Merge pull request #43 from MasterQ32/improved_docs
Documentation improval
This commit is contained in:
Dominic Szablewski
GitHub
commit
bdfda4a5f6
117
qoi.h
117
qoi.h
@ -109,54 +109,87 @@ 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 2, 3 or 4 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.
|
||||||
|
|
||||||
QOI_INDEX {
|
The possible chunks are:
|
||||||
u8 tag : 2; // b00
|
|
||||||
u8 idx : 6; // 6-bit index into the color index array: 0..63
|
|
||||||
}
|
|
||||||
|
|
||||||
QOI_RUN_8 {
|
| QOI_INDEX |
|
||||||
u8 tag : 3; // b010
|
| Byte + 0 |
|
||||||
u8 run : 5; // 5-bit run-length repeating the previous pixel: 1..32
|
| 7 6 5 4 3 2 1 0 |
|
||||||
}
|
|-------------------------|
|
||||||
|
| 0 0 i5 i4 i3 i2 i1 i0 |
|
||||||
|
|
||||||
QOI_RUN_16 {
|
i5...i0 forming the 6-bit index into the color index array: 0..63
|
||||||
u8 tag : 3; // b011
|
|
||||||
u16 run : 13; // 13-bit run-length repeating the previous pixel: 33..8224
|
|
||||||
}
|
|
||||||
|
|
||||||
QOI_DIFF_8 {
|
|
||||||
u8 tag : 2; // b10
|
|
||||||
u8 dr : 2; // 2-bit red channel difference: -2..1
|
|
||||||
u8 dg : 2; // 2-bit green channel difference: -2..1
|
|
||||||
u8 db : 2; // 2-bit blue channel difference: -2..1
|
|
||||||
}
|
|
||||||
|
|
||||||
QOI_DIFF_16 {
|
| QOI_INDEX |
|
||||||
u8 tag : 3; // b110
|
| Byte + 0 |
|
||||||
u8 dr : 5; // 5-bit red channel difference: -16..15
|
| 7 6 5 4 3 2 1 0 |
|
||||||
u8 dg : 4; // 4-bit green channel difference: -8.. 7
|
|-------------------------|
|
||||||
u8 db : 4; // 4-bit blue channel difference: -8.. 7
|
| 0 1 0 i4 i3 i2 i1 i0 |
|
||||||
}
|
|
||||||
|
|
||||||
QOI_DIFF_24 {
|
i4...i0 forming the 5-bit run-length repeating the previous pixel: 1..32
|
||||||
u8 tag : 4; // b1110
|
|
||||||
u8 dr : 5; // 5-bit red channel difference: -16..15
|
|
||||||
u8 dg : 5; // 5-bit green channel difference: -16..15
|
| QOI_RUN_16 |
|
||||||
u8 db : 5; // 5-bit blue channel difference: -16..15
|
| Byte + 0 | Byte + 1 |
|
||||||
u8 da : 5; // 5-bit alpha channel difference: -16..15
|
| 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 |
|
||||||
}
|
|--------------------------------|-------------------------|
|
||||||
|
| 0 1 1 r12 r11 r10 r9 r8 | r7 r6 r5 r4 r3 r2 r1 r0 |
|
||||||
|
|
||||||
|
r12...r0 forming the 13-bit run-length repeating the previous pixel: 33..8224
|
||||||
|
|
||||||
|
|
||||||
|
| QOI_DIFF_8 |
|
||||||
|
| Byte + 0 |
|
||||||
|
| 7 6 5 4 3 2 1 0 |
|
||||||
|
|-------------------------|
|
||||||
|
| 1 0 r1 r0 g1 g0 b1 b0 |
|
||||||
|
|
||||||
|
r1...r0 forming the red channel difference between -2..1
|
||||||
|
g1...g0 forming the green channel difference between -2..1
|
||||||
|
b1...b0 forming the blue channel difference between -2..1
|
||||||
|
|
||||||
|
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 |
|
||||||
|
| Byte + 0 | Byte + 1 |
|
||||||
|
| 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 |
|
||||||
|
|-------------------------|-------------------------|
|
||||||
|
| 1 1 0 r4 r3 r2 r1 r0 | g3 g2 g1 g0 b3 b2 b1 b0 |
|
||||||
|
|
||||||
|
r4...r0 forming the red channel difference between -16..15
|
||||||
|
g3...g0 forming the green channel difference between -8..7
|
||||||
|
b3...b0 forming the blue channel difference between -8..7
|
||||||
|
|
||||||
|
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 + 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 |
|
||||||
|
|-------------------------|-------------------------|-------------------------|
|
||||||
|
| 1 1 1 0 r4 r3 r2 r1 | r0 g4 g3 g2 g1 g0 b4 b3 | b2 b1 b0 a4 a3 a2 a1 a0 |
|
||||||
|
|
||||||
|
r4...r0 forming the red channel difference between -16..15
|
||||||
|
g4...g0 forming the green channel difference between -16..15
|
||||||
|
b4...b0 forming the blue channel difference between -16..15
|
||||||
|
a4...a0 forming the alpha channel difference 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 |
|
||||||
|
| 7 6 5 4 3 2 1 0 |
|
||||||
|
|-------------------------|
|
||||||
|
| 1 1 1 1 r g b a |
|
||||||
|
|
||||||
|
for each set bit r, g, b and a another byte follows in the order written here. If such a byte follows,
|
||||||
|
it will replace the current color channel value with the value of this byte.
|
||||||
|
|
||||||
QOI_COLOR {
|
|
||||||
u8 tag : 4; // b1111
|
|
||||||
u8 has_r: 1; // red byte follows
|
|
||||||
u8 has_g: 1; // green byte follows
|
|
||||||
u8 has_b: 1; // blue byte follows
|
|
||||||
u8 has_a: 1; // alpha byte follows
|
|
||||||
u8 r; // red value if has_r == 1: 0..255
|
|
||||||
u8 g; // green value if has_g == 1: 0..255
|
|
||||||
u8 b; // blue value if has_b == 1: 0..255
|
|
||||||
u8 a; // alpha value if has_a == 1: 0..255
|
|
||||||
}
|
|
||||||
|
|
||||||
The byte stream is padded with 4 zero bytes. Size the longest chunk we can
|
The byte stream is padded 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
|
encounter is 5 bytes (QOI_COLOR with RGBA set), with this padding we just have
|
||||||
|
|||||||
Loading…
Reference in New Issue
Block a user