diff --git a/qoi.h b/qoi.h index a16262f..8bd8126 100644 --- a/qoi.h +++ b/qoi.h @@ -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')) @@ -400,9 +383,9 @@ 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.g = pixels[px_pos+1]; - px.rgba.b = pixels[px_pos+2]; + px.rgba.r = pixels[px_pos + 0]; + px.rgba.g = pixels[px_pos + 1]; + px.rgba.b = pixels[px_pos + 2]; } if (px.v == px_prev.v) { @@ -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; - 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; + 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 vg_r = vr - vg; - char vg_b = vb - vg; + 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); - } - 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 > -33 && vg < 32 && - vg_b > -5 && vg_b < 4 - ) { - 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); + if ( + vr > -3 && vr < 2 && + vg > -3 && vg < 2 && + vb > -3 && vb < 2 + ) { + bytes[p++] = QOI_OP_DIFF | ((vr + 2) << 4) | (vg + 2) << 2 | (vb + 2); + } + else if ( + vg_r > -9 && vg_r < 8 && + vg > -33 && vg < 32 && + vg_b > -9 && vg_b < 8 + ) { + bytes[p++] = QOI_OP_LUMA | (vg + 32); + bytes[p++] = (vg_r + 8) << 4 | (vg_b + 8); + } + else { + bytes[p++] = QOI_OP_RGB; + bytes[p++] = px.rgba.r; + bytes[p++] = px.rgba.g; + bytes[p++] = px.rgba.b; + } } 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_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; @@ -584,9 +544,9 @@ 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+1] = px.rgba.g; - pixels[px_pos+2] = px.rgba.b; + pixels[px_pos + 0] = px.rgba.r; + pixels[px_pos + 1] = px.rgba.g; + pixels[px_pos + 2] = px.rgba.b; } }