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

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This commit is contained in:
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
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
index matches the current pixel, this index position is written to the stream.
array at the position (r * 3 + g * 5 + b * 7) % 64. In the encoder, if the pixel
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.
All values encoded in these data bits have the most significant bit (MSB) on the
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:
- QOI_INDEX -------------
- QOI_OP_INDEX ----------
| Byte[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
- QOI_RUN ---------------
| 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 ------------
- QOI_OP_DIFF -----------
| Byte[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 green 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.
- QOI_DIFF_16 -------------------------------------
- QOI_OP_LUMA -------------------------------------
| Byte[0] | Byte[1] |
| 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
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
2-bit tag b10
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
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.
- QOI_DIFF_24 ---------------------------------------------------------------
| 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 -------------
- QOI_OP_RUN ------------
| Byte[0] |
| 7 6 5 4 3 2 1 0 |
|-------------+--+--+--+--|
| 1 1 1 1 |hr|hg|hb|ha|
|-------+-----------------|
| 1 1 | run |
4-bit tag b1111
1-bit red byte follows
1-bit green byte follows
1-bit blue byte follows
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.
2-bit tag b01
6-bit run-length repeating the previous pixel: 1..62
Note that the run-lengths 63 and 64 (b111110 and b111111) are illegal as they
are occupied by the QOI_OP_RGB and QOI_OP_RGBA tags.
The byte stream is padded at the end with 4 zero bytes. Size the longest chunk
we can encounter is 5 bytes (QOI_COLOR with RGBA set), with this padding we just
have to check for an overrun once per decode loop iteration.
- QOI_OP_RGB ------------------------------------------
| Byte[0] | Byte[1] | Byte[2] | Byte[3] |
| 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)
#endif
#define QOI_INDEX 0x00 // 00xxxxxx
#define QOI_RUN 0x40 // 01xxxxxx
#define QOI_DIFF_8 0x80 // 10xxxxxx
#define QOI_DIFF_16 0xc0 // 1100xxxx
#define QOI_GDIFF_16 0xd0 // 1101xxxx
#define QOI_DIFF_24 0xe0 // 1110xxxx
#define QOI_COLOR 0xf0 // 1111xxxx
#define QOI_OP_INDEX 0x00 // 00xxxxxx
#define QOI_OP_DIFF 0x40 // 01xxxxxx
#define QOI_OP_LUMA 0x80 // 10xxxxxx
#define QOI_OP_RUN 0xc0 // 11xxxxxx
#define QOI_OP_RGB 0xfe // 11111110
#define QOI_OP_RGBA 0xff // 11111111
#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 \
(((unsigned int)'q') << 24 | ((unsigned int)'o') << 16 | \
((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);
}
else {
px.rgba.r = pixels[px_pos];
px.rgba.r = pixels[px_pos + 0];
px.rgba.g = pixels[px_pos + 1];
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 (
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;
}
@ -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;
if (index[index_pos].v == px.v) {
bytes[p++] = QOI_INDEX | index_pos;
bytes[p++] = QOI_OP_INDEX | index_pos;
}
else {
index[index_pos] = px;
if (px.rgba.a == px_prev.rgba.a) {
char vr = px.rgba.r - px_prev.rgba.r;
char vg = px.rgba.g - px_prev.rgba.g;
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_b = vb - vg;
if (
va == 0 &&
vr > -3 && vr < 2 &&
vg > -3 && vg < 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 (
va == 0 &&
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_r > -9 && vg_r < 8 &&
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++] = (vg + 32) << 3 | (vg_b + 4);
}
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);
bytes[p++] = QOI_OP_LUMA | (vg + 32);
bytes[p++] = (vg_r + 8) << 4 | (vg_b + 8);
}
else {
bytes[p++] = QOI_COLOR | (vr ? 8 : 0) | (vg ? 4 : 0) | (vb ? 2 : 0) | (va ? 1 : 0);
if (vr) { bytes[p++] = px.rgba.r; }
if (vg) { bytes[p++] = px.rgba.g; }
if (vb) { bytes[p++] = px.rgba.b; }
if (va) { bytes[p++] = px.rgba.a; }
bytes[p++] = QOI_OP_RGB;
bytes[p++] = px.rgba.r;
bytes[p++] = px.rgba.g;
bytes[p++] = px.rgba.b;
}
}
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) {
int b1 = bytes[p++];
if ((b1 & QOI_MASK_2) == QOI_INDEX) {
px = index[b1 ^ QOI_INDEX];
if (b1 == QOI_OP_RGB) {
px.rgba.r = bytes[p++];
px.rgba.g = bytes[p++];
px.rgba.b = bytes[p++];
}
else if ((b1 & QOI_MASK_2) == QOI_RUN) {
run = (b1 & 0x3f);
else if (b1 == QOI_OP_RGBA) {
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.g += ((b1 >> 2) & 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++];
px.rgba.r += (b1 & 0x0f) - 8;
px.rgba.g += (b2 >> 4) - 8;
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);
int vg = (b1 & 0x3f) - 32;
px.rgba.r += vg - 8 + ((b2 >> 4) & 0x0f);
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) {
int b2 = bytes[p++];
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++]; }
else if ((b1 & QOI_MASK_2) == QOI_OP_RUN) {
run = (b1 & 0x3f);
}
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;
}
else {
pixels[px_pos] = px.rgba.r;
pixels[px_pos + 0] = px.rgba.r;
pixels[px_pos + 1] = px.rgba.g;
pixels[px_pos + 2] = px.rgba.b;
}