diff --git a/bmp.go b/bmp.go
new file mode 100644
index 0000000..4cc7d94
--- /dev/null
+++ b/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
+}
diff --git a/image_test.go b/image_test.go
index 7e4a3ad..b2080b0 100644
--- a/image_test.go
+++ b/image_test.go
@@ -57,4 +57,30 @@ func TestSizes(t *testing.T) {
 		t.Fatal(sz, n)
 	}
 	f.Close()
+
+	f, err = os.Open("testdata/test.bmp")
+	if err != nil {
+		t.Fatal(err)
+	}
+	sz, n, err = DecodeSize(f)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if sz.Width != 677 || sz.Height != 487 || n != "bmp" {
+		t.Fatal(sz, n)
+	}
+	f.Close()
+
+	f, err = os.Open("testdata/test.tiff")
+	if err != nil {
+		t.Fatal(err)
+	}
+	sz, n, err = DecodeSize(f)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if sz.Width != 1032 || sz.Height != 1457 || n != "tiff" {
+		t.Fatal(sz, n)
+	}
+	f.Close()
 }
diff --git a/init.go b/init.go
index 4bb2110..053e880 100644
--- a/init.go
+++ b/init.go
@@ -16,4 +16,7 @@ func init() {
 		return Size{d.width, d.height}, nil
 	})
 	RegisterFormat("webp", "RIFF????WEBPVP8", decodewebp)
+	RegisterFormat("bmp", "BM????\x00\x00\x00\x00", decodebmp)
+	RegisterFormat("tiff", leHeader, decodetiff)
+	RegisterFormat("tiff", beHeader, decodetiff)
 }
diff --git a/testdata/test.bmp b/testdata/test.bmp
new file mode 100644
index 0000000..fea1e45
Binary files /dev/null and b/testdata/test.bmp differ
diff --git a/testdata/test.tiff b/testdata/test.tiff
new file mode 100644
index 0000000..6a5a68b
Binary files /dev/null and b/testdata/test.tiff differ
diff --git a/tiff.go b/tiff.go
new file mode 100644
index 0000000..f4c14cc
--- /dev/null
+++ b/tiff.go
@@ -0,0 +1,255 @@
+// 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 tiff implements a TIFF image tiffdecoder and encoder.
+//
+// The TIFF specification is at http://partners.adobe.com/public/developer/en/tiff/TIFF6.pdf
+package imgsz // import "golang.org/x/image/tiff"
+
+import (
+	"encoding/binary"
+	"image/color"
+	"io"
+	"math"
+)
+
+const maxChunkSize = 10 << 20 // 10M
+
+// safeReadAt is a verbatim copy of internal/saferio.ReadDataAt from the
+// standard library, which is used to read data from a reader using a length
+// provided by untrusted data, without allocating the entire slice ahead of time
+// if it is large (>maxChunkSize). This allows us to avoid allocating giant
+// slices before learning that we can't actually read that much data from the
+// reader.
+func safeReadAt(r io.ReaderAt, n uint64, off int64) ([]byte, error) {
+	if int64(n) < 0 || n != uint64(int(n)) {
+		// n is too large to fit in int, so we can't allocate
+		// a buffer large enough. Treat this as a read failure.
+		return nil, io.ErrUnexpectedEOF
+	}
+
+	if n < maxChunkSize {
+		buf := make([]byte, n)
+		_, err := r.ReadAt(buf, off)
+		if err != nil {
+			// io.SectionReader can return EOF for n == 0,
+			// but for our purposes that is a success.
+			if err != io.EOF || n > 0 {
+				return nil, err
+			}
+		}
+		return buf, nil
+	}
+
+	var buf []byte
+	buf1 := make([]byte, maxChunkSize)
+	for n > 0 {
+		next := n
+		if next > maxChunkSize {
+			next = maxChunkSize
+		}
+		_, err := r.ReadAt(buf1[:next], off)
+		if err != nil {
+			return nil, err
+		}
+		buf = append(buf, buf1[:next]...)
+		n -= next
+		off += int64(next)
+	}
+	return buf, nil
+}
+
+type tiffdecoder struct {
+	r         io.ReaderAt
+	byteOrder binary.ByteOrder
+	config    Size
+	features  map[int][]uint
+	palette   []color.Color
+}
+
+// firstVal returns the first uint of the features entry with the given tag,
+// or 0 if the tag does not exist.
+func (d *tiffdecoder) firstVal(tag int) uint {
+	f := d.features[tag]
+	if len(f) == 0 {
+		return 0
+	}
+	return f[0]
+}
+
+// ifdUint decodes the IFD entry in p, which must be of the Byte, Short
+// or Long type, and returns the decoded uint values.
