Allow for intra-byte bits_per_sample. #218
Open
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Specifically, correctly read stripped tifs for any bits_per_sample sized up to the normal maximum bits_per_sample limit. Also, correctly read tiled tiffs that have bit padding in the last tile of each row. Bit padding in more than one tile per row is not supported. Future work could include error reporting about gaps in coverage, tests, and a separate newtype for buffer indexing (vs usize for bytes)
fintelia
reviewed
Nov 13, 2023
| fn usize_div_ceil(numerator: usize, denominator: usize) -> usize { | ||
| (numerator + denominator - 1) / denominator | ||
| } | ||
|
|
There was a problem hiding this comment.
Could you add a comment here explaining what a "buffer unit" is? Though a shorter name might be better. Maybe call them "elements"?
| if output_width == data_dims.0 as usize && padding_right == 0 { | ||
| let total_samples = data_dims.0 as usize * data_dims.1 as usize * samples; | ||
| let tile = &mut buffer.as_bytes_mut()[..total_samples * byte_len]; | ||
| let row_buffer_units: usize = usize_div_ceil(data_dims.0 as usize * samples * self.bits_per_sample as usize, byte_len * 8); |
There was a problem hiding this comment.
I'm nervous about overflowing a usize here. I know the old code isn't careful here either, but it would be good to address. (Especially now that there's an additional multiplication by bits_per_sample that makes it even easier to overflow on a 32-bit system).
Probably the right thing to do would be to do most of the arithmetic using u64's and then use try_into when converting back.
| /// If we leave in per-tile bit padding, then we cannot do it without knowing the number of tiles across this image is. | ||
| /// | ||
| /// We have two options basically for precise allocation without knowing the number of tiles across: | ||
| /// * Ban tiles where tile_dim % (bits_per_sample * samples) == 0 |
There was a problem hiding this comment.
Could you add a check if this condition isn't met, and return an unsupported error in that case?
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Specifically, correctly read stripped tifs for any bits_per_sample sized up to the normal maximum bits_per_sample limit. Also, correctly read tiled tiffs that have bit padding in the last tile of each row. Bit padding in more than one tile per row is not supported.
Future work could include error reporting about gaps in coverage, tests, and a separate newtype for buffer indexing (vs usize for bytes)
Addresses #217; here are the caveats/support:
(samples*bits_per_sample*tile_width)%byte_lenmust be 0. Since tile dimensions are supposed to be multiples of 16, that means 1,2 and 4 bits_per_sample should always work. Other values may work correctly depending on the tile size and samples_per_pixel combination.