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Remove QOI_DIFF_16 and QOI_DIFF_24; better tagging of remaining ops; better hash function

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Dominic Szablewski 2021-12-06 21:23:13 +01:00
parent 66d12eb078
commit 28954f7a9a
1 changed files with 121 additions and 161 deletions
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246
qoi.h
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@ -102,17 +102,23 @@ pixel value. Pixels are either encoded as
A running array[64] of previously seen pixel values is maintained by the encoder A running array[64] of previously seen pixel values is maintained by the encoder
and decoder. Each pixel that is seen by the encoder and decoder is put into this and decoder. Each pixel that is seen by the encoder and decoder is put into this
array at the position (r^g^b^a) % 64. In the encoder, if the pixel value at this array at the position (r * 3 + g * 5 + b * 7) % 64. In the encoder, if the pixel
index matches the current pixel, this index position is written to the stream. value at this index matches the current pixel, this index position is written to
the stream.
Each chunk starts with a 2, 3 or 4 bit tag, followed by a number of data bits. Each chunk starts with a 8 or 2 bit tag, followed by a number of data bits.
The bit length of chunks is divisible by 8 - i.e. all chunks are byte aligned. The bit length of chunks is divisible by 8 - i.e. all chunks are byte aligned.
All values encoded in these data bits have the most significant bit (MSB) on the All values encoded in these data bits have the most significant bit (MSB) on the
left. left.
The 8-bit tags have precedence over the 2-bit tags. A decoder must check the
8-bit tags first.
The possible chunks are: The possible chunks are:
- QOI_INDEX -------------
- QOI_OP_INDEX ----------
| Byte[0] | | Byte[0] |
| 7 6 5 4 3 2 1 0 | | 7 6 5 4 3 2 1 0 |
|-------+-----------------| |-------+-----------------|
@ -122,23 +128,13 @@ The possible chunks are:
6-bit index into the color index array: 0..63 6-bit index into the color index array: 0..63
- QOI_RUN --------------- - QOI_OP_DIFF -----------
| Byte[0] |
| 7 6 5 4 3 2 1 0 |
|-------+-----------------|
| 0 1 | run |
2-bit tag b01
6-bit run-length repeating the previous pixel: 1..64
- QOI_DIFF_8 ------------
| Byte[0] | | Byte[0] |
| 7 6 5 4 3 2 1 0 | | 7 6 5 4 3 2 1 0 |
|-------+-----+-----+-----| |-------+-----+-----+-----|
| 1 0 | dr | db | bg | | 0 1 | dr | dg | db |
2-bit tag b10 2-bit tag b01
2-bit red channel difference from the previous pixel between -2..1 2-bit red channel difference from the previous pixel between -2..1
2-bit green channel difference from the previous pixel between -2..1 2-bit green channel difference from the previous pixel between -2..1
2-bit blue channel difference from the previous pixel between -2..1 2-bit blue channel difference from the previous pixel between -2..1
@ -147,31 +143,16 @@ The difference to the current channel values are using a wraparound operation,
so "1 - 2" will result in 255, while "255 + 1" will result in 0. so "1 - 2" will result in 255, while "255 + 1" will result in 0.
- QOI_DIFF_16 ------------------------------------- - QOI_OP_LUMA -------------------------------------
| Byte[0] | Byte[1] | | Byte[0] | Byte[1] |
| 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 | | 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 |
|-------------+-----------|------------ +-----------| |-------+-----------------+-------------+-----------|
| 1 1 0 0 | red diff | green diff | blue diff | | 1 0 | green diff | dr - dg | db - dg |
4-bit tag b1100 2-bit tag b10
4-bit red channel difference from the previous pixel between -8..7
4-bit green channel difference from the previous pixel between -8..7
4-bit blue channel difference from the previous pixel between -8..7
The difference to the current channel values are using a wraparound operation,
so "5 - 8" will result in 253, while "250 + 7" will result in 1.
- QOI_GDIFF_16 ------------------------------------
| Byte[0] | Byte[1] |
| 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 |
|-------------+--------+-------------------+--------|
| 1 1 0 1 | dr-dg | green diff | db-dg |
4-bit tag b1101
3-bit red channel difference minus green channel difference -4..3
6-bit green channel difference from the previous pixel -32..31 6-bit green channel difference from the previous pixel -32..31
3-bit blue channel difference minus green channel difference -4..3 4-bit red channel difference minus green channel difference -8..7
4-bit blue channel difference minus green channel difference -8..7
The green channel is used to indicate the general direction of change and gets The green channel is used to indicate the general direction of change and gets
a few more bits. dr and db base their diffs off of the green channel diff. E.g. a few more bits. dr and db base their diffs off of the green channel diff. E.g.
