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//! Decoding of OpenEXR (.exr) Images
//!
//! OpenEXR is an image format that is widely used, especially in VFX,
//! because it supports lossless and lossy compression for float data.
//!
//! This decoder only supports RGB and RGBA images.
//! If an image does not contain alpha information,
//! it is defaulted to `1.0` (no transparency).
//!
//! # Related Links
//! * <https://www.openexr.com/documentation.html> - The OpenEXR reference.
//!
//!
//! Current limitations (July 2021):
//! - only pixel type `Rgba32F` and `Rgba16F` are supported
//! - only non-deep rgb/rgba files supported, no conversion from/to YCbCr or similar
//! - only the first non-deep rgb layer is used
//! - only the largest mip map level is used
//! - pixels outside display window are lost
//! - meta data is lost
//! - dwaa/dwab compressed images not supported yet by the exr library
//! - (chroma) subsampling not supported yet by the exr library
use exr::prelude::*;
use crate::error::{DecodingError, EncodingError, ImageFormatHint};
use crate::image::decoder_to_vec;
use crate::{
ColorType, ExtendedColorType, ImageDecoder, ImageEncoder, ImageError, ImageFormat, ImageResult,
Progress,
};
use std::convert::TryInto;
use std::io::{Cursor, Read, Seek, Write};
/// An OpenEXR decoder. Immediately reads the meta data from the file.
#[derive(Debug)]
pub struct OpenExrDecoder<R> {
exr_reader: exr::block::reader::Reader<R>,
// select a header that is rgb and not deep
header_index: usize,
// decode either rgb or rgba.
// can be specified to include or discard alpha channels.
// if none, the alpha channel will only be allocated where the file contains data for it.
alpha_preference: Option<bool>,
alpha_present_in_file: bool,
}
impl<R: Read + Seek> OpenExrDecoder<R> {
/// Create a decoder. Consumes the first few bytes of the source to extract image dimensions.
/// Assumes the reader is buffered. In most cases,
/// you should wrap your reader in a `BufReader` for best performance.
/// Loads an alpha channel if the file has alpha samples.
/// Use `with_alpha_preference` if you want to load or not load alpha unconditionally.
pub fn new(source: R) -> ImageResult<Self> {
Self::with_alpha_preference(source, None)
}
/// Create a decoder. Consumes the first few bytes of the source to extract image dimensions.
/// Assumes the reader is buffered. In most cases,
/// you should wrap your reader in a `BufReader` for best performance.
/// If alpha preference is specified, an alpha channel will
/// always be present or always be not present in the returned image.
/// If alpha preference is none, the alpha channel will only be returned if it is found in the file.
pub fn with_alpha_preference(source: R, alpha_preference: Option<bool>) -> ImageResult<Self> {
// read meta data, then wait for further instructions, keeping the file open and ready
let exr_reader = exr::block::read(source, false).map_err(to_image_err)?;
let header_index = exr_reader
.headers()
.iter()
.position(|header| {
// check if r/g/b exists in the channels
let has_rgb = ["R", "G", "B"]
.iter()
.all(|&required| // alpha will be optional
header.channels.find_index_of_channel(&Text::from(required)).is_some());
// we currently dont support deep images, or images with other color spaces than rgb
!header.deep && has_rgb
})
.ok_or_else(|| {
ImageError::Decoding(DecodingError::new(
ImageFormatHint::Exact(ImageFormat::OpenExr),
"image does not contain non-deep rgb channels",
))
})?;
let has_alpha = exr_reader.headers()[header_index]
.channels
.find_index_of_channel(&Text::from("A"))
.is_some();
Ok(Self {
alpha_preference,
exr_reader,
header_index,
alpha_present_in_file: has_alpha,
})
}
// does not leak exrs-specific meta data into public api, just does it for this module
fn selected_exr_header(&self) -> &exr::meta::header::Header {
&self.exr_reader.meta_data().headers[self.header_index]
}
}
impl<'a, R: 'a + Read + Seek> ImageDecoder<'a> for OpenExrDecoder<R> {
type Reader = Cursor<Vec<u8>>;
fn dimensions(&self) -> (u32, u32) {
let size = self
.selected_exr_header()
.shared_attributes
.display_window
.size;
(size.width() as u32, size.height() as u32)
}
fn color_type(&self) -> ColorType {
let returns_alpha = self.alpha_preference.unwrap_or(self.alpha_present_in_file);
if returns_alpha {
ColorType::Rgba32F
} else {
ColorType::Rgb32F
}
}
fn original_color_type(&self) -> ExtendedColorType {
if self.alpha_present_in_file {
ExtendedColorType::Rgba32F
} else {
ExtendedColorType::Rgb32F
}
}
/// Use `read_image` instead if possible,
/// as this method creates a whole new buffer just to contain the entire image.
