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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchSet the browser window size explicitly with driver.set_window_size(width, height), then check the page’s actual CSS viewport before taking the screenshot. The requested browser-window size, the page viewport and the saved image’s pixel dimensions are separate measurements, so verify the one your test or output actually depends on.
Set the window size before loading the page
For a repeatable Selenium screenshot, choose dimensions, apply them to the browser window, inspect the resulting dimensions, and then navigate to the page. Setting the size before navigation matters when the site’s responsive layout should load at your target width.
This example uses Chrome and a target browser-window size of 1280 × 900 pixels. Those numbers are an example, not a guarantee that the page viewport or PNG will have the same dimensions.
from selenium import webdriver
TARGET_WIDTH = 1280
TARGET_HEIGHT = 900
URL = "https://example.com"
options = webdriver.ChromeOptions()
# For headless runs, use the headless syntax supported by your installed Chrome version.
# For example, add the appropriate options.add_argument(...) here.
driver = webdriver.Chrome(options=options)
try:
driver.set_window_size(TARGET_WIDTH, TARGET_HEIGHT)
# These are browser-window dimensions reported by WebDriver.
print("WebDriver window:", driver.get_window_size())
print("WebDriver window rectangle:", driver.get_window_rect())
# These are the page's CSS viewport dimensions.
viewport = driver.execute_script(
"return {width: window.innerWidth, height: window.innerHeight}"
)
print("CSS viewport:", viewport)
driver.get(URL)
driver.save_screenshot("screenshot.png")
finally:
driver.quit()The Selenium Python Chromium WebDriver API documents set_window_size(width, height) in pixels, along with get_window_size() and get_window_rect() for inspecting the result. Selenium’s window guide also demonstrates setting a window size in Python. These are WebDriver window controls; they do not establish the CSS viewport size by themselves. Selenium Python Chromium WebDriver API · Selenium: Working with windows and tabs
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- Decide which dimensions matter to your use case: a browser-window size, the page’s CSS viewport, or the final image’s pixel dimensions.
- Start the intended browser and mode. If running headless, use syntax supported by the installed browser version rather than assuming all Chrome versions accept the same option.
- Call
driver.set_window_size(width, height)before navigating when the page should render at the target responsive width. - Inspect
driver.get_window_size()ordriver.get_window_rect(), then readwindow.innerWidthandwindow.innerHeightif the page layout depends on its CSS viewport. - Navigate, wait for the page state and visual assets your capture requires, and save the screenshot.
- If exact PNG dimensions matter, inspect the resulting file in the same environment that will run the capture.
Know which dimensions Selenium is reporting
“Window size” can refer to different things in a screenshot workflow. A reliable test records the relevant measurements separately instead of assuming a size request controls every layer.
| Measurement or control | What it tells or controls | Important qualification |
|---|---|---|
set_window_size(width, height) |
Requests the browser window’s width and height in pixels. | Check the resulting values with get_window_size() or get_window_rect(). |
window.innerWidth and window.innerHeight |
The CSS viewport dimensions reported to page JavaScript; these are useful for checking responsive breakpoints. | A requested outer browser-window size does not prove that the CSS viewport matches it. |
save_screenshot(path) |
Saves a PNG screenshot of the current top-level browsing context. | The WebDriver standard defines screenshot capture in terms of the visual viewport. Verify the image itself if its exact pixel dimensions matter. |
| PNG pixel dimensions | The width and height of the saved image file. | Do not infer them from the requested window dimensions; inspect the generated PNG in the target environment. |
The Selenium Python Remote WebDriver API documents save_screenshot() and get_screenshot_as_file() for saving PNG files, and get_screenshot_as_png() for retrieving PNG bytes. The WebDriver standard describes screenshots as captures of the visual viewport of the top-level browsing context. Selenium Python Remote WebDriver API · W3C WebDriver specification
Validate the saved PNG when file dimensions matter
If another system requires a particular image size, check the PNG rather than relying on a window-size request. A PNG file stores its dimensions near the start of the file; this small standard-library check reads them after Selenium saves the screenshot.
import struct
with open("screenshot.png", "rb") as image_file:
header = image_file.read(24)
if len(header) < 24 or header[:8] != b"x89PNGrnx1an":
raise ValueError("The output is not a valid PNG file")
pixel_width, pixel_height = struct.unpack(">II", header[16:24])
print(f"PNG dimensions: {pixel_width} × {pixel_height} pixels")This validation reports the file’s pixel dimensions; it does not change the browser viewport or make two captures visually identical. If the output size differs from what your pipeline expects, adjust the browser or emulation setup for the target environment and verify the generated file again.
