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59 lines
1.6 KiB
Markdown
59 lines
1.6 KiB
Markdown
# TREZOR Optimized Image Format
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All multibyte integer values are little endian!
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## Header
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| offset | length | name | description |
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|-------:|-------:|------|-------------|
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| 0x0000 | 3 | magic | `TOI` |
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| 0x0003 | 1 | fmt | data format: `f` or `g` (see below) |
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| 0x0004 | 2 | width | width of the image |
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| 0x0006 | 2 | height | height of the image |
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| 0x0008 | 4 | datasize | length of the compressed data |
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| 0x000A | ? | data | compressed data (see below) |
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## Format
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TOI currently supports 2 variants:
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* `f`: full-color, file extension `.toif`
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* `g`: gray-scale, file extension `.toig`
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### Full-color
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For each pixel a 16-bit value is used.
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First 5 bits are used for red component, next 6 bits are green,
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final 5 bits are blue:
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| 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
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|----|----|----|----|----|----|---|---|---|---|---|---|---|---|---|---|
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| R | R | R | R | R | G | G | G | G | G | G | B | B | B | B | B |
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### Gray-scale
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Each pixel is encoded using a 4-bit value.
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Each byte contains color of two pixels:
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| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
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|---|---|---|---|---|---|---|---|
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| Po | Po | Po | Po | Pe | Pe | Pe | Pe |
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Where Po is odd pixel and Pe is even pixel.
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## Compression
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Pixel data is compressed using DEFLATE algorithm with 10-bit sliding window
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and no header. This can be achieved with ZLIB library by using the following:
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```python
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import zlib
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z = zlib.compressobj(level=9, wbits=10)
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zdata = z.compress(pixeldata) + z.flush()
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zdata = zdata[2:-4] # strip header and checksum
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```
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## Tools
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* [png2toi](../tools/png2toi) - tool for converting PNG into TOI format
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