fn into_reader(self) -> ImageResult<Self::Reader> {
Ok(Cursor::new(decoder_to_vec(self)?))
}
fn scanline_bytes(&self) -> u64 {
// we cannot always read individual scan lines for every file,
// as the tiles or lines in the file could be in random or reversed order.
// therefore we currently read all lines at once
// Todo: optimize for specific exr.line_order?
self.total_bytes()
}
// reads with or without alpha, depending on `self.alpha_preference` and `self.alpha_present_in_file`
fn read_image_with_progress<F: Fn(Progress)>(
self,
unaligned_bytes: &mut [u8],
progress_callback: F,
) -> ImageResult<()> {
let blocks_in_header = self.selected_exr_header().chunk_count as u64;
let channel_count = self.color_type().channel_count() as usize;
let display_window = self.selected_exr_header().shared_attributes.display_window;
let data_window_offset =
self.selected_exr_header().own_attributes.layer_position - display_window.position;
{
// check whether the buffer is large enough for the dimensions of the file
let (width, height) = self.dimensions();
let bytes_per_pixel = self.color_type().bytes_per_pixel() as usize;
let expected_byte_count = (width as usize)
.checked_mul(height as usize)
.and_then(|size| size.checked_mul(bytes_per_pixel));
// if the width and height does not match the length of the bytes, the arguments are invalid
let has_invalid_size_or_overflowed = expected_byte_count
.map(|expected_byte_count| unaligned_bytes.len() != expected_byte_count)
// otherwise, size calculation overflowed, is bigger than memory,
// therefore data is too small, so it is invalid.
.unwrap_or(true);
if has_invalid_size_or_overflowed {
panic!("byte buffer not large enough for the specified dimensions and f32 pixels");
}
}
let result = read()
.no_deep_data()
.largest_resolution_level()
.rgba_channels(
move |_size, _channels| vec![0_f32; display_window.size.area() * channel_count],
move |buffer, index_in_data_window, (r, g, b, a_or_1): (f32, f32, f32, f32)| {
let index_in_display_window =
index_in_data_window.to_i32() + data_window_offset;
// only keep pixels inside the data window
// TODO filter chunks based on this
if index_in_display_window.x() >= 0
&& index_in_display_window.y() >= 0
&& index_in_display_window.x() < display_window.size.width() as i32
&& index_in_display_window.y() < display_window.size.height() as i32
{
let index_in_display_window =
index_in_display_window.to_usize("index bug").unwrap();
let first_f32_index =
index_in_display_window.flat_index_for_size(display_window.size);
buffer[first_f32_index * channel_count
..(first_f32_index + 1) * channel_count]
.copy_from_slice(&[r, g, b, a_or_1][0..channel_count]);
// TODO white point chromaticities + srgb/linear conversion?
}
},
)
.first_valid_layer() // TODO select exact layer by self.header_index?
.all_attributes()
.on_progress(|progress| {
progress_callback(
Progress::new(
(progress * blocks_in_header as f64) as u64,
blocks_in_header,
), // TODO precision errors?
);
})
.from_chunks(self.exr_reader)
.map_err(to_image_err)?;
// TODO this copy is strictly not necessary, but the exr api is a little too simple for reading into a borrowed target slice
// this cast is safe and works with any alignment, as bytes are copied, and not f32 values.
// note: buffer slice length is checked in the beginning of this function and will be correct at this point
unaligned_bytes.copy_from_slice(bytemuck::cast_slice(
result.layer_data.channel_data.pixels.as_slice(),
));
Ok(())
}
}
/// Write a raw byte buffer of pixels,
/// returning an Error if it has an invalid length.
