# Subtract Images This function block computes the pixel-wise difference between two images to highlight changes or defects. It is useful for comparison tasks such as detecting deviations from a reference, visual inspection, and motion/change analysis. ## đŸ“Ĩ Inputs `Actual Image` Input socket — the image to be compared (source image). `Reference Image` Input socket — the image to subtract from the actual image (baseline or reference). ## 📤 Outputs `Difference Image` Output socket — resulting image showing the per-pixel difference between the inputs. ## 🕹ī¸ Controls This block has no user-facing controls or widgets. ## 🎨 Features * Produces a visual difference image that emphasizes pixel-level changes between two equally sized images. * Works with color or grayscale images (both inputs must share the same dimensions). * Simple and fast operation suitable as a preprocessing step for downstream detection or logging. ## ⚙ī¸ Running Mechanism When both input sockets provide images, the block produces a `Difference Image` by performing a per-pixel subtraction of the reference from the actual image. The block requires that both images have identical dimensions; if sizes differ, the block will report an error. The difference output can be fed into visualization, thresholding or counting blocks to interpret the result. ## 📝 Usage 1. Connect a source image to the `Actual Image` input socket. 2. Connect a baseline or reference image to the `Reference Image` input socket. 3. Make sure both images have the same size. If not, insert the `Image Resize` block before this block. 4. Use the `Difference Image` output for visualization or further processing. Examples of common workflows: * Visual inspection: connect `Difference Image` to `Show Image` to preview changes. * Binary detection: feed `Difference Image` into `Image Threshold` to create a mask of changed areas. * Quantification: pass the thresholded mask to `Non-zero of Image` to count changed pixels. * Logging: save results with `Image Logger` or `Image Write` for record keeping. ## 💡 Tips and Tricks * Ensure image alignment and resolution match before subtraction. Use `Image Resize` or geometric alignment blocks if needed. * To make subtle differences more visible, apply `Contrast Optimization` or `Normalize Image` to the `Difference Image` before visualization. * Convert the difference to a binary mask using `Image Threshold` to isolate meaningful changes. Combine the mask with `Non-zero of Image` to get a numeric measure of change. * For quick inspection during development, connect the output to `Show Image`. For automated runs, save results with `Image Logger` or `Image Write`. * If you expect single-channel output, check input channel formats (grayscale vs RGB) upstream and convert consistently. ## 🛠ī¸ Troubleshooting * Mismatched image sizes\ Ensure both inputs share the same width and height. Use the `Image Resize` block to resample one of the images. * Very low or no visible difference\ Apply `Contrast Optimization` or `Normalize Image` to amplify small changes, or use `Image Threshold` to create a binary mask. * Unexpected colors or channels\ Confirm both inputs are in the same color space (both grayscale or both RGB) before connecting them. * Need a numeric change measure\ After thresholding the difference, send the mask to `Non-zero of Image` to obtain a count of changed pixels. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.augelab.com/function-blocks/image-transformations/operations/subtract-images.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.