@ -181,42 +162,46 @@ The difference to the current channel values are using a wraparound operation,
so "10 - 13" will result in 253, while "250 + 7" will result in 1. so "10 - 13" will result in 253, while "250 + 7" will result in 1.
- QOI_DIFF_24 --------------------------------------------------------------- - QOI_OP_RUN ------------
| Byte[0] | Byte[1] | Byte[2] |
| 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 |
|-------------+----------------+--------------+----------------+--------------|
| 1 1 1 0 | red diff | green diff | blue diff | alpha diff |
4-bit tag b1110
5-bit red channel difference from the previous pixel between -16..15
5-bit green channel difference from the previous pixel between -16..15
5-bit blue channel difference from the previous pixel between -16..15
5-bit alpha channel difference from the previous pixel between -16..15
The difference to the current channel values are using a wraparound operation,
so "10 - 13" will result in 253, while "250 + 7" will result in 1.
- QOI_COLOR -------------
| Byte[0] | | Byte[0] |
| 7 6 5 4 3 2 1 0 | | 7 6 5 4 3 2 1 0 |
|-------------+--+--+--+--| |-------+-----------------|
| 1 1 1 1 |hr|hg|hb|ha| | 1 1 | run |
4-bit tag b1111 2-bit tag b01
1-bit red byte follows 6-bit run-length repeating the previous pixel: 1..62
1-bit green byte follows Note that the run-lengths 63 and 64 (b111110 and b111111) are illegal as they
1-bit blue byte follows are occupied by the QOI_OP_RGB and QOI_OP_RGBA tags.
1-bit alpha byte follows
For each set bit hr, hg, hb and ha another byte follows in this order. If such a
byte follows, it will replace the current color channel value with the value of
this byte.
The byte stream is padded at the end with 4 zero bytes. Size the longest chunk - QOI_OP_RGB ------------------------------------------
we can encounter is 5 bytes (QOI_COLOR with RGBA set), with this padding we just | Byte[0] | Byte[1] | Byte[2] | Byte[3] |
have to check for an overrun once per decode loop iteration. | 7 6 5 4 3 2 1 0 | 7 .. 0 | 7 .. 0 | 7 .. 0 |
|-------------------------+---------+---------+---------|
| 1 1 1 1 1 1 1 0 | red | green | blue |
8-bit tag b11111110
8-bit red channel value
8-bit green channel value
8-bit blue channel value
- QOI_OP_RGBA ----------------------------------------------------
| Byte[0] | Byte[1] | Byte[2] | Byte[3] | Byte[4] |
| 7 6 5 4 3 2 1 0 | 7 .. 0 | 7 .. 0 | 7 .. 0 | 7 .. 0 |
|-------------------------+---------+---------+---------+---------|
| 1 1 1 1 1 1 1 1 | red | green | blue | alpha |
8-bit tag b11111111
8-bit red channel value
8-bit green channel value
8-bit blue channel value
8-bit alpha channel value
The byte stream is padded at the end with 4 zero bytes. Size the longest legal
chunk is 5 bytes (QOI_OP_RGBA), with this padding it is possible to check for an
overrun only once per decode loop iteration.
*/ */
@ -318,18 +303,16 @@ void *qoi_decode(const void *data, int size, qoi_desc *desc, int channels);
#define QOI_FREE(p) free(p) #define QOI_FREE(p) free(p)
#endif #endif
#define QOI_INDEX 0x00 // 00xxxxxx #define QOI_OP_INDEX 0x00 // 00xxxxxx
#define QOI_RUN 0x40 // 01xxxxxx #define QOI_OP_DIFF 0x40 // 01xxxxxx
