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Improve imageops

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Fix issues and add better tests. Require hypothesis.
This commit is contained in:
James R. Barlow
2023-04-15 17:48:33 -07:00
parent 10f4c48e0b
commit 2b30f74fce
4 changed files with 92 additions and 32 deletions
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.gitignore
+1
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@@ -6,6 +6,7 @@
.venv*/
.tox/
.vscode/
.hypothesis/
.ipynb_checkpoints/
.mypy_cache/
.pytest_cache/
pyproject.toml
+1
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@@ -69,6 +69,7 @@ docs = ["sphinx", "sphinx-issues", "sphinx-rtd-theme"]
extended_test = ["PyMuPDF==1.19.1"]
test = [
"coverage[toml]>=5",
"hypothesis>=6.0.0",
"pytest>=6.0.0",
"pytest-cov>=2.11.1",
"pytest-xdist>=2.2.0",
src/ocrmypdf/imageops.py
+68 -32
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@@ -6,7 +6,8 @@
from __future__ import annotations
import logging
from math import ceil, floor, sqrt
from functools import singledispatch
from math import floor, sqrt
from PIL import Image
@@ -26,14 +27,71 @@ def bytes_per_pixel(mode: str) -> int:
return 4
@singledispatch
def calculate_downsample(
image: Image.Image,
image_size: tuple[int, int],
bytes_per_pixel: int,
*,
max_size: tuple[int, int] | None = None,
max_pixels: int | None = None,
max_bytes: int | None = None,
) -> tuple[int, int]:
"""Calculate image size required to downsample an image to fit lmiits.
"""Calculate image size required to downsample an image to fit limits.
If no limit is exceeded, the input image's size is returned.
Args:
image_size: Dimensions of image.
bytes_per_pixel: Number of bytes per pixel.
max_size: The maximum width and height of the image.
max_pixels: The maximum number of pixels in the image. Some image consumers
limit the total number of pixels as some value other than width*height.
max_bytes: The maximum number of bytes in the image. RGB is counted as 4
bytes; all other modes are counted as 1 byte.
"""
size = image_size
if max_size is not None:
overage = max_size[0] / size[0], max_size[1] / size[1]
size_factor = min(overage)
if size_factor < 1.0:
log.debug("Resizing image to fit Tesseract image size limit")
size = (
max(floor(size[0] * size_factor), 1),
max(floor(size[1] * size_factor), 1),
)
if max_pixels is not None:
if size[0] * size[1] > max_pixels:
log.debug("Resizing image to fit image pixel limit")
pixels_factor = sqrt(max_pixels / (size[0] * size[1]))
size = floor(size[0] * pixels_factor), floor(size[1] * pixels_factor)
if max_bytes is not None:
bpp = bytes_per_pixel
# stride = bytes per line
stride = size[0] * bpp
height = size[1]
if stride * height > max_bytes:
log.debug("Resizing image to fit image byte size limit")
bytes_factor = sqrt(max_bytes / (stride * height))
scaled_stride = max(floor(stride * bytes_factor), 1)
scaled_height = max(floor(height * bytes_factor), 1)
size = floor(scaled_stride / bpp), scaled_height
return size
@calculate_downsample.register
def _(
image: Image.Image,
arg: None = None,
*,
max_size: tuple[int, int] | None = None,
max_pixels: int | None = None,
max_bytes: int | None = None,
) -> tuple[int, int]:
"""Calculate image size required to downsample an image to fit limits.
If no limit is exceeded, the input image's size is returned.
@@ -45,35 +103,13 @@ def calculate_downsample(
max_bytes: The maximum number of bytes in the image. RGB is counted as 4
bytes; all other modes are counted as 1 byte.
"""
size = image.size
if max_size is not None:
major_axis = max(image.size)
size_factor = max(max_size) / major_axis
if size_factor < 1.0:
log.debug("Resizing image to fit Tesseract image size limit")
size = floor(size[0] * size_factor), floor(size[1] * size_factor)
if max_pixels is not None:
if size[0] * size[1] > max_pixels:
log.debug("Resizing image to fit image pixel limit")
pixels_factor = sqrt(max_pixels / (image.size[0] * image.size[1]))
size = floor(size[0] * pixels_factor), floor(size[1] * pixels_factor)
if max_bytes is not None:
bpp = bytes_per_pixel(image.mode)
# stride = bytes per line
stride = size[0] * bpp
height = size[1]
if stride * height > max_bytes:
log.debug("Resizing image to fit image byte size limit")
bytes_factor = sqrt((max_bytes) / (stride * height))
scaled_stride = floor(stride * bytes_factor)
scaled_height = floor(height * bytes_factor)
size = ceil(scaled_stride / bpp), scaled_height
assert (size[0] * bpp * size[1]) <= max_bytes
return size
return calculate_downsample(
image.size,
bytes_per_pixel(image.mode),
max_size=max_size,
max_pixels=max_pixels,
max_bytes=max_bytes,
)
def downsample_image(
tests/test_imageops.py
+22
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@@ -3,6 +3,8 @@
from __future__ import annotations
import hypothesis.strategies as st
from hypothesis import given
from PIL import Image
from ocrmypdf.imageops import bytes_per_pixel, calculate_downsample, downsample_image
@@ -23,6 +25,26 @@ def test_calculate_downsample():
assert calculate_downsample(im, max_bytes=100000) == (100, 100)
@given(
st.one_of(st.just("RGB"), st.just('L')),
st.integers(min_value=1, max_value=100000),
st.integers(min_value=1, max_value=100000),
st.integers(min_value=64, max_value=100000),
st.integers(min_value=64, max_value=100000),
st.integers(min_value=64 * 64, max_value=1000000),
)
def test_calculate_downsample_hypothesis(mode, im_w, im_h, max_x, max_y, max_bytes):
result = calculate_downsample(
(im_w, im_h),
bytes_per_pixel(mode),
max_size=(max_x, max_y),
max_bytes=max_bytes,
)
assert result[0] <= max_x
assert result[1] <= max_y
assert result[0] * result[1] * bytes_per_pixel(mode) <= max_bytes
def test_downsample_image():
im = Image.new('RGB', (100, 100))
im.info['dpi'] = (300, 300)