imagebmp is extremely slow on Windows

Description

imagebmp is extremely slow on Windows.

(PS, there is also a performance issue with imagegrabscreen(), it is much slower than equivalent Python-mss code: #23459 )

The following code:

<?php

$t = microtime(true);
$h = imagegrabscreen();
$grab = microtime(true) - $t;

echo 'Grab: ' . sprintf('%.9f', $grab) . " s\n";

$t = microtime(true);
$r = imagebmp($h, 'bmp0.bmp', false);
$dt = microtime(true) - $t;
echo 'BMP no compression: ' . sprintf('%.9f', $dt) . ' s (result: ' . var_export($r, true) . ')' . "\n";

$t = microtime(true);
$r = imagebmp($h, 'bmp1.bmp', true);
$dt = microtime(true) - $t;
echo 'BMP compressed: ' . sprintf('%.9f', $dt) . ' s (result: ' . var_export($r, true) . ')' . "\n";

$t = microtime(true);
$r = imagepng($h, 'png0.png', 0);
$dt = microtime(true) - $t;
echo 'PNG no compression: ' . sprintf('%.9f', $dt) . ' s (result: ' . var_export($r, true) . ')' . "\n";

$t = microtime(true);
$r = imagepng($h, 'pngd.png', -1);
$dt = microtime(true) - $t;
echo 'PNG default compression: ' . sprintf('%.9f', $dt) . ' s (result: ' . var_export($r, true) . ')' . "\n";

imagedestroy($h);

Resulted in this output:

PS C:\Users\hansh> php test.php
Grab: 7.558355093 s
BMP no compression: 48.639475107 s (result: true)
BMP compressed: 52.303011179 s (result: true)
PNG no compression: 0.094882011 s (result: true)
PNG default compression: 0.109680176 s (result: true)
PHP Deprecated:  Function imagedestroy() is deprecated since 8.5, as it has no effect since PHP 8.0 in C:\Users\hansh\test.php on line 29

Deprecated: Function imagedestroy() is deprecated since 8.5, as it has no effect since PHP 8.0 in C:\Users\hansh\test.php on line 29

But I expected this output instead:

BMP no compression: 0.019475107 s (result: true)
BMP compressed: 0.013011179 s (result: true)

png executed in 0.01 seconds, BMP needs 40 seconds.

PHP Version

Observed both windows 11 with
PHP 8.5.1 (cli) (built: Dec 17 2025 10:55:54) (ZTS Visual C++ 2022 x64)
Copyright (c) The PHP Group
Zend Engine v4.5.1, Copyright (c) Zend Technologies
    with Zend OPcache v8.5.1, Copyright (c), by Zend Technologies

and Windows Server 2025 with
PHP 8.2.12 (cli) (built: Oct 24 2023 21:15:15) (ZTS Visual C++ 2019 x64)
Copyright (c) The PHP Group
Zend Engine v4.2.12, Copyright (c) Zend Technologies

Operating System

Observed on both Windows Server 2025, and Windows 11, both x86-64

For comparsion, Python-mss +PIL does everything combined in <1s:

PS C:\Users\hansh> python3 test.py
Grab: 0.265929600 s
BMP no compression: 0.069192300 s (result: True)
BMP compressed (PIL ignores this): 0.022632100 s (result: True)
PNG no compression: 0.105889400 s (result: True)
PNG default compression: 0.093167300 s (result: True)

import time
import mss
from PIL import Image

# 1. Grab Screen
t = time.perf_counter()
with mss.MSS() as sct:  
    # monitors[1] is the primary monitor (monitors[0] is all monitors combined)
    monitor = sct.monitors[1] 
    sct_img = sct.grab(monitor)
    
    # Convert raw MSS pixels (BGRA) to a PIL Image (RGB)
    img = Image.frombytes("RGB", sct_img.size, sct_img.bgra, "raw", "BGRX")
    
grab_time = time.perf_counter() - t
print(f"Grab: {grab_time:.9f} s")

# 2. BMP no compression
t = time.perf_counter()
try:
    img.save('bmp0.bmp', format='BMP')
    r = True
except Exception:
    r = False
dt = time.perf_counter() - t
print(f"BMP no compression: {dt:.9f} s (result: {r})")

# 3. BMP compressed (PIL does not support writing compressed BMPs)
t = time.perf_counter()
try:
    img.save('bmp1.bmp', format='BMP')
    r = True
except Exception:
    r = False
dt = time.perf_counter() - t
print(f"BMP compressed (PIL ignores this): {dt:.9f} s (result: {r})")

# 4. PNG no compression (compress_level=0)
t = time.perf_counter()
try:
    img.save('png0.png', format='PNG', compress_level=0)
    r = True
except Exception:
    r = False
dt = time.perf_counter() - t
print(f"PNG no compression: {dt:.9f} s (result: {r})")

# 5. PNG default compression
t = time.perf_counter()
try:
    img.save('pngd.png', format='PNG') 
    r = True
except Exception:
    r = False
dt = time.perf_counter() - t
print(f"PNG default compression: {dt:.9f} s (result: {r})")

Fix phpGH-23457: imagebmp() is extremely slow when writing to a file

Merge branch 'PHP-8.4' into PHP-8.5

Merge branch 'PHP-8.5'

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imagebmp is extremely slow on Windows #23457

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imagebmp is extremely slow on Windows #23457

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divinity76 commented on Aug 25, 2026

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