Automatic
Pixel Ruler

Automatic Pixel Ruler is a Windows desktop tool that overlays real-time pixel measurements on your screen. Using GPU-accelerated screen capture, image pre-processing, and computer vision detection, it automatically identifies rectangular regions and displays their dimensions without any manual drawing.

It runs as a compact, always-on-top panel alongside your other running applications. A full-screen transparent overlay continuously analyses every frame and renders measurement labels directly onto the display.

Key Capabilities

System Requirements

Launching Automatic Pixel Ruler

The main panel opens in the bottom-right corner of your primary monitor. A transparent overlay simultaneously covers the entire screen and begins detecting rectangles.

Quick Start

1. Launch Automatic Pixel Ruler — the overlay becomes active on your primary monitor immediately.
2. Move your mouse over the captured screen. Coloured rectangles will appear around detected UI elements, with dimensions displayed in pixels. The status bar updates with the current captured rectangle count and processing time.
3. Press Ctrl+Shift+X (default) to start or stop a manual line measurement. Press Ctrl+Shift+X again or Esc to cancel this measurement at any time.
4. Press Right Ctrl to save screenshots of highlighted rectangles, if any, to disk.
5. Press Shift+Right Ctrl to save screenshots of all detected rectangles, if any, to disk. Be cautious with this one, as it can generate a large number of files if many rectangles are detected

In the following example, Automatic Pixel Ruler detects the rectangular regions of a Windows Explorer window, including the title bar, address bar, and content area. The dimensions of each detected rectangle are displayed in pixels directly on the screen, allowing you to quickly assess the size of different UI elements without needing to manually draw measurement lines or switch between applications. The Pixel special effect is applied as a pre-processing step to the captured screen image before detection, which simplifies the image and enhances edges of Windows Explorer.

In the next screenshot, Automatic Pixel Ruler detects rectangular regions in a floor plan image. The dimensions of each detected rectangle are displayed in centimeters corresponding to the actual physical size on screen.

Measuring a web page in a browser window

In this example, Automatic Pixel Ruler detects the rectangular regions of a web page displayed in a browser window, including everything: the header, navigation bar, content sections, and images.

In the second image, all detected rectangles dimensions are displayed. Dimensions are shown in in centimers corresponding to the actual physical size on screen.

Measuring an image with heads and faces, with and without pre-processing

In this example, the Oil special effect is applied as a pre-processing step to the captured screen image before detection. This effect simplifies the image and enhances edges, making it easier for the detection algorithm to identify rectangular regions around heads and faces.

This is the exact same image and parameters, but the original captured screen image is shown instead of the pre-processed one. This can be toggled on and off in the interface, using  or  buttons in the title bar, to help you understand how the app is interpreting the screen content and how different pre-processing settings affect detection.

The main window is a compact, horizontally resizable panel with three zones: a title bar with app info and controls, a property grid for tuning parameters, and a status bar with a live readout of detected rectangle count and GPU processing time for the last captured frame.

Window Areas

• Title bar — app title and interactive icons for key functions and dialogs:

   About dialog with system info for diagnostics, this help page, Microsoft Store link, and credits.

   Settings dialog with parameters, plus options to save and load tuning parameters presets to and from .apixruler files.

   Reset all settings to their default values.

   or  Pause or resume screen capture and detection. When paused, the overlay and all labels disappear, and GPU processing is reduced. The app continues to run, allowing you to adjust settings or move the window without the overlay getting in the way.

   or  Show or hide the dimensions of detected rectangles in the overlay. When dimensions are hidden, only the rectangle borders are shown, without any text labels. This can be useful if you want to see the detected shapes without the clutter of dimension labels. The effect is immediately visible in the overlay.

   or  Show pre-processed or original desktop image in the overlay. When enabled, the overlay displays the image after pre-processing steps (blurring, posterization, special effects, etc.) instead of the raw screen capture. This can help you understand how the app is interpreting the screen content and how different pre-processing settings affect detection. The effect is immediately visible in the overlay.

• Property grid — all tuning sliders and toggles, live-editable. Drag the column splitter to resize name/value columns.
• Status bar — throttled readout of detected rectangle count and GPU processing time for the last captured frame.

