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@codeflash-ai codeflash-ai bot commented Dec 17, 2025

📄 162% (1.62x) speedup for rgb_to_hsv in lib/matplotlib/colors.py

⏱️ Runtime : 94.8 milliseconds 36.2 milliseconds (best of 10 runs)

📝 Explanation and details

The optimized code achieves a 162% speedup by eliminating expensive operations and reducing memory allocations. The key optimizations are:

What was optimized:

  1. Replaced expensive np.ptp() with direct subtraction: The original used np.ptp(arr, -1) (30.6% of runtime), which internally computes both max and min. The optimized version computes arr_max - arr_min directly, reusing the already-computed min/max values.

  2. Used faster min/max functions: Replaced arr.max(-1) with np.maximum.reduce([r, g, b]) for the 3-channel case, which is more efficient for small fixed dimensions.

  3. Eliminated redundant indexing operations: The original performed expensive boolean array indexing three times (out[idx, 0] = ... taking 13.1-13.2% each). The optimized version precomputes all arithmetic using vectorized operations with out= parameters, then assigns results in bulk.

  4. Reduced memory allocations: Used np.empty_like() instead of np.zeros_like() where initialization isn't needed, and leveraged NumPy's out= parameter to reuse buffers and avoid temporary arrays.

Why it's faster:

  • Memory efficiency: Fewer allocations and better cache locality from reusing buffers
  • Vectorization: Bulk operations on entire arrays instead of masked subsets
  • Computational efficiency: Eliminates the expensive np.ptp() operation that was the single largest bottleneck

Impact on workloads:
The function is called from blend_hsv() for shaded relief visualization, processing image data arrays. The optimization particularly benefits large image processing workloads - test results show 77-88% speedups on large batches (1000+ colors) while maintaining similar performance on small inputs, making it ideal for the image processing context where this function is used.

Correctness verification report:

Test Status
⚙️ Existing Unit Tests 1445 Passed
🌀 Generated Regression Tests 27 Passed
⏪ Replay Tests 🔘 None Found
🔎 Concolic Coverage Tests 🔘 None Found
📊 Tests Coverage 100.0%
⚙️ Existing Unit Tests and Runtime
Test File::Test Function Original ⏱️ Optimized ⏱️ Speedup
test_colors.py::test_rgb_hsv_round_trip 92.1ms 34.1ms 170%✅
🌀 Generated Regression Tests and Runtime
import numpy as np

# imports
import pytest  # used for our unit tests
from matplotlib.colors import rgb_to_hsv

# --------------------- Basic Test Cases ---------------------


def test_invalid_shape_last_dim_not_3():
    # Input shape (..., 2) should raise ValueError
    rgb = [1, 0]
    with pytest.raises(ValueError):
        rgb_to_hsv(rgb)  # 9.48μs -> 9.49μs (0.084% slower)


def test_invalid_shape_high_dim():
    # Input shape (..., 4) should raise ValueError
    rgb = [[1, 0, 0, 0]]
    with pytest.raises(ValueError):
        rgb_to_hsv(rgb)  # 9.85μs -> 9.82μs (0.224% faster)


def test_empty_input():
    # Empty input with shape (0, 3) should return empty output
    rgb = np.empty((0, 3))
    codeflash_output = rgb_to_hsv(rgb)
    result = codeflash_output  # 75.8μs -> 71.4μs (6.06% faster)


def test_input_with_nan():
    # Input with NaN should propagate NaN in output
    rgb = [np.nan, 0, 1]
    codeflash_output = rgb_to_hsv(rgb)
    result = codeflash_output  # 80.9μs -> 80.5μs (0.486% faster)


def test_input_with_negative_values():
    # Negative values are allowed by numpy but not in [0,1] range; function does not check, so it should compute
    rgb = [-0.5, 0.5, 0.5]
    # The output should be deterministic and not crash
    codeflash_output = rgb_to_hsv(rgb)
    result = codeflash_output  # 89.8μs -> 84.6μs (6.17% faster)


def test_input_with_values_above_one():
    # Values above 1 are not checked; should compute without error
    rgb = [1.5, 1, 0.5]
    codeflash_output = rgb_to_hsv(rgb)
    result = codeflash_output  # 82.0μs -> 78.8μs (4.10% faster)


def test_input_1d_array():
    # 1D array input should be accepted
    rgb = np.array([0.2, 0.4, 0.6])
    codeflash_output = rgb_to_hsv(rgb)
    result = codeflash_output  # 82.1μs -> 78.2μs (5.09% faster)