+func (d *tiffdecoder) ifdUint(p []byte) (u []uint, err error) {
+	var raw []byte
+	if len(p) < ifdLen {
+		return nil, FormatError("bad IFD entry")
+	}
+
+	datatype := d.byteOrder.Uint16(p[2:4])
+	if dt := int(datatype); dt <= 0 || dt >= len(lengths) {
+		return nil, UnsupportedError("IFD entry datatype")
+	}
+
+	count := d.byteOrder.Uint32(p[4:8])
+	if count > math.MaxInt32/lengths[datatype] {
+		return nil, FormatError("IFD data too large")
+	}
+	if datalen := lengths[datatype] * count; datalen > 4 {
+		// The IFD contains a pointer to the real value.
+		raw, err = safeReadAt(d.r, uint64(datalen), int64(d.byteOrder.Uint32(p[8:12])))
+	} else {
+		raw = p[8 : 8+datalen]
+	}
+	if err != nil {
+		return nil, err
+	}
+
+	u = make([]uint, count)
+	switch datatype {
+	case dtByte:
+		for i := uint32(0); i < count; i++ {
+			u[i] = uint(raw[i])
+		}
+	case dtShort:
+		for i := uint32(0); i < count; i++ {
+			u[i] = uint(d.byteOrder.Uint16(raw[2*i : 2*(i+1)]))
+		}
+	case dtLong:
+		for i := uint32(0); i < count; i++ {
+			u[i] = uint(d.byteOrder.Uint32(raw[4*i : 4*(i+1)]))
+		}
+	default:
+		return nil, UnsupportedError("data type")
+	}
+	return u, nil
+}
+
+// parseIFD decides whether the IFD entry in p is "interesting" and
+// stows away the data in the tiffdecoder. It returns the tag number of the
+// entry and an error, if any.
+func (d *tiffdecoder) parseIFD(p []byte) (int, error) {
+	tag := d.byteOrder.Uint16(p[0:2])
+	switch tag {
+	case tBitsPerSample,
+		tExtraSamples,
+		tPhotometricInterpretation,
+		tCompression,
+		tPredictor,
+		tStripOffsets,
+		tStripByteCounts,
+		tRowsPerStrip,
+		tTileWidth,
+		tTileLength,
+		tTileOffsets,
+		tTileByteCounts,
+		tImageLength,
+		tImageWidth,
+		tFillOrder,
+		tT4Options,
+		tT6Options:
+		val, err := d.ifdUint(p)
+		if err != nil {
+			return 0, err
+		}
+		d.features[int(tag)] = val
+	case tColorMap:
+		val, err := d.ifdUint(p)
+		if err != nil {
+			return 0, err
+		}
+		numcolors := len(val) / 3
+		if len(val)%3 != 0 || numcolors <= 0 || numcolors > 256 {
+			return 0, FormatError("bad ColorMap length")
+		}
+		d.palette = make([]color.Color, numcolors)
+		for i := 0; i < numcolors; i++ {
+			d.palette[i] = color.RGBA64{
+				uint16(val[i]),
+				uint16(val[i+numcolors]),
+				uint16(val[i+2*numcolors]),
+				0xffff,
+			}
+		}
+	case tSampleFormat:
+		// Page 27 of the spec: If the SampleFormat is present and
+		// the value is not 1 [= unsigned integer data], a Baseline
+		// TIFF reader that cannot handle the SampleFormat value
+		// must terminate the import process gracefully.
+		val, err := d.ifdUint(p)
+		if err != nil {
+			return 0, err
+		}
+		for _, v := range val {
+			if v != 1 {
+				return 0, UnsupportedError("sample format")
+			}
+		}
+	}
+	return int(tag), nil
+}
+
+func newtiffDecoder(r io.Reader) (*tiffdecoder, error) {
+	d := &tiffdecoder{
+		r:        newReaderAt(r),
+		features: make(map[int][]uint),
+	}
+
+	p := make([]byte, 8)
+	if _, err := d.r.ReadAt(p, 0); err != nil {
+		if err == io.EOF {
+			err = io.ErrUnexpectedEOF
+		}
+		return nil, err
+	}
+	switch string(p[0:4]) {
+	case leHeader:
+		d.byteOrder = binary.LittleEndian
+	case beHeader:
+		d.byteOrder = binary.BigEndian
+	default:
+		return nil, FormatError("malformed header")
+	}
+
+	ifdOffset := int64(d.byteOrder.Uint32(p[4:8]))
+
+	// The first two bytes contain the number of entries (12 bytes each).
+	if _, err := d.r.ReadAt(p[0:2], ifdOffset); err != nil {
+		return nil, err
+	}
+	numItems := int(d.byteOrder.Uint16(p[0:2]))
+
+	// All IFD entries are read in one chunk.