#define QOI_DIFF_8 0x80 // 10xxxxxx #define QOI_OP_LUMA 0x80 // 10xxxxxx
#define QOI_DIFF_16 0xc0 // 1100xxxx #define QOI_OP_RUN 0xc0 // 11xxxxxx
#define QOI_GDIFF_16 0xd0 // 1101xxxx #define QOI_OP_RGB 0xfe // 11111110
#define QOI_DIFF_24 0xe0 // 1110xxxx #define QOI_OP_RGBA 0xff // 11111111
#define QOI_COLOR 0xf0 // 1111xxxx
#define QOI_MASK_2 0xc0 // 11000000 #define QOI_MASK_2 0xc0 // 11000000
#define QOI_MASK_4 0xf0 // 11110000
#define QOI_COLOR_HASH(C) (C.rgba.r ^ C.rgba.g ^ C.rgba.b ^ C.rgba.a) #define QOI_COLOR_HASH(C) (C.rgba.r * 3 + C.rgba.g * 5 + C.rgba.b * 7)
#define QOI_MAGIC \ #define QOI_MAGIC \
(((unsigned int)'q') << 24 | ((unsigned int)'o') << 16 | \ (((unsigned int)'q') << 24 | ((unsigned int)'o') << 16 | \
((unsigned int)'i') << 8 | ((unsigned int)'f')) ((unsigned int)'i') << 8 | ((unsigned int)'f'))
@ -400,7 +383,7 @@ void *qoi_encode(const void *data, const qoi_desc *desc, int *out_len) {
px = *(qoi_rgba_t *)(pixels + px_pos); px = *(qoi_rgba_t *)(pixels + px_pos);
} }
else { else {
px.rgba.r = pixels[px_pos]; px.rgba.r = pixels[px_pos + 0];
px.rgba.g = pixels[px_pos + 1]; px.rgba.g = pixels[px_pos + 1];
px.rgba.b = pixels[px_pos + 2]; px.rgba.b = pixels[px_pos + 2];
} }
@ -411,9 +394,9 @@ void *qoi_encode(const void *data, const qoi_desc *desc, int *out_len) {
if ( if (
run > 0 && run > 0 &&
(run == 64 || px.v != px_prev.v || px_pos == px_end) (run == 62 || px.v != px_prev.v || px_pos == px_end)
) { ) {
bytes[p++] = QOI_RUN | (run - 1); bytes[p++] = QOI_OP_RUN | (run - 1);
run = 0; run = 0;
} }
@ -421,61 +404,47 @@ void *qoi_encode(const void *data, const qoi_desc *desc, int *out_len) {
int index_pos = QOI_COLOR_HASH(px) % 64; int index_pos = QOI_COLOR_HASH(px) % 64;
if (index[index_pos].v == px.v) { if (index[index_pos].v == px.v) {
bytes[p++] = QOI_INDEX | index_pos; bytes[p++] = QOI_OP_INDEX | index_pos;
} }
else { else {
index[index_pos] = px; index[index_pos] = px;
if (px.rgba.a == px_prev.rgba.a) {
char vr = px.rgba.r - px_prev.rgba.r; char vr = px.rgba.r - px_prev.rgba.r;
char vg = px.rgba.g - px_prev.rgba.g; char vg = px.rgba.g - px_prev.rgba.g;
char vb = px.rgba.b - px_prev.rgba.b; char vb = px.rgba.b - px_prev.rgba.b;
char va = px.rgba.a - px_prev.rgba.a;
char vg_r = vr - vg; char vg_r = vr - vg;
char vg_b = vb - vg; char vg_b = vb - vg;
if ( if (
va == 0 &&
vr > -3 && vr < 2 && vr > -3 && vr < 2 &&
vg > -3 && vg < 2 && vg > -3 && vg < 2 &&
vb > -3 && vb < 2 vb > -3 && vb < 2
) { ) {
bytes[p++] = QOI_DIFF_8 | ((vr + 2) << 4) | (vg + 2) << 2 | (vb + 2); bytes[p++] = QOI_OP_DIFF | ((vr + 2) << 4) | (vg + 2) << 2 | (vb + 2);
} }
else if ( else if (
va == 0 && vg_r > -9 && vg_r < 8 &&
vr > -9 && vr < 8 &&
vg > -9 && vg < 8 &&
vb > -9 && vb < 8
) {
bytes[p++] = QOI_DIFF_16 | (vr + 8);
bytes[p++] = (vg + 8) << 4 | (vb + 8);
}
else if (
va == 0 &&
vg_r > -5 && vg_r < 4 &&
vg > -33 && vg < 32 && vg > -33 && vg < 32 &&
vg_b > -5 && vg_b < 4 vg_b > -9 && vg_b < 8
) { ) {
bytes[p++] = QOI_GDIFF_16 | (vg_r + 4) << 1 | (vg + 32) >> 5; bytes[p++] = QOI_OP_LUMA | (vg + 32);
bytes[p++] = (vg + 32) << 3 | (vg_b + 4); bytes[p++] = (vg_r + 8) << 4 | (vg_b + 8);
}
else if (
vr > -17 && vr < 16 &&
vg > -17 && vg < 16 &&
