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To convert HTML to an image in Ruby on Rails, render the page in a real browser engine and capture its pixels. Rails can produce the HTML, but it does not turn that HTML into a screenshot by itself. For direct Ruby control, use Ferrum with Chrome or Chromium; choose the viewport, full page, or a specific element, then return or store the captured image.
Choose the right rendering path
Start by deciding what your input is and where you want the browser to run. Rendering a Rails template gives you HTML; a browser is still needed to apply CSS, load fonts and images, execute JavaScript, and produce pixels.
| Option | Best fit | Tradeoff |
|---|---|---|
| Ferrum directly | Ruby code that needs control over Chrome/Chromium screenshots. | Your team manages the browser runtime and integration. Ferrum project |
| FerrumPdf | A Rails controller workflow that benefits from a screenshot wrapper. | Check compatibility with your Rails version and workload before adopting it. FerrumPdf project |
| Cuprite | An application already using Capybara browser workflows. | Cuprite is a Capybara driver built on Ferrum, and is not necessary just to call Ferrum’s screenshot API. Cuprite project |
| ScreenshotNeo | A hosted screenshot API when you would rather not install and operate Chrome in your Rails environment. | The request goes to an external service, so review your data-handling needs. |
| HTML2IMG | A hosted HTML-to-image API with published Ruby and Rails integration material. | It adds an external service and request; comparative privacy, reliability, and cost were not established in the material reviewed. HTML2IMG and its Rails guide |
Render Rails HTML with Ferrum
Ferrum controls Chrome or Chromium through the Chrome DevTools Protocol. Its project README says, “All you need is Ruby and Chrome or Chromium.” You need both a usable browser binary and Ruby code that opens the document and captures it. See the Ferrum README for its current installation and API details.
Install and configure the dependencies
Add the Ferrum gem to the application bundle using the version and installation instructions in the project’s current documentation. Install Chrome or Chromium in the environment where the Rails process will run. If the browser executable is not discoverable on PATH, configure Ferrum to use its actual executable location using the option supported by the installed version.
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Do not assume that a browser available on a developer laptop is also present in a production container. Test the exact production-like image, including its browser path and sandbox configuration. Cuprite documents a Docker example with a no-sandbox browser option; that is deployment-specific guidance, not a universal security setting. Review any sandbox change against your container’s security requirements. Cuprite README
Render a view and capture the page
The following Rails controller action renders a view to a string, loads it as a document, and captures a PNG. It illustrates the flow; adapt error handling, browser configuration, and asset access to your application and installed Ferrum version.
class CardsController < ApplicationController
def screenshot
html = render_to_string(
template: "cards/show",
layout: "application",
formats: [:html]
)
browser = Ferrum::Browser.new
begin
browser.go_to("data:text/html;charset=utf-8,#{ERB::Util.url_encode(html)}")
browser.screenshot(path: Rails.root.join("tmp", "card.png").to_s)
ensure
browser.quit
end
send_file Rails.root.join("tmp", "card.png"),
type: "image/png",
disposition: "inline"
end
endFor production use, check the Ferrum documentation for the precise navigation and screenshot signatures supported by your installed release. A data URL is convenient for a self-contained document, but it can be a poor fit when the HTML references relative asset paths: there is no ordinary Rails page URL to resolve them against. Use absolute, reachable asset URLs, inline required assets, or load the document at a URL whose origin and paths make sense. Ensure that any private application data included in the rendered HTML is handled appropriately.
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When rendering a template for an image, include the layout and styles the image needs. Verify that fonts, stylesheets, and images can be reached by the browser process; a URL that works in the user’s browser may not be reachable from a server-side renderer. If the view depends on JavaScript, wait for an application-specific signal that the relevant content has rendered before taking the screenshot. There is no universal readiness delay that works for every page.
Choose image format and capture bounds
Ferrum documents PNG, JPEG/JPG, and WebP output. PNG is its documented default; choose a format explicitly when the consumer expects something else. PNG is useful when you need lossless output, while JPEG or WebP may suit a downstream system that accepts those formats and your quality requirements. The available controls also include scale, background color, file output, and base64 return. Ferrum screenshot documentation
Viewport, full page, selector, or area
- Viewport: captures the visible browser viewport. Set the viewport dimensions to the output dimensions you need.
- Full page: captures the whole document, which may create a very tall image. Confirm that the consumer can display or process the resulting dimensions.
- CSS selector: captures a chosen element, useful for a card, chart, or component.
- Coordinate area: captures a specified region when a selector is not the right boundary.
