func Decode(r io.Reader) (img image.Image, er error) {
/* Reading the whole file in may be inefficient, but libjpeg wants callbacks
* to functions to read in more data, and that is a nightmare to implement. We
* don't want to read the entire stream, however, which means pulling the header.
* We may be able to read enough to call jpeg_read_header with a [10]byte, but
* I'll change it later if need be, since this probably doesn't play nicely
* with a non-closing io.Reader */
var wholeFile []byte
if wholeFile, er = ioutil.ReadAll(r); er != nil {
return
}
var cinfo C.struct_jpeg_decompress_struct
var jerr C.struct_jpeg_error_mgr
cinfo.err = C.jpeg_std_error(&jerr)
C.jpeg_CreateDecompress(&cinfo, C.JPEG_LIB_VERSION, C.size_t(unsafe.Sizeof(cinfo)))
C.jpeg_mem_src(&cinfo, (*C.uchar)(unsafe.Pointer(&wholeFile[0])), C.ulong(len(wholeFile)))
if C.jpeg_read_header(&cinfo, C.TRUE) == C.JPEG_HEADER_OK {
C.jpeg_start_decompress(&cinfo)
if cinfo.num_components == 1 {
img = decodeGrayscale(&cinfo)
} else if cinfo.num_components == 3 {
img = decodeRGB(&cinfo)
} else if cinfo.num_components == 4 {
img = decodeCMYK(&cinfo)
} else {
er = fmt.Errorf("Invalid number of components (%d)", cinfo.num_components)
}
if er == nil {
C.jpeg_finish_decompress(&cinfo)
}
}
C.jpeg_destroy_decompress(&cinfo)
return
}
// ReadJPEG reads a JPEG file and returns a planar YUV image.
func ReadJPEG(src io.Reader, params DecompressionParameters) (img *YUVImage, err error) {
defer func() {
if r := recover(); r != nil {
img = nil
var ok bool
err, ok = r.(error)
if !ok {
err = fmt.Errorf("JPEG error: %v", r)
}
}
}()
dinfo := (*C.struct_jpeg_decompress_struct)(C.malloc(C.size_t(unsafe.Sizeof(C.struct_jpeg_decompress_struct{}))))
if dinfo == nil {
panic("Failed to allocate dinfo")
}
defer C.free(unsafe.Pointer(dinfo))
dinfo.err = (*C.struct_jpeg_error_mgr)(C.malloc(C.size_t(unsafe.Sizeof(C.struct_jpeg_error_mgr{}))))
if dinfo.err == nil {
panic("Failed to allocate dinfo.err")
}
defer C.free(unsafe.Pointer(dinfo.err))
img = new(YUVImage)
// Setup error handling
C.jpeg_std_error(dinfo.err)
dinfo.err.error_exit = (*[0]byte)(C.error_panic)
// Initialize decompression
C.c_jpeg_create_decompress(dinfo)
defer C.jpeg_destroy_decompress(dinfo)
srcManager := makeSourceManager(src, dinfo)
defer C.free(unsafe.Pointer(srcManager))
C.jpeg_read_header(dinfo, C.TRUE)
// Configure pre-scaling and request calculation of component info
if params.TargetWidth > 0 && params.TargetHeight > 0 {
var scaleFactor int
for scaleFactor = 1; scaleFactor <= 8; scaleFactor++ {
if ((scaleFactor*int(dinfo.image_width)+7)/8) >= params.TargetWidth &&
((scaleFactor*int(dinfo.image_height)+7)/8) >= params.TargetHeight {
break
}
}
if scaleFactor < 8 {
dinfo.scale_num = C.uint(scaleFactor)
dinfo.scale_denom = 8
}
}
// More settings
if params.FastDCT {
dinfo.dct_method = C.JDCT_IFAST
} else {
dinfo.dct_method = C.JDCT_ISLOW
}
C.jpeg_calc_output_dimensions(dinfo)
// Figure out what color format we're dealing with after scaling
compInfo := (*[3]C.jpeg_component_info)(unsafe.Pointer(dinfo.comp_info))
colorVDiv := 1
switch dinfo.num_components {
case 1:
if dinfo.jpeg_color_space != C.JCS_GRAYSCALE {
panic("Unsupported colorspace")
}
img.Format = Grayscale
case 3:
// No support for RGB and CMYK (both rare)
if dinfo.jpeg_color_space != C.JCS_YCbCr {
panic("Unsupported colorspace")
}
dwY := compInfo[Y].downsampled_width
dhY := compInfo[Y].downsampled_height
dwC := compInfo[U].downsampled_width
dhC := compInfo[U].downsampled_height
//fmt.Printf("%d %d %d %d\n", dwY, dhY, dwC, dhC)
if dwC != compInfo[V].downsampled_width || dhC != compInfo[V].downsampled_height {
panic("Unsupported color subsampling (Cb and Cr differ)")
}
// Since the decisions about which DCT size and subsampling mode
// to use, if any, are complex, instead just check the calculated
// output plane sizes and infer the subsampling mode from that.