Make repeated captures more comparable
A fixed window size removes one source of variation, but it is not a bit-for-bit reproducibility guarantee across machines. Browser chrome, the operating-system window manager, headless implementation, device scale, fonts and browser version can affect rendered output. For repeatable runs, record the browser and driver versions, operating system or container, headed/headless mode, requested window dimensions, measured viewport, and any device-scale or emulation settings.
Rank #2
- Set dimensions explicitly. Do not rely on the desktop’s current resolution or a maximize operation when the test needs a defined size.
- Measure after setting. Log WebDriver’s reported window values and the CSS viewport values relevant to the page.
- Navigate at the intended width. Responsive pages may choose layout based on the viewport available during loading.
- Control page readiness for your site. A screenshot taken before required content, fonts or images appear can differ even when the viewport is unchanged. Wait for the condition your application needs before capture.
- Validate the artifact. Inspect the PNG dimensions—and, when visual equality matters, compare the actual images in the same runtime environment.
The API documentation establishes the size and screenshot methods, but it does not promise that a requested outer window size will always equal either the CSS viewport or final PNG pixel dimensions. Nor do the cited sources establish a cross-browser recipe that guarantees identical rendered pixels on different hosts.
Use Chromium emulation only when you need viewport-level control
For Chromium-only workflows that need direct device metrics or viewport emulation, Chrome DevTools Protocol (CDP) offers Emulation.setDeviceMetricsOverride. Its parameters include width, height, mobile emulation and device scale factor; the protocol reference says the command overrides values including window.innerWidth, window.innerHeight and related CSS media-query results.
CDP is a browser-specific option, not a portable WebDriver command. Use it when that Chromium dependency is acceptable and ordinary window sizing does not provide the control you need. Chrome DevTools Protocol: Emulation domain
Troubleshoot inconsistent Selenium screenshots
The CSS viewport is smaller or larger than the requested window
Cause: WebDriver’s window dimensions and the page’s CSS viewport are different measurements; browser chrome and the environment may affect the usable area.
Fix: Print driver.get_window_size() and window.innerWidth/window.innerHeight separately. If the responsive layout is the concern, treat the JavaScript viewport measurement as the relevant check. For Chromium-specific viewport emulation, consider CDP and document that browser dependency.
Rank #3
The PNG is not the dimensions you requested
Cause: A window-size request alone does not guarantee matching screenshot pixel dimensions.
Fix: Read the PNG dimensions after capture and confirm the window, viewport, browser mode and device-scale settings in the target environment. Do not compensate by assuming a fixed conversion between the three measurements.
The page uses a different responsive layout between runs
Cause: The page may have been loaded before the intended dimensions were applied, or the run may not be using the same viewport or environment.
Fix: Set the size before driver.get(), log the CSS viewport, and keep the browser mode and runtime details consistent. If necessary, reload after changing dimensions so the page can render at the intended size.
The screenshot is blank, incomplete or missing visual assets
Cause: Capture may occur before the page or the specific visual content your test needs is ready.
Fix: Wait for an application-specific readiness condition before saving the screenshot. A fixed viewport does not control when a page finishes rendering.
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1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minuteA headless run behaves differently from a headed run
Cause: Headless implementation and browser version are among the environmental factors that can affect rendered output; headless option syntax may also depend on the installed Chrome version.
Fix: Use the option syntax supported by the browser installed in the environment, log whether the run is headless, and validate the viewport and PNG dimensions there rather than assuming desktop results transfer exactly.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Or skip the browser setup
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import requests
r = requests.get(
"https://api.screenshotneo.com/v1/shot",
params={"access_key": "YOUR_API_KEY", "url": "https://stripe.com"},
timeout=90,
)
open("shot.webp", "wb").write(r.content)Equivalent cURL and Node.js calls:
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpconst q = new URLSearchParams({ access_key: 'YOUR_API_KEY', url: 'https://stripe.com' });
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FAQ
Can Selenium save screenshot bytes instead of writing directly to a file?
Yes. Selenium’s Remote WebDriver API provides get_screenshot_as_png(), which returns PNG bytes; use save_screenshot(path) or get_screenshot_as_file(path) when you want Selenium to save a PNG file. Selenium Python Remote WebDriver API
Is CDP viewport emulation portable to Firefox or other browsers?
No. The cited emulation mechanism is part of Chrome DevTools Protocol and is appropriate when a Chromium-specific dependency is acceptable; use WebDriver’s window sizing when portability is the priority.
Frequently Asked Questions
Can Selenium save screenshot bytes instead of writing directly to a file?
Yes. Selenium’s Remote WebDriver API provides get_screenshot_as_png() for PNG bytes, as well as methods to save a PNG file.
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Is CDP viewport emulation portable to Firefox or other browsers?
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