| // Copyright 2011 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| // Package bmp implements a BMP image decoder. |
| // |
| // The BMP specification is at http://www.digicamsoft.com/bmp/bmp.html. |
| package bmp |
| |
| import ( |
| "image/color" |
| "image" |
| "io" |
| "os" |
| ) |
| |
| // ErrUnsupported means that the input BMP image uses a valid but unsupported |
| // feature. |
| var ErrUnsupported = os.NewError("bmp: unsupported BMP image") |
| |
| func readUint16(b []byte) uint16 { |
| return uint16(b[0]) | uint16(b[1])<<8 |
| } |
| |
| func readUint32(b []byte) uint32 { |
| return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24 |
| } |
| |
| // decodePaletted reads an 8 bit-per-pixel BMP image from r. |
| func decodePaletted(r io.Reader, c image.Config) (image.Image, os.Error) { |
| var tmp [4]byte |
| paletted := image.NewPaletted(image.Rect(0, 0, c.Width, c.Height), c.ColorModel.(color.Palette)) |
| // BMP images are stored bottom-up rather than top-down. |
| for y := c.Height - 1; y >= 0; y-- { |
| p := paletted.Pix[y*paletted.Stride : y*paletted.Stride+c.Width] |
| _, err := io.ReadFull(r, p) |
| if err != nil { |
| return nil, err |
| } |
| // Each row is 4-byte aligned. |
| if c.Width%4 != 0 { |
| _, err := io.ReadFull(r, tmp[:4-c.Width%4]) |
| if err != nil { |
| return nil, err |
| } |
| } |
| } |
| return paletted, nil |
| } |
| |
| // decodeRGBA reads a 24 bit-per-pixel BMP image from r. |
| func decodeRGBA(r io.Reader, c image.Config) (image.Image, os.Error) { |
| rgba := image.NewRGBA(image.Rect(0, 0, c.Width, c.Height)) |
| // There are 3 bytes per pixel, and each row is 4-byte aligned. |
| b := make([]byte, (3*c.Width+3)&^3) |
| // BMP images are stored bottom-up rather than top-down. |
| for y := c.Height - 1; y >= 0; y-- { |
| _, err := io.ReadFull(r, b) |
| if err != nil { |
| return nil, err |
| } |
| p := rgba.Pix[y*rgba.Stride : y*rgba.Stride+c.Width*4] |
| for i, j := 0, 0; i < len(p); i, j = i+4, j+3 { |
| // BMP images are stored in BGR order rather than RGB order. |
| p[i+0] = b[j+2] |
| p[i+1] = b[j+1] |
| p[i+2] = b[j+0] |
| p[i+3] = 0xFF |
| } |
| } |
| return rgba, nil |
| } |
| |
| // Decode reads a BMP image from r and returns it as an image.Image. |
| // Limitation: The file must be 8 or 24 bits per pixel. |
| func Decode(r io.Reader) (image.Image, os.Error) { |
| c, err := DecodeConfig(r) |
| if err != nil { |
| return nil, err |
| } |
| if c.ColorModel == color.RGBAModel { |
| return decodeRGBA(r, c) |
| } |
| return decodePaletted(r, c) |
| } |
| |
| // DecodeConfig returns the color model and dimensions of a BMP image without |
| // decoding the entire image. |
| // Limitation: The file must be 8 or 24 bits per pixel. |
| func DecodeConfig(r io.Reader) (config image.Config, err os.Error) { |
| // We only support those BMP images that are a BITMAPFILEHEADER |
| // immediately followed by a BITMAPINFOHEADER. |
| const ( |
| fileHeaderLen = 14 |
| infoHeaderLen = 40 |
| ) |
| var b [1024]byte |
| if _, err = io.ReadFull(r, b[:fileHeaderLen+infoHeaderLen]); err != nil { |
| return |
| } |
| if string(b[:2]) != "BM" { |
| err = os.NewError("bmp: invalid format") |
| return |
| } |
| offset := readUint32(b[10:14]) |
| if readUint32(b[14:18]) != infoHeaderLen { |
| err = ErrUnsupported |
| return |
| } |
| width := int(readUint32(b[18:22])) |
| height := int(readUint32(b[22:26])) |
| if width < 0 || height < 0 { |
| err = ErrUnsupported |
| return |
| } |
| // We only support 1 plane, 8 or 24 bits per pixel and no compression. |
| planes, bpp, compression := readUint16(b[26:28]), readUint16(b[28:30]), readUint32(b[30:34]) |
| if planes != 1 || compression != 0 { |
| err = ErrUnsupported |
| return |
| } |
| switch bpp { |
| case 8: |
| if offset != fileHeaderLen+infoHeaderLen+256*4 { |
| err = ErrUnsupported |
| return |
| } |
| _, err = io.ReadFull(r, b[:256*4]) |
| if err != nil { |
| return |
| } |
| pcm := make(color.Palette, 256) |
| for i := range pcm { |
| // BMP images are stored in BGR order rather than RGB order. |
| // Every 4th byte is padding. |
| pcm[i] = color.RGBA{b[4*i+2], b[4*i+1], b[4*i+0], 0xFF} |
| } |
| return image.Config{pcm, width, height}, nil |
| case 24: |
| if offset != fileHeaderLen+infoHeaderLen { |
| err = ErrUnsupported |
| return |
| } |
| return image.Config{color.RGBAModel, width, height}, nil |
| } |
| err = ErrUnsupported |
| return |
| } |
| |
| func init() { |
| image.RegisterFormat("bmp", "BM????\x00\x00\x00\x00", Decode, DecodeConfig) |
| } |