feat: support bmp & tiff format

bmp.go

@@ -0,0 +1,137 @@
+// 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 and encoder.
+//
+// The BMP specification is at http://www.digicamsoft.com/bmp/bmp.html.
+package imgsz // import "golang.org/x/image/bmp"
+
+import (
+	"errors"
+	"image/color"
+	"io"
+)
+
+// ErrUnsupported means that the input BMP image uses a valid but unsupported
+// feature.
+var ErrUnsupported = errors.New("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
+}
+
+func decodebmp(r io.Reader) (size Size, err error) {
+	// We only support those BMP images with one of the following DIB headers:
+	// - BITMAPINFOHEADER (40 bytes)
+	// - BITMAPV4HEADER (108 bytes)
+	// - BITMAPV5HEADER (124 bytes)
+	const (
+		fileHeaderLen   = 14
+		infoHeaderLen   = 40
+		v4InfoHeaderLen = 108
+		v5InfoHeaderLen = 124
+	)
+	var b [1024]byte
+	if _, err := io.ReadFull(r, b[:fileHeaderLen+4]); err != nil {
+		if err == io.EOF {
+			err = io.ErrUnexpectedEOF
+		}
+		return Size{}, err
+	}
+	if string(b[:2]) != "BM" {
+		return Size{}, errors.New("bmp: invalid format")
+	}
+	offset := readUint32(b[10:14])
+	infoLen := readUint32(b[14:18])
+	if infoLen != infoHeaderLen && infoLen != v4InfoHeaderLen && infoLen != v5InfoHeaderLen {
+		return Size{}, ErrUnsupported
+	}
+	if _, err := io.ReadFull(r, b[fileHeaderLen+4:fileHeaderLen+infoLen]); err != nil {
+		if err == io.EOF {
+			err = io.ErrUnexpectedEOF
+		}
+		return Size{}, err
+	}
+	width := int(int32(readUint32(b[18:22])))
+	height := int(int32(readUint32(b[22:26])))
+	if height < 0 {
+		height = -height
+	}
+	if width < 0 || height < 0 {
+		return Size{}, ErrUnsupported
+	}
+	// We only support 1 plane and 8, 24 or 32 bits per pixel and no
+	// compression.
+	planes, bpp, compression := readUint16(b[26:28]), readUint16(b[28:30]), readUint32(b[30:34])
+	// if compression is set to BI_BITFIELDS, but the bitmask is set to the default bitmask
+	// that would be used if compression was set to 0, we can continue as if compression was 0
+	if compression == 3 && infoLen > infoHeaderLen &&
+		readUint32(b[54:58]) == 0xff0000 && readUint32(b[58:62]) == 0xff00 &&
+		readUint32(b[62:66]) == 0xff && readUint32(b[66:70]) == 0xff000000 {
+		compression = 0
+	}
+	if planes != 1 || compression != 0 {
+		return Size{}, ErrUnsupported
+	}
+	switch bpp {
+	case 8:
+		colorUsed := readUint32(b[46:50])
+		// If colorUsed is 0, it is set to the maximum number of colors for the given bpp, which is 2^bpp.
+		if colorUsed == 0 {
+			colorUsed = 256
+		} else if colorUsed > 256 {
+			return Size{}, ErrUnsupported
+		}
+
+		if offset != fileHeaderLen+infoLen+colorUsed*4 {
+			return Size{}, ErrUnsupported
+		}
+		_, err = io.ReadFull(r, b[:colorUsed*4])
+		if err != nil {
+			return Size{}, err
+		}
+		pcm := make(color.Palette, colorUsed)
+		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 Size{Width: width, Height: height}, nil
+	case 24:
+		if offset != fileHeaderLen+infoLen {
+			return Size{}, ErrUnsupported
+		}
+		return Size{Width: width, Height: height}, nil
+	case 32:
+		if offset != fileHeaderLen+infoLen {
+			return Size{}, ErrUnsupported
+		}
+		// 32 bits per pixel is possibly RGBX (X is padding) or RGBA (A is
+		// alpha transparency). However, for BMP images, "Alpha is a
+		// poorly-documented and inconsistently-used feature" says
+		// https://source.chromium.org/chromium/chromium/src/+/bc0a792d7ebc587190d1a62ccddba10abeea274b:third_party/blink/renderer/platform/image-decoders/bmp/bmp_image_reader.cc;l=621
+		//
+		// That goes on to say "BITMAPV3HEADER+ have an alpha bitmask in the
+		// info header... so we respect it at all times... [For earlier
+		// (smaller) headers we] ignore alpha in Windows V3 BMPs except inside
+		// ICO files".
+		//
+		// "Ignore" means to always set alpha to 0xFF (fully opaque):
+		// https://source.chromium.org/chromium/chromium/src/+/bc0a792d7ebc587190d1a62ccddba10abeea274b:third_party/blink/renderer/platform/image-decoders/bmp/bmp_image_reader.h;l=272
+		//
+		// Confusingly, "Windows V3" does not correspond to BITMAPV3HEADER, but
+		// instead corresponds to the earlier (smaller) BITMAPINFOHEADER:
+		// https://source.chromium.org/chromium/chromium/src/+/bc0a792d7ebc587190d1a62ccddba10abeea274b:third_party/blink/renderer/platform/image-decoders/bmp/bmp_image_reader.cc;l=258
+		//
+		// This Go package does not support ICO files and the (infoLen >
+		// infoHeaderLen) condition distinguishes BITMAPINFOHEADER (40 bytes)
+		// vs later (larger) headers.
+		return Size{Width: width, Height: height}, nil
+	}
+	return Size{}, ErrUnsupported
+}