How it works

Before diving into detailed explanations of each setting, let's take a high-level look at how Automatic Pixel Ruler captures and processes screen data to detect rectangles in real time:

• Real-Time Capture: The app captures the screen content of the selected display(s) at a high frame rate using GPU-accelerated techniques. This allows it to grab raw pixel data with minimal latency and CPU overhead.
• Pre-Processing: Each captured frame undergoes a series of image processing steps to enhance features relevant for rectangle detection. This can include blurring to reduce noise, posterization to simplify colors, and special effects that can help highlight edges.
• Rectangle Detection: The pre-processed image is fed into a computer vision algorithm that identifies rectangular shapes based on edge detection and contour analysis. Detected rectangles are filtered based on size and other parameters to ensure relevance.
• Overlay Rendering: The app renders an always-on-top transparent overlay that draws borders and dimension labels around the detected rectangles directly on the screen. This overlay updates in real time as you move your mouse and interact with applications, giving you continuous feedback on detection performance and screen activity.

1

Title Bar

2

Adaptive or Fixed Sampling

3

Detection parameters

4

Input Display or All Displays

5

Pre-Processing parameters

6

Special Effects
with variable parameters

7

Status Bar

💡 In addition to dragging sliders, values can be edited clicking on a number before the slider, and typing.
When a value is being edited, pressing Up or Down arrow increments or decrements this value by 1, providing fine control.

1

Title Bar — Get to About, Help Microsoft Store, Settings, Reset Settings, Pause / Resume capture. Drag to reposition the window, like any Window on the desktop.

2

Adaptive or Fixed Sampling — With adaptative Sampling on (by default), processing frequency auto-adjusts based on elapsed capture time. When off, fixed sampling is defined by the minimum interval between frames.

⚠️ Very low Fixed Sampling values can raise CPU/GPU load significantly. Keep Adaptive Sampling on unless you need consistent frame intervals.

4

Input Display — Selects which monitor's input to capture (here: DELL U2715H). This option appears only when two or more displays are connected. You can choose to capture a single display or all connected displays.

7

Status Bar — Live readout of detected rectangle count and GPU processing time for the last captured frame. Updated in real time as you move your mouse and interact with applications, giving you continuous feedback on detection performance and screen activity.

3

Detection Parameters

Min Detection Area — Specifies the minimum side length a rectangle must have to be detected and displayed.

Rectangles smaller than this threshold are ignored, which helps filter out tiny or irrelevant shapes.

The default is 30 px. In this case, it is set to 74 px, meaning rectangles smaller than 74 × 74 = 5476 pixels (regardless of exact width and height) will be filtered out.

Edge Thresholds — Edge Thresholds — These define the hysteresis bounds used in edge detection, with values ranging from 0 to 255.

strong threshold determines the minimum intensity for a pixel to be considered a definite edge. Pixels above this value are always treated as edges.

weak threshold sets the minimum intensity for pixels that might be edges.

Pixels between the weak and strong thresholds are only considered edges if they are connected to strong edges. This hysteresis mechanism helps reduce noise and broken edges: weak, isolated pixels are ignored, while weak pixels connected to strong edges are preserved. Default values are Strong = 100 / Weak = 50 (as shown here), which balance edge sensitivity and noise suppression. Adjusting these values can make the detection more sensitive (lower thresholds) or more selective (higher thresholds) depending on the captured image.

5

Pre-Processing Parameters

Luma Posterization — Brightness quantisation (0–64). It merges areas of similar brightness before edge detection, which can help simplify the captured image and highlight major edges while ignoring minor brightness variations.

Chroma Compression — Colour quantisation (0–32). It reduces the variety of colors in captured the image, which helps produce cleaner and more defined edges by minimizing subtle color variations.

💡Level 3 usually gets down to grayscale, which can be useful for certain input styles.

Blur — It applies a Gaussian blur smoothing effect to the captured image, which can help reduce noise and minor details that might interfere with edge detection.

Blur Radius controls the strength of the blur effect, with higher values creating a more pronounced blur. However, excessive blurring can cause edges to become too soft and less defined, so it's important to find a balance that reduces noise without losing important edge information.

Blur Quality controls the quality of the blur effect, with higher values producing a smoother and more visually appealing result at the cost of increased processing time.