vb > -17 && vb < 16 &&
va > -17 && va < 16
) {
bytes[p++] = QOI_DIFF_24 | (vr + 16) >> 1;
bytes[p++] = (vr + 16) << 7 | (vg + 16) << 2 | (vb + 16) >> 3;
bytes[p++] = (vb + 16) << 5 | (va + 16);
} }
else { else {
bytes[p++] = QOI_COLOR | (vr ? 8 : 0) | (vg ? 4 : 0) | (vb ? 2 : 0) | (va ? 1 : 0); bytes[p++] = QOI_OP_RGB;
if (vr) { bytes[p++] = px.rgba.r; } bytes[p++] = px.rgba.r;
if (vg) { bytes[p++] = px.rgba.g; } bytes[p++] = px.rgba.g;
if (vb) { bytes[p++] = px.rgba.b; } bytes[p++] = px.rgba.b;
if (va) { bytes[p++] = px.rgba.a; } }
}
else {
bytes[p++] = QOI_OP_RGBA;
bytes[p++] = px.rgba.r;
bytes[p++] = px.rgba.g;
bytes[p++] = px.rgba.b;
bytes[p++] = px.rgba.a;
} }
} }
} }
@ -538,43 +507,34 @@ void *qoi_decode(const void *data, int size, qoi_desc *desc, int channels) {
else if (p < chunks_len) { else if (p < chunks_len) {
int b1 = bytes[p++]; int b1 = bytes[p++];
if ((b1 & QOI_MASK_2) == QOI_INDEX) { if (b1 == QOI_OP_RGB) {
px = index[b1 ^ QOI_INDEX]; px.rgba.r = bytes[p++];
px.rgba.g = bytes[p++];
px.rgba.b = bytes[p++];
} }
else if ((b1 & QOI_MASK_2) == QOI_RUN) { else if (b1 == QOI_OP_RGBA) {
run = (b1 & 0x3f); px.rgba.r = bytes[p++];
px.rgba.g = bytes[p++];
px.rgba.b = bytes[p++];
px.rgba.a = bytes[p++];
} }
else if ((b1 & QOI_MASK_2) == QOI_DIFF_8) { else if ((b1 & QOI_MASK_2) == QOI_OP_INDEX) {
px = index[b1 ^ QOI_OP_INDEX];
}
else if ((b1 & QOI_MASK_2) == QOI_OP_DIFF) {
px.rgba.r += ((b1 >> 4) & 0x03) - 2; px.rgba.r += ((b1 >> 4) & 0x03) - 2;
px.rgba.g += ((b1 >> 2) & 0x03) - 2; px.rgba.g += ((b1 >> 2) & 0x03) - 2;
px.rgba.b += ( b1 & 0x03) - 2; px.rgba.b += ( b1 & 0x03) - 2;
} }
else if ((b1 & QOI_MASK_4) == QOI_DIFF_16) { else if ((b1 & QOI_MASK_2) == QOI_OP_LUMA) {
int b2 = bytes[p++]; int b2 = bytes[p++];
px.rgba.r += (b1 & 0x0f) - 8; int vg = (b1 & 0x3f) - 32;
px.rgba.g += (b2 >> 4) - 8; px.rgba.r += vg - 8 + ((b2 >> 4) & 0x0f);
px.rgba.b += (b2 & 0x0f) - 8;
}
else if ((b1 & QOI_MASK_4) == QOI_GDIFF_16) {
int b2 = bytes[p++];
int vg = ((b1 & 0x01) << 5 | (b2 & 0xf8) >> 3) - 32;
px.rgba.r += vg - 4 + ((b1 & 0x0e) >> 1);
px.rgba.g += vg; px.rgba.g += vg;
px.rgba.b += vg - 4 + (b2 & 0x07); px.rgba.b += vg - 8 + (b2 & 0x0f);
} }
else if ((b1 & QOI_MASK_4) == QOI_DIFF_24) { else if ((b1 & QOI_MASK_2) == QOI_OP_RUN) {
int b2 = bytes[p++]; run = (b1 & 0x3f);
int b3 = bytes[p++];
px.rgba.r += (((b1 & 0x0f) << 1) | (b2 >> 7)) - 16;
px.rgba.g += ((b2 & 0x7c) >> 2) - 16;
px.rgba.b += (((b2 & 0x03) << 3) | ((b3 & 0xe0) >> 5)) - 16;
px.rgba.a += (b3 & 0x1f) - 16;
}
else if ((b1 & QOI_MASK_4) == QOI_COLOR) {
if (b1 & 8) { px.rgba.r = bytes[p++]; }
if (b1 & 4) { px.rgba.g = bytes[p++]; }
if (b1 & 2) { px.rgba.b = bytes[p++]; }
if (b1 & 1) { px.rgba.a = bytes[p++]; }
} }
index[QOI_COLOR_HASH(px) % 64] = px; index[QOI_COLOR_HASH(px) % 64] = px;
@ -584,7 +544,7 @@ void *qoi_decode(const void *data, int size, qoi_desc *desc, int channels) {
*(qoi_rgba_t*)(pixels + px_pos) = px; *(qoi_rgba_t*)(pixels + px_pos) = px;
} }
else { else {
pixels[px_pos] = px.rgba.r; pixels[px_pos + 0] = px.rgba.r;
pixels[px_pos + 1] = px.rgba.g; pixels[px_pos + 1] = px.rgba.g;
pixels[px_pos + 2] = px.rgba.b; pixels[px_pos + 2] = px.rgba.b;
} }