Ferrum supports viewport and full-page capture as well as selector- and coordinate-area capture. Pick the bounds deliberately: relying on defaults can produce a screenshot with the wrong dimensions or more page content than intended. Ferrum project
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Return the image safely from Rails
The example writes to a fixed temporary filename to keep the code readable, but concurrent requests can overwrite one another’s files. In an application that captures on demand, use a unique temporary path or an appropriately managed storage destination, and clean up temporary files after serving them. For repeated or expensive captures, consider moving rendering off the request path so browser startup and page rendering do not determine a user’s request latency. That is an architectural choice; the project documentation does not establish a performance benchmark or one best deployment pattern.
For simpler one-off actions, Rails can send a generated file with an image MIME type such as image/png. If the response is generated in memory, return the binary bytes with the matching content type instead. Keep the output format and response MIME type in agreement, and avoid logging rendered HTML or image contents if they contain sensitive information.
Use a Rails wrapper or an existing Capybara setup
FerrumPdf for controller-driven screenshots
FerrumPdf documents a Rails controller renderer and a render_screenshot interface that accepts HTML or a URL. Its wrapper exposes options including format, full-page capture, selector, area, scale, and background color. This may reduce controller integration glue, but the project description alone does not establish compatibility with every Rails version or workload. Verify its current requirements and behavior before making it part of an application. FerrumPdf project
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Cuprite when Capybara is already in the stack
Cuprite is relevant when your application already uses Capybara or needs a Capybara-driven browser workflow. If the only requirement is to call Ferrum’s screenshot API, adding Capybara is not required. Check Cuprite’s current setup guidance and treat its Docker browser options as specific to that deployment rather than a blanket recommendation. Cuprite documentation
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ScreenshotNeo offers a hosted API for returning an image or PDF from a URL. This example captures a publicly reachable page; see the ScreenshotNeo API documentation for current parameters and response details.
curl -G "https://api.screenshotneo.com/v1/shot"
-d access_key=YOUR_API_KEY
--data-urlencode url=https://stripe.com
-o shot.webpScreenshotNeo removes cookie/consent banners, newsletter popups, and chat widgets before capture, with each cleanup step configurable. Bot checks, blank pages, and failed loads are never billed. Its MCP server provides screenshot tools for AI agents, and the Free plan includes 1,000 screenshots per month with no card; paid plans start at $5 for 3,000. Consider it when an external renderer fits your data-handling requirements and you prefer not to manage Chrome in your Rails environment.
Sign up for ScreenshotNeo’s free plan to try 1,000 screenshots a month with no card.
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Hosted HTML input and data-handling considerations
ScreenshotNeo’s one-call example accepts a URL. For HTML that exists only as a Rails-rendered string, use a browser-based path such as Ferrum, or assess a hosted provider whose documented interface accepts HTML. HTML2IMG publishes Ruby and Rails material for sending HTML to a hosted endpoint and receiving an image URL; its Rails guide describes API-key configuration. Before sending content to any external service, determine whether the HTML contains data that must remain within your infrastructure, and review that provider’s current terms and handling practices. The cited material does not establish a comparative privacy, availability, or cost assessment.
Troubleshooting common failures
- Ferrum cannot start the browser: Chrome/Chromium may be missing or the executable may not be discoverable. Install the browser in the runtime environment and configure its path as needed.
- The capture is blank or styles are missing: Check that the rendered document includes the expected layout and that CSS, fonts, and images resolve from the browser’s environment. Relative links loaded from a data URL are a common source of missing assets.
- JavaScript content is absent: The capture may occur before client-side rendering finishes. Wait for the specific selector or application signal that means the needed content is ready rather than relying on a fixed delay.
- The image has unexpected dimensions: Set the viewport or choose full-page, selector, or area capture explicitly. Full-page output can be much taller than a typical fixed-size image.
- The browser fails in a container: Compare the container’s browser installation, executable path, and sandbox settings with a known working environment. Do not adopt a no-sandbox option without evaluating the security implications.
- Requests return the wrong or corrupted output: Match the screenshot format to the response content type, and ensure the response sends the binary image rather than encoded or logged text.
- Concurrent requests serve the wrong file: Avoid a shared fixed temporary filename. Use unique paths or a storage workflow designed for concurrent jobs.
Frequently Asked Questions
Can Rails convert a template to an image without Chrome or Chromium?
Not with the browser-rendering approach described here: Rails renders HTML, while a browser engine applies layout and captures pixels. Ferrum requires Chrome or Chromium; a hosted service is an alternative if external processing suits your requirements.
Do I need Capybara to take a Ferrum screenshot?
No. Cuprite is useful for Capybara-driven browser workflows, but Ferrum’s screenshot API can be used directly.
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Yes. Ferrum documents capture by CSS selector or coordinate area, in addition to viewport and full-page screenshots.
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