go.image/bmp: support decoding 32-bit BMPs, as well as top-down BMPs.
Tested manually, from "dwebp -bmp" output. dwebp comes from https://developers.google.com/speed/webp/download LGTM=bsiegert R=bsiegert CC=golang-codereviews https://golang.org/cl/148020043
This commit is contained in:
Nigel Tao
parent
a704c116ac
commit
3bcf25db01
116
bmp/reader.go
116
bmp/reader.go
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@ -27,14 +27,17 @@ func readUint32(b []byte) uint32 {
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}
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// decodePaletted reads an 8 bit-per-pixel BMP image from r.
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func decodePaletted(r io.Reader, c image.Config) (image.Image, error) {
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// If topDown is false, the image rows will be read bottom-up.
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func decodePaletted(r io.Reader, c image.Config, topDown bool) (image.Image, error) {
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var tmp [4]byte
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paletted := image.NewPaletted(image.Rect(0, 0, c.Width, c.Height), c.ColorModel.(color.Palette))
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// BMP images are stored bottom-up rather than top-down.
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for y := c.Height - 1; y >= 0; y-- {
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y0, y1, yDelta := c.Height-1, -1, -1
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if topDown {
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y0, y1, yDelta = 0, c.Height, +1
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}
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for y := y0; y != y1; y += yDelta {
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p := paletted.Pix[y*paletted.Stride : y*paletted.Stride+c.Width]
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_, err := io.ReadFull(r, p)
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if err != nil {
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if _, err := io.ReadFull(r, p); err != nil {
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return nil, err
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}
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// Each row is 4-byte aligned.
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@ -48,15 +51,18 @@ func decodePaletted(r io.Reader, c image.Config) (image.Image, error) {
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return paletted, nil
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}
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// decodeRGBA reads a 24 bit-per-pixel BMP image from r.
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func decodeRGBA(r io.Reader, c image.Config) (image.Image, error) {
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// decodeRGB reads a 24 bit-per-pixel BMP image from r.
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// If topDown is false, the image rows will be read bottom-up.
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func decodeRGB(r io.Reader, c image.Config, topDown bool) (image.Image, error) {
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rgba := image.NewRGBA(image.Rect(0, 0, c.Width, c.Height))
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// There are 3 bytes per pixel, and each row is 4-byte aligned.
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b := make([]byte, (3*c.Width+3)&^3)
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// BMP images are stored bottom-up rather than top-down.
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for y := c.Height - 1; y >= 0; y-- {
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_, err := io.ReadFull(r, b)
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if err != nil {
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y0, y1, yDelta := c.Height-1, -1, -1
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if topDown {
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y0, y1, yDelta = 0, c.Height, +1
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}
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for y := y0; y != y1; y += yDelta {
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if _, err := io.ReadFull(r, b); err != nil {
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return nil, err
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}
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p := rgba.Pix[y*rgba.Stride : y*rgba.Stride+c.Width*4]
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@ -71,23 +77,54 @@ func decodeRGBA(r io.Reader, c image.Config) (image.Image, error) {
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return rgba, nil
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}
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// decodeNRGBA reads a 32 bit-per-pixel BMP image from r.
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// If topDown is false, the image rows will be read bottom-up.
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func decodeNRGBA(r io.Reader, c image.Config, topDown bool) (image.Image, error) {
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rgba := image.NewNRGBA(image.Rect(0, 0, c.Width, c.Height))
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y0, y1, yDelta := c.Height-1, -1, -1
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if topDown {
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y0, y1, yDelta = 0, c.Height, +1
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}
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for y := y0; y != y1; y += yDelta {
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p := rgba.Pix[y*rgba.Stride : y*rgba.Stride+c.Width*4]
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if _, err := io.ReadFull(r, p); err != nil {
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return nil, err
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}
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for i := 0; i < len(p); i += 4 {
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// BMP images are stored in BGRA order rather than RGBA order.
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p[i+0], p[i+2] = p[i+2], p[i+0]
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}
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}
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return rgba, nil
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}
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// Decode reads a BMP image from r and returns it as an image.Image.
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// Limitation: The file must be 8 or 24 bits per pixel.
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// Limitation: The file must be 8, 24 or 32 bits per pixel.