def test_large_batch_of_colors():
    # Test with a large batch of random RGB colors
    np.random.seed(42)
    rgb = np.random.rand(1000, 3)
    codeflash_output = rgb_to_hsv(rgb)
    result = codeflash_output  # 248μs -> 140μs (76.6% faster)


def test_large_batch_performance():
    # Test that the function runs efficiently on a large batch
    rgb = np.random.rand(999, 3)
    codeflash_output = rgb_to_hsv(rgb)
    result = codeflash_output  # 246μs -> 141μs (74.1% faster)


def test_large_multidimensional_array():
    # Test with a large 3D array
    rgb = np.random.rand(10, 10, 10, 3)
    codeflash_output = rgb_to_hsv(rgb)
    result = codeflash_output  # 277μs -> 147μs (88.3% faster)


# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.
import numpy as np

# imports
import pytest  # used for our unit tests
from matplotlib.colors import rgb_to_hsv

# unit tests


# Helper to compare HSV values with tolerance for floating point errors
def assert_hsv_close(actual, expected, tol=1e-7):
    actual = np.asarray(actual)
    expected = np.asarray(expected)


# ---------------------------
# 1. BASIC TEST CASES
# ---------------------------


def test_shape_error():
    # Input with wrong shape (not (...,3)), should raise ValueError
    with pytest.raises(ValueError):
        rgb_to_hsv([1, 0])  # 8.60μs -> 8.57μs (0.315% faster)

    with pytest.raises(ValueError):
        rgb_to_hsv(
            [[1, 0, 0], [0, 1, 0], [0, 0, 1], [1, 1, 1, 0]]
        )  # 3.59μs -> 3.90μs (7.96% slower)


def test_1d_input():
    # Accepts 1D input of length 3
    codeflash_output = rgb_to_hsv([0.1, 0.2, 0.3])
    result = codeflash_output  # 87.1μs -> 82.3μs (5.83% faster)
    # max=0.3, min=0.1, delta=0.2, V=0.3, S=0.2/0.3=0.666...
    # B is max, H = 4 + (0.1-0.2)/0.2 = 4 - 0.5 = 3.5/6 = 0.583333...
    expected = [0.5833333333333334, 2 / 3, 0.3]
    assert_hsv_close(result, expected)


def test_dtype_int():
    # Accepts integer input, but converts to float
    arr = np.array([255, 0, 0])
    arr = arr / 255.0
    codeflash_output = rgb_to_hsv(arr)
    result = codeflash_output  # 74.7μs -> 69.7μs (7.17% faster)
    assert_hsv_close(result, [0, 1, 1])


def test_dtype_uint8():
    # Accepts uint8 input, but converts to float
    arr = np.array([255, 255, 0], dtype=np.uint8)
    arr = arr / 255.0
    codeflash_output = rgb_to_hsv(arr)
    result = codeflash_output  # 73.7μs -> 69.3μs (6.30% faster)
    assert_hsv_close(result, [1 / 6, 1, 1])


def test_zero_saturation():
    # Test for color with zero saturation (gray)
    arr = [0.4, 0.4, 0.4]
    codeflash_output = rgb_to_hsv(arr)
    result = codeflash_output  # 78.0μs -> 74.8μs (4.23% faster)
    # H is undefined, but should be 0, S=0, V=0.4
    assert_hsv_close(result, [0, 0, 0.4])


def test_near_zero_delta():
    # Test for color with very small delta
    arr = [0.500001, 0.5, 0.5]
    codeflash_output = rgb_to_hsv(arr)
    result = codeflash_output  # 80.4μs -> 77.1μs (4.33% faster)
    # Should be very close to gray, H=0, S ~0.000002/0.500001, V=0.500001
    expected = [0, (0.500001 - 0.5) / 0.500001, 0.500001]
    assert_hsv_close(result, expected)


def test_negative_values():
    # Negative values should not be clipped, but will produce out-of-range HSV
    arr = [-0.1, 0.2, 0.3]
    # max=0.3, min=-0.1, delta=0.4, V=0.3, S=0.4/0.3=1.333...
    # B is max, H = 4 + (-0.1-0.2)/0.4 = 4 - 0.75 = 3.25/6 = 0.541666...
    expected = [0.5416666666666666, 1.3333333333333333, 0.3]
    codeflash_output = rgb_to_hsv(arr)
    result = codeflash_output  # 81.2μs -> 76.7μs (5.89% faster)
    assert_hsv_close(result, expected)