Sketch — It applies a sketch-like effect to the captured image, which can help enhance edges and contours by creating a stylized representation of the screen content.

Sketch Size controls the size of the area used to compute the sketch effect, with higher values creating a more pronounced stylized effect.

Sketch Strength controls how much the sketch effect emphasizes edges, with higher values making edges more pronounced in the stylized image.

6

Pre-Processing Special Effects Parameters

None — No special effects applied. The captured image is processed with the standard pre-processing steps (blurring, posterization, chroma compression) without any additional transformations.

Pixel — Applies a pixelation effect to the captured image before edge detection.

Block Size controls the size of the pixel blocks, with higher values creating a more pronounced pixelation effect.

Oil — Applies an oil painting effect to the captured image before edge detection. This effect creates a stylized, smoothed version of the screen content, which can help emphasize larger shapes and reduce noise from fine details.

Paint Radius controls the size of the area used to compute the oil painting effect, with higher values creating a more pronounced smoothing effect.

Paint Details controls how much detail is preserved in the oil painting effect, with higher values retaining more of the original image's details while still applying the stylized effect.

Sampling Quality controls the quality of the oil painting effect, with higher values producing a smoother and more visually appealing result at the cost of increased processing time.

⚠️ High Paint Radius, Paint Details, or Sampling Quality values can significantly increase GPU processing time, which may lead to lower frame rates and higher latency in detection.

Crystal — Applies a crystal-like distortion effect to the captured image before edge detection.

Cell Size controls the size of the crystal cells, with higher values creating a more pronounced distortion effect.

Edge Emphasis controls how much the effect emphasizes edges, with higher values making edges more pronounced in the distorted image.

The overlay is a full-screen transparent window sitting above all other windows, updated in real time. It captures the active display and processes frames, runs edge detection, and draws results. All Automatic Pixel Ruler windows are themselves excluded from screen recording and capture.

Automatic Rectangle Detection

Automatic Pixel Ruler continuously processes incoming frames from input displays. Rectangles meeting the minimum area threshold get a coloured border and a pixel-dimension label — e.g. 320 × 48. Each rectangle gets a unique color from its screen position so labels stay visually distinct.

Overlay & Input

When Automatic Pixel Ruler is running, the overlay is fully transparent to user input—mouse clicks and keyboard actions pass through to underlying windows. This allows you to interact with applications as normal while still seeing the measurement overlays on top. You can hover over buttons, menus, or any UI element, click anywhere or use the keyboard, to see captured rectangles list evolve in real-time.

Highlights

All rectangles detected under the mouse pointer are highlighted. A highlighted rectangle has a thicker border and a larger label displaying its dimensions (width and height). For example, if the label shows 640 × 480 (2/5), it means this is the second rectangle, sized 640 pixels wide by 480 pixels high, out of five rectangles currently highlighted under the mouse pointer.

The list of highlighted rectangles is reset whenever the mouse pointer moves.

At a given mouse position, multiple rectangles may be detected (for example, a button inside a panel). However, only one rectangle is shown with a semi-transparent fill (of the same color as its border) to make it visually stand out as the active highlight. The active highlight is the last rectangle drawn, so it appears on top of the others.

Press Left Ctrl to cycle through the rectangles detected under the mouse pointer. Each press moves the active state to the next highlighted rectangle in the list.

Manual Line Measurement

In addition to automatic rectangle detection, you can measure the pixel distance between any two points on the screen by entering Manual Line Measurement mode. This is useful for measuring non-rectangular spans or verifying dimensions that may not be automatically captured as rectangles.

1. Press Ctrl+Shift+X or the shortcut you have defined if you changed default settings. Your cursor position is recorded as the start point.
2. Move the mouse anywhere. A live line is drawn with a bounding-rectangle dimension label.
3. Press the shortcut again or Esc to cancel.

Saving Rectangles Screenshots

Press Right Ctrl to save PNG images of all rectangles currently highlighted under the mouse pointer. Each highlighted rectangle is captured and exported as a separate PNG file. During the saving process, the overlay window may pause briefly while the images are being generated and written to disk. This pause is normal and typically lasts only a short moment, depending on the number and size of the rectangles being saved.

Press Shift+Right Ctrl to save PNG images of all rectangles. Be cautious with this option, as it can generate a large number of files if many rectangles are detected on the screen.

