Difference between revisions of "RLEp"
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| − | The RLEp format is a variant of the RLE compression (Run-length encoding) with the particularity of having 2 bits reserved to encode a pattern type and 6 bits for its length. | + | The '''RLEp''' format is a variant of the RLE compression ([https://en.wikipedia.org/wiki/Run-length_encoding Run-length encoding]) with the particularity of having 2 bits reserved to encode a pattern type and 6 bits for its length (max length is 64 bytes per pattern). |
Pattern types: | Pattern types: | ||
{| class="wikitable" | {| class="wikitable" | ||
| − | ! Val !! Name !! Desc. | + | ! Val !! Name !! Min len !! Desc. |
|- | |- | ||
| − | | <tt>[00¦len]</tt> || Default value || Repeat default value <tt>len</tt> times. The default value is either 0 or the first byte of the RLEp code. | + | | <tt>[00¦len]</tt> || Default value || 2 || Repeat default value <tt>len</tt> times. The default value is either 0 or the first byte of the RLEp code. |
|- | |- | ||
| − | | <tt>[01¦len][value]</tt> || 1 byte || Repeat the next character <tt>len</tt> times. | + | | <tt>[01¦len][value]</tt> || 1 byte || 2 || Repeat the next character <tt>len</tt> times. |
|- | |- | ||
| − | | <tt>[10¦len][value][value]</tt> || 2 bytes || Repeat the next two characters <tt>len</tt> times. | + | | <tt>[10¦len][value][value]</tt> || 2 bytes || 2 || Repeat the next two characters <tt>len</tt> times. |
|- | |- | ||
| − | | <tt>[11¦len][value][value]...</tt> || Uncompress || Followed by a list of non-compressed bytes of size <tt>len</tt>. | + | | <tt>[11¦len][value][value]...</tt> || Uncompress || 0 || Followed by a list of non-compressed bytes of size <tt>len</tt>. |
|} | |} | ||
| + | |||
| + | The efficiency of RLEp encoding is highly data-dependent. Data with "holes" or repetitions, such as sprites, can have a very good compression ratio, whereas a bitmap image teeming with detail will have a very poor (or even negative) compression ratio. | ||
[[Category:Format]] | [[Category:Format]] | ||
Latest revision as of 00:11, 16 December 2023
The RLEp format is a variant of the RLE compression (Run-length encoding) with the particularity of having 2 bits reserved to encode a pattern type and 6 bits for its length (max length is 64 bytes per pattern).
Pattern types:
| Val | Name | Min len | Desc. |
|---|---|---|---|
| [00¦len] | Default value | 2 | Repeat default value len times. The default value is either 0 or the first byte of the RLEp code. |
| [01¦len][value] | 1 byte | 2 | Repeat the next character len times. |
| [10¦len][value][value] | 2 bytes | 2 | Repeat the next two characters len times. |
| [11¦len][value][value]... | Uncompress | 0 | Followed by a list of non-compressed bytes of size len. |
The efficiency of RLEp encoding is highly data-dependent. Data with "holes" or repetitions, such as sprites, can have a very good compression ratio, whereas a bitmap image teeming with detail will have a very poor (or even negative) compression ratio.