diff --git a/Tests/test_imageops.py b/Tests/test_imageops.py index 33489bd13..93be34bf8 100644 --- a/Tests/test_imageops.py +++ b/Tests/test_imageops.py @@ -29,6 +29,7 @@ def test_sanity(): ImageOps.autocontrast(hopper("L"), cutoff=(2, 10)) ImageOps.autocontrast(hopper("L"), ignore=[0, 255]) ImageOps.autocontrast(hopper("L"), mask=hopper("L")) + ImageOps.autocontrast(hopper("L"), preserve_tone=True) ImageOps.colorize(hopper("L"), (0, 0, 0), (255, 255, 255)) ImageOps.colorize(hopper("L"), "black", "white") @@ -336,7 +337,7 @@ def test_autocontrast_mask_toy_input(): assert ImageStat.Stat(result_nomask).median == [128] -def test_auto_contrast_mask_real_input(): +def test_autocontrast_mask_real_input(): # Test the autocontrast with a rectangular mask with Image.open("Tests/images/iptc.jpg") as img: @@ -362,3 +363,52 @@ def test_auto_contrast_mask_real_input(): threshold=2, msg="autocontrast without mask pixel incorrect", ) + + +def test_autocontrast_preserve_tone(): + def autocontrast(mode, preserve_tone): + im = hopper(mode) + return ImageOps.autocontrast(im, preserve_tone=preserve_tone).histogram() + + assert autocontrast("RGB", True) != autocontrast("RGB", False) + assert autocontrast("L", True) == autocontrast("L", False) + + +def test_autocontrast_preserve_gradient(): + gradient = Image.linear_gradient("L") + + # test with a grayscale gradient that extends to 0,255. + # Should be a noop. + out = ImageOps.autocontrast(gradient, cutoff=0, preserve_tone=True) + + assert_image_equal(gradient, out) + + # cutoff the top and bottom + # autocontrast should make the first and last histogram entries equal + # and, with rounding, should be 10% of the image pixels + out = ImageOps.autocontrast(gradient, cutoff=10, preserve_tone=True) + hist = out.histogram() + assert hist[0] == hist[-1] + assert hist[-1] == 256 * round(256 * 0.10) + + # in rgb + img = gradient.convert("RGB") + out = ImageOps.autocontrast(img, cutoff=0, preserve_tone=True) + assert_image_equal(img, out) + + +@pytest.mark.parametrize( + "color", ((255, 255, 255), (127, 255, 0), (127, 127, 127), (0, 0, 0)) +) +def test_autocontrast_preserve_one_color(color): + img = Image.new("RGB", (10, 10), color) + + # single color images shouldn't change + out = ImageOps.autocontrast(img, cutoff=0, preserve_tone=True) + assert_image_equal(img, out) # single color, no cutoff + + # even if there is a cutoff + out = ImageOps.autocontrast( + img, cutoff=10, preserve_tone=True + ) # single color 10 cutoff + assert_image_equal(img, out) diff --git a/docs/releasenotes/8.2.0.rst b/docs/releasenotes/8.2.0.rst index 3ef05894d..434d2eba9 100644 --- a/docs/releasenotes/8.2.0.rst +++ b/docs/releasenotes/8.2.0.rst @@ -83,6 +83,15 @@ be specified through a keyword argument:: im.save("out.tif", icc_profile=...) + +ImageOps.autocontrast: preserve_tone +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The default behaviour of :py:meth:`~PIL.ImageOps.autocontrast` is to normalize +separate histograms for each color channel, changing the tone of the image. The new +``preserve_tone`` argument keeps the tone unchanged by using one luminance histogram +for all channels. + Security ======== diff --git a/src/PIL/ImageOps.py b/src/PIL/ImageOps.py index 14602a5c8..d69a304ca 100644 --- a/src/PIL/ImageOps.py +++ b/src/PIL/ImageOps.py @@ -61,7 +61,7 @@ def _lut(image, lut): # actions -def autocontrast(image, cutoff=0, ignore=None, mask=None): +def autocontrast(image, cutoff=0, ignore=None, mask=None, preserve_tone=False): """ Maximize (normalize) image contrast. This function calculates a histogram of the input image (or mask region), removes ``cutoff`` percent of the @@ -77,9 +77,17 @@ def autocontrast(image, cutoff=0, ignore=None, mask=None): :param mask: Histogram used in contrast operation is computed using pixels within the mask. If no mask is given the entire image is used for histogram computation. + :param preserve_tone: Preserve image tone in Photoshop-like style autocontrast. + + .. versionadded:: 8.2.0 + :return: An image. """ - histogram = image.histogram(mask) + if preserve_tone: + histogram = image.convert("L").histogram(mask) + else: + histogram = image.histogram(mask) + lut = [] for layer in range(0, len(histogram), 256): h = histogram[layer : layer + 256]