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Canvas Imagedata Height

📅 2026-06-14 | 📂 HTML
## HTML Canvas ImageData `height` Property The `height` property of an `ImageData` object returns the actual height of the image data in pixels. An `ImageData` object represents the underlying pixel data of an area of a `` element. It contains three main properties: `width`, `height`, and `data` (a one-dimensional array containing the RGBA pixel data). --- ## Syntax ```javascript imageData.height; ``` ### Return Value * **Type:** `Number` * **Description:** A read-only integer representing the height of the `ImageData` object in pixels. --- ## Browser Support The `height` property is supported by all modern web browsers: * Google Chrome * Mozilla Firefox * Microsoft Edge / Internet Explorer 9+ * Safari * Opera *Note: Internet Explorer 8 and earlier versions do not support the `` element.* --- ## Code Examples ### Example 1: Getting the Height of an ImageData Object The following example creates an `ImageData` object using the `createImageData()` method and outputs its height to the console. ```javascript const canvas = document.getElementById("myCanvas"); const ctx = canvas.getContext("2d"); // Create an ImageData object with a width of 200px and height of 150px const imgData = ctx.createImageData(200, 150); // Output the height of the ImageData object console.log("Height of imgData is: " + imgData.height); // Output: 150 ``` ### Example 2: Interactive Canvas Pixel Manipulation In this practical example, we retrieve the `ImageData` from an existing canvas, read its `width` and `height` properties, and use them to loop through and manipulate the pixel data. ```html ``` --- ## Technical Considerations ### 1. Read-Only Property The `height` property of an `ImageData` object is **read-only**. You cannot resize an `ImageData` object by manually changing its `height` property. Attempting to write to it will either fail silently or throw an error in strict mode. ```javascript const imgData = ctx.createImageData(100, 100); imgData.height = 200; // This will have no effect console.log(imgData.height); // Still outputs 100 ``` ### 2. Relationship with High-DPI Displays (Retina Screens) The `height` of the `ImageData` object represents the actual number of physical pixels in the image data array. On high-DPI (Retina) displays, the physical pixel dimensions of the canvas backing store may be larger than the CSS dimensions of the `` element. ### 3. Related Canvas Methods To fully utilize `ImageData` objects, you should also refer to the following Canvas 2D API methods: * **`createImageData()`**: Creates a new, blank `ImageData` object with the specified dimensions. * **`getImageData()`**: Returns an `ImageData` object containing the pixel data for a specified portion of the canvas. * **`putImageData()`**: Paints data from a given `ImageData` object back onto the canvas.
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