.NoCompression { |
| 425 | f = filter(&cr, pr, bpp) |
| 426 | } |
| 427 | |
| 428 | // Write the compressed bytes. |
| 429 | if _, err := zw.Write(cr[f]); err != nil { |
| 430 | return err |
| 431 | } |
| 432 | |
| 433 | // The current row for y is the previous row for y+1. |
| 434 | pr, cr[0] = cr[0], pr |
| 435 | } |
| 436 | return nil |
| 437 | } |
| 438 | |
| 439 | // Write the actual image data to one or more IDAT chunks. |
| 440 | func (e *encoder) writeIDATs() { |
| 441 | if e.err != nil { |
| 442 | return |
| 443 | } |
| 444 | var bw *bufio.Writer |
| 445 | bw = bufio.NewWriterSize(e, 1<<15) |
| 446 | e.err = writeImage(bw, e.m, e.cb, levelToZlib(e.enc.CompressionLevel)) |
| 447 | if e.err != nil { |
| 448 | return |
| 449 | } |
| 450 | e.err = bw.Flush() |
| 451 | } |
| 452 | |
| 453 | // This function is required because we want the zero value of |
| 454 | // Encoder.CompressionLevel to map to zlib.DefaultCompression. |
| 455 | func levelToZlib(l CompressionLevel) int { |
| 456 | switch l { |
| 457 | case DefaultCompression: |
| 458 | return zlib.DefaultCompression |
| 459 | case NoCompression: |
| 460 | return zlib.NoCompression |
| 461 | case BestSpeed: |
| 462 | return zlib.BestSpeed |
| 463 | case BestCompression: |
| 464 | return zlib.BestCompression |
| 465 | default: |
| 466 | return zlib.DefaultCompression |
| 467 | } |
| 468 | } |
| 469 | |
| 470 | func (e *encoder) writeIEND() { e.writeChunk(nil, "IEND") } |
| 471 | |
| 472 | // Encode writes the Image m to w in PNG format. Any Image may be |
| 473 | // encoded, but images that are not image.NRGBA might be encoded lossily. |
| 474 | func Encode(w io.Writer, m image.Image) error { |
| 475 | var e Encoder |
| 476 | return e.Encode(w, m) |
| 477 | } |
| 478 | |
| 479 | // Encode writes the Image m to w in PNG format. |
| 480 | func (enc *Encoder) Encode(w io.Writer, m image.Image) error { |
| 481 | // Obviously, negative widths and heights are invalid. Furthermore, the PNG |
| 482 | // spec section 11.2.2 says that zero is invalid. Excessively large images are |
| 483 | // also rejected. |
| 484 | mw, mh := int64(m.Bounds().Dx()), int64(m.Bounds().Dy()) |
| 485 | if mw <= 0 || mh <= 0 || mw >= 1<<32 || mh >= 1<<32 { |
| 486 | return FormatError("invalid image size: " + strconv.FormatInt(mw, 10) + "x" + strconv.FormatInt(mh, 10)) |
| 487 | } |
| 488 | |
| 489 | var e encoder |
| 490 | e.enc = enc |
| 491 | e.w = w |
| 492 | e.m = m |
| 493 | |
| 494 | var pal color.Palette |
| 495 | // cbP8 encoding needs PalettedImage's ColorIndexAt method. |
| 496 | if _, ok := m.(image.PalettedImage); ok { |
| 497 | pal, _ = m.ColorModel().(color.Palette) |
| 498 | } |
| 499 | if pal != nil { |
| 500 | e.cb = cbP8 |
| 501 | } else { |
| 502 | switch m.ColorModel() { |
| 503 | case color.GrayModel: |
| 504 | e.cb = cbG8 |
| 505 | case color.Gray16Model: |
| 506 | e.cb = cbG16 |
| 507 | case color.RGBAModel, color.NRGBAModel, color.AlphaModel: |
| 508 | if opaque(m) { |
| 509 | e.cb = cbTC8 |
| 510 | } else { |
| 511 | e.cb = cbTCA8 |
| 512 | } |
| 513 | default: |
| 514 | if opaque(m) { |
| 515 | e.cb = cbTC16 |
| 516 | } else { |
| 517 | e.cb = cbTCA16 |
| 518 | } |
| 519 | } |
| 520 | } |
| 521 | |
| 522 | _, e.err = io.WriteString(w, pngHeader) |
| 523 | e.writeIHDR() |
| 524 | if pal != nil { |
| 525 | e.writePLTEAndTRNS(pal) |
| 526 | } |
| 527 | e.writeIDATs() |
| 528 | e.writeIEND() |
| 529 | return e.err |
| 530 | } |