///
/// Assumes the writer is buffered. In most cases,
/// you should wrap your writer in a `BufWriter` for best performance.
// private. access via `OpenExrEncoder`
fn write_buffer(
mut buffered_write: impl Write + Seek,
unaligned_bytes: &[u8],
width: u32,
height: u32,
color_type: ColorType,
) -> ImageResult<()> {
let width = width as usize;
let height = height as usize;
{
// check whether the buffer is large enough for the specified dimensions
let expected_byte_count = width
.checked_mul(height)
.and_then(|size| size.checked_mul(color_type.bytes_per_pixel() as usize));
// if the width and height does not match the length of the bytes, the arguments are invalid
let has_invalid_size_or_overflowed = expected_byte_count
.map(|expected_byte_count| unaligned_bytes.len() < expected_byte_count)
// otherwise, size calculation overflowed, is bigger than memory,
// therefore data is too small, so it is invalid.
.unwrap_or(true);
if has_invalid_size_or_overflowed {
return Err(ImageError::Encoding(EncodingError::new(
ImageFormatHint::Exact(ImageFormat::OpenExr),
"byte buffer not large enough for the specified dimensions and f32 pixels",
)));
}
}
// bytes might be unaligned so we cannot cast the whole thing, instead lookup each f32 individually
let lookup_f32 = move |f32_index: usize| {
let unaligned_f32_bytes_slice = &unaligned_bytes[f32_index * 4..(f32_index + 1) * 4];
let f32_bytes_array = unaligned_f32_bytes_slice
.try_into()
.expect("indexing error");
f32::from_ne_bytes(f32_bytes_array)
};
match color_type {
ColorType::Rgb32F => {
exr::prelude::Image // TODO compression method zip??
::from_channels(
(width, height),
SpecificChannels::rgb(|pixel: Vec2<usize>| {
let pixel_index = 3 * pixel.flat_index_for_size(Vec2(width, height));
(
lookup_f32(pixel_index),
lookup_f32(pixel_index + 1),
lookup_f32(pixel_index + 2),
)
}),
)
.write()
// .on_progress(|progress| todo!())
.to_buffered(&mut buffered_write)
.map_err(to_image_err)?;
}
ColorType::Rgba32F => {
exr::prelude::Image // TODO compression method zip??
::from_channels(
(width, height),
SpecificChannels::rgba(|pixel: Vec2<usize>| {
let pixel_index = 4 * pixel.flat_index_for_size(Vec2(width, height));
(
lookup_f32(pixel_index),
lookup_f32(pixel_index + 1),
lookup_f32(pixel_index + 2),
lookup_f32(pixel_index + 3),
)
}),
)
.write()
// .on_progress(|progress| todo!())
.to_buffered(&mut buffered_write)
.map_err(to_image_err)?;
}
// TODO other color types and channel types
unsupported_color_type => {
return Err(ImageError::Encoding(EncodingError::new(
ImageFormatHint::Exact(ImageFormat::OpenExr),
format!(
"writing color type {:?} not yet supported",
unsupported_color_type
),
)))
}
}
Ok(())
}
// TODO is this struct and trait actually used anywhere?
/// A thin wrapper that implements `ImageEncoder` for OpenEXR images. Will behave like `image::codecs::openexr::write_buffer`.
#[derive(Debug)]
pub struct OpenExrEncoder<W>(W);
impl<W> OpenExrEncoder<W> {
/// Create an `ImageEncoder`. Does not write anything yet. Writing later will behave like `image::codecs::openexr::write_buffer`.
// use constructor, not public field, for future backwards-compatibility
pub fn new(write: W) -> Self {
Self(write)
}
}
impl<W> ImageEncoder for OpenExrEncoder<W>
where
W: Write + Seek,
{
/// Writes the complete image.
///
/// Returns an Error if it has an invalid length.