if dwY == dwC {
if dhY == dhC {
img.Format = YUV444
} else if (dhY+1)/2 == dhC {
img.Format = YUV440
colorVDiv = 2
} else {
panic("Unsupported color subsampling (vertical is not 1 or 2)")
}
} else if (dwY+1)/2 == dwC {
if dhY == dhC {
img.Format = YUV422
} else if (dhY+1)/2 == dhC {
img.Format = YUV420
colorVDiv = 2
} else {
panic("Unsupported color subsampling (vertical is not 1 or 2)")
}
} else {
panic("Unsupported color subsampling (horizontal is not 1 or 2)")
}
default:
panic("Unsupported number of components")
}
img.Width = int(compInfo[Y].downsampled_width)
img.Height = int(compInfo[Y].downsampled_height)
//fmt.Printf("%dx%d (format: %d)\n", img.Width, img.Height, img.Format)
//fmt.Printf("Output: %dx%d\n", dinfo.output_width, dinfo.output_height)
// libjpeg raw data out is in planar format, which avoids unnecessary
// planar->packed->planar conversions.
dinfo.raw_data_out = C.TRUE
// Allocate image planes
for i := 0; i < int(dinfo.num_components); i++ {
/*fmt.Printf("%d: %dx%d (DCT %dx%d, %dx%d blocks sf %dx%d)\n", i,
compInfo[i].downsampled_width, compInfo[i].downsampled_height,
compInfo[i].DCT_scaled_size, compInfo[i].DCT_scaled_size,
compInfo[i].width_in_blocks, compInfo[i].height_in_blocks,
compInfo[i].h_samp_factor, compInfo[i].v_samp_factor)*/
// When downsampling, odd modes like 14x14 may be used. Pad to AlignSize
// (16) and then add an extra AlignSize padding, to cover overflow from
// any such modes.
img.Stride[i] = pad(int(compInfo[i].downsampled_width), AlignSize) + AlignSize
height := pad(int(compInfo[i].downsampled_height), AlignSize) + AlignSize
img.Data[i] = make([]byte, img.Stride[i]*height)
}
// Start decompression
C.jpeg_start_decompress(dinfo)
// Allocate JSAMPIMAGE to hold pointers to one iMCU worth of image data
// this is a safe overestimate; we use the return value from
// jpeg_read_raw_data to figure out what is the actual iMCU row count.
var yuvPtrInt [3][AlignSize]C.JSAMPROW
yuvPtr := [3]C.JSAMPARRAY{
C.JSAMPARRAY(unsafe.Pointer(&yuvPtrInt[0][0])),
C.JSAMPARRAY(unsafe.Pointer(&yuvPtrInt[1][0])),
C.JSAMPARRAY(unsafe.Pointer(&yuvPtrInt[2][0])),
}
// Decode the image.
var row C.JDIMENSION
var iMCURows int
for i := 0; i < int(dinfo.num_components); i++ {
compRows := int(C.DCT_v_scaled_size(dinfo, C.int(i)) * compInfo[i].v_samp_factor)
if compRows > iMCURows {
iMCURows = compRows
}
}
//fmt.Printf("iMCU_rows: %d (div: %d)\n", iMCURows, colorVDiv)
for row = 0; row < dinfo.output_height; {
// First fill in the pointers into the plane data buffers
for i := 0; i < int(dinfo.num_components); i++ {
for j := 0; j < iMCURows; j++ {
compRow := (int(row) + j)
if i > 0 {
compRow = (int(row)/colorVDiv + j)
}
yuvPtrInt[i][j] = C.JSAMPROW(unsafe.Pointer(&img.Data[i][img.Stride[i]*compRow]))
}
}
// Get the data
row += C.jpeg_read_raw_data(dinfo, C.JSAMPIMAGE(unsafe.Pointer(&yuvPtr[0])), C.JDIMENSION(2*iMCURows))
}
// Clean up
C.jpeg_finish_decompress(dinfo)
return
}