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func Decode(r io.Reader) (image.Image, error) {
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c, err := DecodeConfig(r)
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c, bpp, topDown, err := decodeConfig(r)
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if err != nil {
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return nil, err
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}
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if c.ColorModel == color.RGBAModel {
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return decodeRGBA(r, c)
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switch bpp {
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case 8:
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return decodePaletted(r, c, topDown)
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case 24:
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return decodeRGB(r, c, topDown)
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case 32:
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return decodeNRGBA(r, c, topDown)
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}
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return decodePaletted(r, c)
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panic("unreachable")
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}
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// DecodeConfig returns the color model and dimensions of a BMP image without
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// decoding the entire image.
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// Limitation: The file must be 8 or 24 bits per pixel.
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func DecodeConfig(r io.Reader) (config image.Config, err error) {
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// Limitation: The file must be 8, 24 or 32 bits per pixel.
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func DecodeConfig(r io.Reader) (image.Config, error) {
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config, _, _, err := decodeConfig(r)
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return config, err
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}
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func decodeConfig(r io.Reader) (config image.Config, bitsPerPixel int, topDown bool, err error) {
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// We only support those BMP images that are a BITMAPFILEHEADER
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// immediately followed by a BITMAPINFOHEADER.
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const (
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@ -95,39 +132,37 @@ func DecodeConfig(r io.Reader) (config image.Config, err error) {
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infoHeaderLen = 40
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)
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var b [1024]byte
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if _, err = io.ReadFull(r, b[:fileHeaderLen+infoHeaderLen]); err != nil {
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return
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if _, err := io.ReadFull(r, b[:fileHeaderLen+infoHeaderLen]); err != nil {
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return image.Config{}, 0, false, err
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}
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if string(b[:2]) != "BM" {
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err = errors.New("bmp: invalid format")
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return
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return image.Config{}, 0, false, errors.New("bmp: invalid format")
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}
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offset := readUint32(b[10:14])
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if readUint32(b[14:18]) != infoHeaderLen {
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err = ErrUnsupported
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return
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return image.Config{}, 0, false, ErrUnsupported
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}
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width := int(int32(readUint32(b[18:22])))
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height := int(int32(readUint32(b[22:26])))
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if height < 0 {
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height, topDown = -height, true
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}
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width := int(readUint32(b[18:22]))
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height := int(readUint32(b[22:26]))
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if width < 0 || height < 0 {
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err = ErrUnsupported
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return
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return image.Config{}, 0, false, ErrUnsupported
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}
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// We only support 1 plane, 8 or 24 bits per pixel and no compression.
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planes, bpp, compression := readUint16(b[26:28]), readUint16(b[28:30]), readUint32(b[30:34])
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if planes != 1 || compression != 0 {
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err = ErrUnsupported
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return
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return image.Config{}, 0, false, ErrUnsupported
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}
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switch bpp {
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case 8:
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if offset != fileHeaderLen+infoHeaderLen+256*4 {
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err = ErrUnsupported
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return
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return image.Config{}, 0, false, ErrUnsupported
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}
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_, err = io.ReadFull(r, b[:256*4])
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if err != nil {
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return
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return image.Config{}, 0, false, err
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}
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pcm := make(color.Palette, 256)
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for i := range pcm {
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@ -135,16 +170,19 @@ func DecodeConfig(r io.Reader) (config image.Config, err error) {
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// Every 4th byte is padding.
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pcm[i] = color.RGBA{b[4*i+2], b[4*i+1], b[4*i+0], 0xFF}
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}
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return image.Config{ColorModel: pcm, Width: width, Height: height}, nil
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return image.Config{ColorModel: pcm, Width: width, Height: height}, 8, topDown, nil
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case 24:
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if offset != fileHeaderLen+infoHeaderLen {
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err = ErrUnsupported
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return
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return image.Config{}, 0, false, ErrUnsupported
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}
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return image.Config{ColorModel: color.RGBAModel, Width: width, Height: height}, nil
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return image.Config{ColorModel: color.RGBAModel, Width: width, Height: height}, 24, topDown, nil
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case 32:
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if offset != fileHeaderLen+infoHeaderLen {
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return image.Config{}, 0, false, ErrUnsupported
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}
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return image.Config{ColorModel: color.RGBAModel, Width: width, Height: height}, 32, topDown, nil
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}
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err = ErrUnsupported
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return
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return image.Config{}, 0, false, ErrUnsupported
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}
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func init() {
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