/// Assumes the writer is buffered. In most cases,
/// you should wrap your writer in a `BufWriter` for best performance.
fn write_image(
self,
buf: &[u8],
width: u32,
height: u32,
color_type: ColorType,
) -> ImageResult<()> {
write_buffer(self.0, buf, width, height, color_type)
}
}
fn to_image_err(exr_error: Error) -> ImageError {
ImageError::Decoding(DecodingError::new(
ImageFormatHint::Exact(ImageFormat::OpenExr),
exr_error.to_string(),
))
}
#[cfg(test)]
mod test {
use super::*;
use std::io::BufReader;
use std::path::{Path, PathBuf};
use crate::buffer_::{Rgb32FImage, Rgba32FImage};
use crate::error::{LimitError, LimitErrorKind};
use crate::{ImageBuffer, Rgb, Rgba};
const BASE_PATH: &[&str] = &[".", "tests", "images", "exr"];
/// Write an `Rgb32FImage`.
/// Assumes the writer is buffered. In most cases,
/// you should wrap your writer in a `BufWriter` for best performance.
fn write_rgb_image(write: impl Write + Seek, image: &Rgb32FImage) -> ImageResult<()> {
write_buffer(
write,
bytemuck::cast_slice(image.as_raw().as_slice()),
image.width(),
image.height(),
ColorType::Rgb32F,
)
}
/// Write an `Rgba32FImage`.
/// Assumes the writer is buffered. In most cases,
/// you should wrap your writer in a `BufWriter` for best performance.
fn write_rgba_image(write: impl Write + Seek, image: &Rgba32FImage) -> ImageResult<()> {
write_buffer(
write,
bytemuck::cast_slice(image.as_raw().as_slice()),
image.width(),
image.height(),
ColorType::Rgba32F,
)
}
/// Read the file from the specified path into an `Rgba32FImage`.
fn read_as_rgba_image_from_file(path: impl AsRef<Path>) -> ImageResult<Rgba32FImage> {
read_as_rgba_image(BufReader::new(std::fs::File::open(path)?))
}
/// Read the file from the specified path into an `Rgb32FImage`.
fn read_as_rgb_image_from_file(path: impl AsRef<Path>) -> ImageResult<Rgb32FImage> {
read_as_rgb_image(BufReader::new(std::fs::File::open(path)?))
}
/// Read the file from the specified path into an `Rgb32FImage`.
fn read_as_rgb_image(read: impl Read + Seek) -> ImageResult<Rgb32FImage> {
let decoder = OpenExrDecoder::with_alpha_preference(read, Some(false))?;
let (width, height) = decoder.dimensions();
let buffer: Vec<f32> = decoder_to_vec(decoder)?;
ImageBuffer::from_raw(width, height, buffer)
// this should be the only reason for the "from raw" call to fail,
// even though such a large allocation would probably cause an error much earlier
.ok_or_else(|| {
ImageError::Limits(LimitError::from_kind(LimitErrorKind::InsufficientMemory))
})
}
/// Read the file from the specified path into an `Rgba32FImage`.
fn read_as_rgba_image(read: impl Read + Seek) -> ImageResult<Rgba32FImage> {
let decoder = OpenExrDecoder::with_alpha_preference(read, Some(true))?;
let (width, height) = decoder.dimensions();
let buffer: Vec<f32> = decoder_to_vec(decoder)?;
ImageBuffer::from_raw(width, height, buffer)
// this should be the only reason for the "from raw" call to fail,
// even though such a large allocation would probably cause an error much earlier
.ok_or_else(|| {
ImageError::Limits(LimitError::from_kind(LimitErrorKind::InsufficientMemory))
})
}
#[test]
fn compare_exr_hdr() {
if cfg!(not(feature = "hdr")) {
eprintln!("warning: to run all the openexr tests, activate the hdr feature flag");
}
#[cfg(feature = "hdr")]
{
let folder = BASE_PATH.iter().collect::<PathBuf>();
let reference_path = folder.clone().join("overexposed gradient.hdr");
let exr_path = folder
.clone()
.join("overexposed gradient - data window equals display window.exr");
let hdr: Vec<Rgb<f32>> = crate::codecs::hdr::HdrDecoder::new(std::io::BufReader::new(
std::fs::File::open(&reference_path).unwrap(),
))
.unwrap()
.read_image_hdr()
.unwrap();