+	var err error
+	p, err = safeReadAt(d.r, uint64(ifdLen*numItems), ifdOffset+2)
+	if err != nil {
+		return nil, err
+	}
+
+	prevTag := -1
+	for i := 0; i < len(p); i += ifdLen {
+		tag, err := d.parseIFD(p[i : i+ifdLen])
+		if err != nil {
+			return nil, err
+		}
+		if tag <= prevTag {
+			return nil, FormatError("tags are not sorted in ascending order")
+		}
+		prevTag = tag
+	}
+
+	d.config.Width = int(d.firstVal(tImageWidth))
+	d.config.Height = int(d.firstVal(tImageLength))
+
+	return d, nil
+}
+
+// decodetiff returns the color model and dimensions of a TIFF image without
+// decoding the entire image.
+func decodetiff(r io.Reader) (Size, error) {
+	d, err := newtiffDecoder(r)
+	if err != nil {
+		return Size{}, err
+	}
+	return d.config, nil
+}
diff --git a/tiffbuf.go b/tiffbuf.go
new file mode 100644
index 0000000..c188219
--- /dev/null
+++ b/tiffbuf.go
@@ -0,0 +1,69 @@
+// 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 imgsz
+
+import "io"
+
+// buffer buffers an io.Reader to satisfy io.ReaderAt.
+type buffer struct {
+	r   io.Reader
+	buf []byte
+}
+
+// fill reads data from b.r until the buffer contains at least end bytes.
+func (b *buffer) fill(end int) error {
+	m := len(b.buf)
+	if end > m {
+		if end > cap(b.buf) {
+			newcap := 1024
+			for newcap < end {
+				newcap *= 2
+			}
+			newbuf := make([]byte, end, newcap)
+			copy(newbuf, b.buf)
+			b.buf = newbuf
+		} else {
+			b.buf = b.buf[:end]
+		}
+		if n, err := io.ReadFull(b.r, b.buf[m:end]); err != nil {
+			end = m + n
+			b.buf = b.buf[:end]
+			return err
+		}
+	}
+	return nil
+}
+
+func (b *buffer) ReadAt(p []byte, off int64) (int, error) {
+	o := int(off)
+	end := o + len(p)
+	if int64(end) != off+int64(len(p)) {
+		return 0, io.ErrUnexpectedEOF
+	}
+
+	err := b.fill(end)
+	return copy(p, b.buf[o:end]), err
+}
+
+// Slice returns a slice of the underlying buffer. The slice contains
+// n bytes starting at offset off.
+func (b *buffer) Slice(off, n int) ([]byte, error) {
+	end := off + n
+	if err := b.fill(end); err != nil {
+		return nil, err
+	}
+	return b.buf[off:end], nil
+}
+
+// newReaderAt converts an io.Reader into an io.ReaderAt.
+func newReaderAt(r io.Reader) io.ReaderAt {
+	if ra, ok := r.(io.ReaderAt); ok {
+		return ra
+	}
+	return &buffer{
+		r:   r,
+		buf: make([]byte, 0, 1024),
+	}
+}
diff --git a/tiffconsts.go b/tiffconsts.go
new file mode 100644
index 0000000..fc66b81
--- /dev/null
+++ b/tiffconsts.go
@@ -0,0 +1,64 @@
+// 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 imgsz
+
+// A tiff image file contains one or more images. The metadata
+// of each image is contained in an Image File Directory (IFD),
+// which contains entries of 12 bytes each and is described
+// on page 14-16 of the specification. An IFD entry consists of
+//
+//  - a tag, which describes the signification of the entry,
+//  - the data type and length of the entry,
+//  - the data itself or a pointer to it if it is more than 4 bytes.
+//
+// The presence of a length means that each IFD is effectively an array.
+
+const (
+	leHeader = "II\x2A\x00" // Header for little-endian files.
+	beHeader = "MM\x00\x2A" // Header for big-endian files.
+
+	ifdLen = 12 // Length of an IFD entry in bytes.
+)
+
+// Data types (p. 14-16 of the spec).
+const (
+	dtByte     = 1
+	dtASCII    = 2
+	dtShort    = 3
+	dtLong     = 4
+	dtRational = 5
+)
+
+// The length of one instance of each data type in bytes.
+var lengths = [...]uint32{0, 1, 1, 2, 4, 8}
+
+// Tags (see p. 28-41 of the spec).
+const (
+	tImageWidth                = 256
+	tImageLength               = 257
+	tBitsPerSample             = 258
+	tCompression               = 259
+	tPhotometricInterpretation = 262
+
+	tFillOrder = 266
+
+	tStripOffsets    = 273
+	tSamplesPerPixel = 277
+	tRowsPerStrip    = 278
+	tStripByteCounts = 279
+
+	tT4Options = 292 // CCITT Group 3 options, a set of 32 flag bits.
+	tT6Options = 293 // CCITT Group 4 options, a set of 32 flag bits.
+
+	tTileWidth      = 322
+	tTileLength     = 323
+	tTileOffsets    = 324
+	tTileByteCounts = 325
+
+	tPredictor    = 317
+	tColorMap     = 320
+	tExtraSamples = 338
+	tSampleFormat = 339
+)