def test_above_one_values():
    # Values above 1 should not be clipped, but will produce V>1
    arr = [1.2, 0.6, 0.6]
    # max=1.2, min=0.6, delta=0.6, V=1.2, S=0.6/1.2=0.5
    # R is max, H=(0.6-0.6)/0.6=0, H=0/6=0
    expected = [0, 0.5, 1.2]
    codeflash_output = rgb_to_hsv(arr)
    result = codeflash_output  # 79.8μs -> 75.4μs (5.85% faster)
    assert_hsv_close(result, expected)


def test_input_with_nan():
    # Test input with NaN
    arr = [np.nan, 0.5, 0.5]
    codeflash_output = rgb_to_hsv(arr)
    result = codeflash_output  # 82.5μs -> 79.9μs (3.36% faster)


def test_preserve_shape_nd():
    # Test that shape is preserved for nD input
    arr = np.ones((2, 3, 3))
    codeflash_output = rgb_to_hsv(arr)
    result = codeflash_output  # 83.8μs -> 77.1μs (8.76% faster)


def test_empty_input():
    # Empty input with shape (0,3) should return empty output
    arr = np.empty((0, 3))
    codeflash_output = rgb_to_hsv(arr)
    result = codeflash_output  # 68.9μs -> 65.2μs (5.78% faster)


# ---------------------------
# 3. LARGE SCALE TEST CASES
# ---------------------------


def test_large_batch():
    # Test with a large batch of colors (1000,3)
    arr = np.random.rand(1000, 3)
    codeflash_output = rgb_to_hsv(arr)
    result = codeflash_output  # 242μs -> 137μs (77.0% faster)


def test_large_nd_batch():
    # Test with a large nD batch (10, 10, 10, 3)
    arr = np.random.rand(10, 10, 10, 3)
    codeflash_output = rgb_to_hsv(arr)
    result = codeflash_output  # 273μs -> 146μs (86.6% faster)


def test_performance_large_batch(benchmark):
    # Benchmark performance on a large batch
    arr = np.random.rand(1000, 3)
    benchmark(rgb_to_hsv, arr)


# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.

To edit these changes git checkout codeflash/optimize-rgb_to_hsv-mja51eyp and push.

Codeflash Static Badge

The optimized code achieves a **162% speedup** by eliminating expensive operations and reducing memory allocations. The key optimizations are:

**What was optimized:**
1. **Replaced expensive `np.ptp()` with direct subtraction**: The original used `np.ptp(arr, -1)` (30.6% of runtime), which internally computes both max and min. The optimized version computes `arr_max - arr_min` directly, reusing the already-computed min/max values.

2. **Used faster min/max functions**: Replaced `arr.max(-1)` with `np.maximum.reduce([r, g, b])` for the 3-channel case, which is more efficient for small fixed dimensions.

3. **Eliminated redundant indexing operations**: The original performed expensive boolean array indexing three times (`out[idx, 0] = ...` taking 13.1-13.2% each). The optimized version precomputes all arithmetic using vectorized operations with `out=` parameters, then assigns results in bulk.

4. **Reduced memory allocations**: Used `np.empty_like()` instead of `np.zeros_like()` where initialization isn't needed, and leveraged NumPy's `out=` parameter to reuse buffers and avoid temporary arrays.

**Why it's faster:**
- **Memory efficiency**: Fewer allocations and better cache locality from reusing buffers
- **Vectorization**: Bulk operations on entire arrays instead of masked subsets
- **Computational efficiency**: Eliminates the expensive `np.ptp()` operation that was the single largest bottleneck

**Impact on workloads:**
The function is called from `blend_hsv()` for shaded relief visualization, processing image data arrays. The optimization particularly benefits large image processing workloads - test results show 77-88% speedups on large batches (1000+ colors) while maintaining similar performance on small inputs, making it ideal for the image processing context where this function is used.
@codeflash-ai codeflash-ai bot requested a review from mashraf-222 December 17, 2025 15:00
@codeflash-ai codeflash-ai bot added ⚡️ codeflash Optimization PR opened by Codeflash AI 🎯 Quality: High Optimization Quality according to Codeflash labels Dec 17, 2025
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⚡️ codeflash Optimization PR opened by Codeflash AI 🎯 Quality: High Optimization Quality according to Codeflash

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