let exr_pixels: Rgb32FImage = read_as_rgb_image_from_file(exr_path).unwrap();
assert_eq!(
exr_pixels.dimensions().0 * exr_pixels.dimensions().1,
hdr.len() as u32
);
for (expected, found) in hdr.iter().zip(exr_pixels.pixels()) {
for (expected, found) in expected.0.iter().zip(found.0.iter()) {
// the large tolerance seems to be caused by
// the RGBE u8x4 pixel quantization of the hdr image format
assert!(
(expected - found).abs() < 0.1,
"expected {}, found {}",
expected,
found
);
}
}
}
}
#[test]
fn roundtrip_rgba() {
let mut next_random = vec![1.0, 0.0, -1.0, -3.14, 27.0, 11.0, 31.0]
.into_iter()
.cycle();
let mut next_random = move || next_random.next().unwrap();
let generated_image: Rgba32FImage = ImageBuffer::from_fn(9, 31, |_x, _y| {
Rgba([next_random(), next_random(), next_random(), next_random()])
});
let mut bytes = vec![];
write_rgba_image(Cursor::new(&mut bytes), &generated_image).unwrap();
let decoded_image = read_as_rgba_image(Cursor::new(bytes)).unwrap();
debug_assert_eq!(generated_image, decoded_image);
}
#[test]
fn roundtrip_rgb() {
let mut next_random = vec![1.0, 0.0, -1.0, -3.14, 27.0, 11.0, 31.0]
.into_iter()
.cycle();
let mut next_random = move || next_random.next().unwrap();
let generated_image: Rgb32FImage = ImageBuffer::from_fn(9, 31, |_x, _y| {
Rgb([next_random(), next_random(), next_random()])
});
let mut bytes = vec![];
write_rgb_image(Cursor::new(&mut bytes), &generated_image).unwrap();
let decoded_image = read_as_rgb_image(Cursor::new(bytes)).unwrap();
debug_assert_eq!(generated_image, decoded_image);
}
#[test]
fn compare_rgba_rgb() {
let exr_path = BASE_PATH
.iter()
.collect::<PathBuf>()
.join("overexposed gradient - data window equals display window.exr");
let rgb: Rgb32FImage = read_as_rgb_image_from_file(&exr_path).unwrap();
let rgba: Rgba32FImage = read_as_rgba_image_from_file(&exr_path).unwrap();
assert_eq!(rgba.dimensions(), rgb.dimensions());
for (Rgb(rgb), Rgba(rgba)) in rgb.pixels().zip(rgba.pixels()) {
assert_eq!(rgb, &rgba[..3]);
}
}
#[test]
fn compare_cropped() {
// like in photoshop, exr images may have layers placed anywhere in a canvas.
// we don't want to load the pixels from the layer, but we want to load the pixels from the canvas.
// a layer might be smaller than the canvas, in that case the canvas should be transparent black
// where no layer was covering it. a layer might also be larger than the canvas,
// these pixels should be discarded.
//
// in this test we want to make sure that an
// auto-cropped image will be reproduced to the original.
let exr_path = BASE_PATH.iter().collect::<PathBuf>();
let original = exr_path.clone().join("cropping - uncropped original.exr");
let cropped = exr_path
.clone()
.join("cropping - data window differs display window.exr");
// smoke-check that the exr files are actually not the same
{
let original_exr = read_first_flat_layer_from_file(&original).unwrap();
let cropped_exr = read_first_flat_layer_from_file(&cropped).unwrap();
assert_eq!(
original_exr.attributes.display_window,
cropped_exr.attributes.display_window
);
assert_ne!(
original_exr.layer_data.attributes.layer_position,
cropped_exr.layer_data.attributes.layer_position
);
assert_ne!(original_exr.layer_data.size, cropped_exr.layer_data.size);
}
// check that they result in the same image
let original: Rgba32FImage = read_as_rgba_image_from_file(&original).unwrap();
let cropped: Rgba32FImage = read_as_rgba_image_from_file(&cropped).unwrap();
assert_eq!(original.dimensions(), cropped.dimensions());
// the following is not a simple assert_eq, as in case of an error,
// the whole image would be printed to the console, which takes forever
assert!(original.pixels().zip(cropped.pixels()).all(|(a, b)| a == b));
}
}