The default file name format is Automatic Pixel Ruler, followed by the current date, an Automatic counter that resets daily, and, if multiple rectangles are highlighted under the mouse pointer, the index of the highlighted rectangle.

Click ⚙ in the title bar to open Settings dialog:

From there you can:

• Save tuning parameters as an ..apixruler file
• Load tuning parameters from an .apixruler file
• Change the keyboard shortcut for manual line measurement mode
  💡if an incorrect key combination is entered, the app will show an "Invalid shortcut" error and keep the previous shortcut.
• Define the unit used to display dimensions in labels (pixels, inches, centimeters, or millimeters).
  
  Except for pixels, all units are calculated using the current display’s raw DPI, so they correspond to real-world physical sizes regardless of screen resolution or scaling. When All displays is selected as capture input, the DPI used to show dimensions is that of the display containing the largest portion of the dimensions' rectangle.
  
  ⚠️ The display's raw DPI is determined by the display's hardware EDID information. If this information is unavailable, which can happen on some old monitors or virtual machines, the Windows effective DPI is used, which may lead to inaccurate real-world measurements.

Resetting Settings

Click  in the title bar and confirm to restore all visual tuning parameters to factory defaults. Other non-visual settings (such as dimensions unit, etc.) are not affected.

Settings File

Configuration is stored at:

This file is updated automatically on change and on close. A 30-day rolling backup of it is maintained int the settings.bak directory aside it. Close the application and delete settings.json to reset everything to defaults.

Screenshots

Saved as PNG files in the configured Save Directory (default: Pictures\Screenshots). Filenames encode the app name, date, and an incrementing counter.

Tuning Profiles

Individual parameter sets can be saved as .apixruler files (JSON format). Share between machines or keep as presets for different workflows.

.apixruler files can be associated with Automatic Pixel Ruler, allowing you to double-click them in Windows Explorer to load specific tuning profiles. This is useful for quickly switching between different detection configurations for various tasks or sharing settings with others.

Optimisation Tips

• Missing small UI elements? Lower Min Rectangle Area and Weak Edge Threshold.
• For a more stylized detection that emphasizes larger shapes, experiment with Pre-Processing parameters and Special Effects.
• If the overlay feels too cluttered, try increasing Min Rectangle Area or adjusting edge thresholds to filter out less relevant rectangles.
• If you want to focus on specific types of UI elements, try using the Special Effects to enhance certain features in the captured image, which can help the detection algorithm identify relevant rectangles more effectively.
• Feel sluggish? Try disabling resource-intensive special effects like Oil or increasing their parameters to reduce GPU load, or lower the resolution of your display if possible.
• For precision layout work, use Manual Line Measurement alongside automatic detection.
• Use the Show Pre-Processed Image toggle to see how different pre-processing settings affect the captured image and detection results, which can help you fine-tune parameters for optimal performance. This is especially useful when experimenting with the various pre-processing effects, as it allows you to visually understand how each effect transforms the captured image and influences edge detection.
• For best performance, keep Adaptive Sampling enabled. If you prefer a fixed capture rate, set Fixed Sampling to a value that balances responsiveness and CPU/GPU load.

.apixruler files

• You can store different .apixruler profiles for various use cases, such as one for UI design with high sensitivity and another for general screen measurement with more conservative settings. Some settings are better for bitmap images (e.g. Blur, Oil or Pixel processor), while others work better for vector-rendered UI . Save these as separate .apixruler files for easy switching.
• You can also share .apixruler files with colleagues or the community to exchange tuning configurations for specific applications or workflows.
• In Windows .apixruler files can be associated with Automatic Pixel Ruler, allowing you to double-click them in Windows Explorer to load specific tuning profiles.
  
  To associate .apixruler files with Automatic Pixel Ruler, right-click any .apixruler file in Windows Explorer, select "Open with" > "Choose another app", then select Automatic Pixel Ruler from the list and check "Always use this app to open .apixruler files".

Troubleshooting

Click  in the title bar to open About dialog:

From there you can:

• Open a System Info window to send to support for troubleshooting
• Open this User Guide
• Go to the Microsoft Store page to leave a review, get support, or purchase the app if you haven't already