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reader.go
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/
reader.go
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// Copyright 2023-2024 Florian Zwoch <fzwoch@gmail.com>. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package tj3 provides a simple JPEG decoder and encoder wrapper for the
// TurboJPEG v3 API and library.
package tj3
// #include <turbojpeg.h>
import "C"
import (
"errors"
"image"
"image/color"
"io"
)
// Decode reads a JPEG image from r and returns it as an [image.Image].
func Decode(r io.Reader) (image.Image, error) {
ctx := C.tj3Init(C.TJINIT_DECOMPRESS)
if ctx == nil {
return nil, errors.New("tj3Init() failed")
}
defer C.tj3Destroy(ctx)
b, err := io.ReadAll(r)
if err != nil {
return nil, err
}
ret := C.tj3DecompressHeader(ctx, (*C.uchar)(&b[0]), C.size_t(len(b)))
if ret != 0 {
return nil, errors.New(C.GoString(C.tj3GetErrorStr(ctx)))
}
if C.tj3Get(ctx, C.TJPARAM_PRECISION) != 8 {
return nil, errors.New("image is not 8-bit")
}
bounds := image.Rectangle{
Max: image.Point{
X: int(C.tj3Get(ctx, C.TJPARAM_JPEGWIDTH)),
Y: int(C.tj3Get(ctx, C.TJPARAM_JPEGHEIGHT)),
},
}
switch C.tj3Get(ctx, C.TJPARAM_COLORSPACE) {
case C.TJCS_GRAY:
img := image.NewGray(bounds)
ret = C.tj3Decompress8(ctx, (*C.uchar)(&b[0]), C.size_t(len(b)), (*C.uchar)(&img.Pix[0]), 0, C.TJPF_GRAY)
if ret != 0 {
return nil, errors.New(C.GoString(C.tj3GetErrorStr(ctx)))
}
return img, nil
case C.TJCS_YCCK:
img := image.NewCMYK(bounds)
ret = C.tj3Decompress8(ctx, (*C.uchar)(&b[0]), C.size_t(len(b)), (*C.uchar)(&img.Pix[0]), 0, C.TJPF_CMYK)
if ret != 0 {
return nil, errors.New(C.GoString(C.tj3GetErrorStr(ctx)))
}
return img, nil
case C.TJCS_RGB:
img := image.NewNRGBA(bounds)
ret = C.tj3Decompress8(ctx, (*C.uchar)(&b[0]), C.size_t(len(b)), (*C.uchar)(&img.Pix[0]), 0, C.TJPF_RGBA)
if ret != 0 {
return nil, errors.New(C.GoString(C.tj3GetErrorStr(ctx)))
}
return img, nil
case C.TJCS_YCbCr:
var ss image.YCbCrSubsampleRatio
switch C.tj3Get(ctx, C.TJPARAM_SUBSAMP) {
case C.TJSAMP_420:
ss = image.YCbCrSubsampleRatio420
case C.TJSAMP_422:
ss = image.YCbCrSubsampleRatio422
case C.TJSAMP_444:
ss = image.YCbCrSubsampleRatio444
}
img := image.NewYCbCr(bounds, ss)
ret = C.tj3DecompressToYUV8(ctx, (*C.uchar)(&b[0]), C.size_t(len(b)), (*C.uchar)(&img.Y[0]), 1)
if ret != 0 {
return nil, errors.New(C.GoString(C.tj3GetErrorStr(ctx)))
}
return img, nil
}
return nil, errors.New("")
}
// DecodeConfig returns the color model and dimensions of a JPEG image without
// decoding the entire image.
func DecodeConfig(r io.Reader) (image.Config, error) {
ctx := C.tj3Init(C.TJINIT_DECOMPRESS)
if ctx == nil {
return image.Config{}, errors.New("tj3Init() failed")
}
defer C.tj3Destroy(ctx)
b := make([]byte, 4096)
s, err := io.ReadFull(r, b)
if err != nil && err != io.ErrUnexpectedEOF {
return image.Config{}, err
}
ret := C.tj3DecompressHeader(ctx, (*C.uchar)(&b[0]), C.size_t(s))
if ret != 0 {
return image.Config{}, errors.New(C.GoString(C.tj3GetErrorStr(ctx)))
}
if C.tj3Get(ctx, C.TJPARAM_PRECISION) != 8 {
return image.Config{}, errors.New("image is not 8-bit")
}
w := int(C.tj3Get(ctx, C.TJPARAM_JPEGWIDTH))
h := int(C.tj3Get(ctx, C.TJPARAM_JPEGHEIGHT))
switch C.tj3Get(ctx, C.TJPARAM_COLORSPACE) {
case C.TJCS_GRAY:
return image.Config{
ColorModel: color.GrayModel,
Width: w,
Height: h,
}, nil
case C.TJCS_YCCK:
return image.Config{
ColorModel: color.CMYKModel,
Width: w,
Height: h,
}, nil
case C.TJCS_RGB:
return image.Config{
ColorModel: color.NRGBAModel,
Width: w,
Height: h,
}, nil
case C.TJCS_YCbCr:
return image.Config{
ColorModel: color.YCbCrModel,
Width: w,
Height: h,
}, nil
}
return image.Config{}, errors.New("")
}
func init() {
image.RegisterFormat("tj3", "\xff\xd8", Decode, DecodeConfig)
}