Online Image Glow Effect Tool
Overlay soft blur to create glow. Processing takes place locally in your browser.
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What this tool actually does
Adds a bright glow to one image. Intensity ranges 0..100 percent with step 0.01 and defaults to 25 percent. Kernel size defaults to 5 and is constrained to odd values 3, 5, 7, 9, 11 or 13. There is no glow color, luminance threshold, radius in pixels, blend-mode selector or region mask.
Checkable behavior
The browser computes a square box blur by averaging each RGB channel over the selected neighborhood with nearest-border repetition. It then adds amount/100 of that blurred RGB to the original RGB and clamps output bytes. This is additive glow, not replacement with a blurred image; alpha and dimensions remain unchanged.
Controls, output and limitations
A 3 by 3 example: a black image with center grayscale90 produces blurred center10. At amount0 the output center remains90; at25 percent it becomes approximately92 after byte rounding, and at100 percent it becomes100. Larger kernels spread bright content more widely.
Bright channels can clip to 255, and a dark source produces little visible glow because there is no thresholded bloom extraction. This tool does not create HDR data, neon outlines, AI relighting or editable layers; preserve the source and compare highlights before download.
One browser-decodable image up to 25 MiB and 24,000,000 pixels is processed locally. Press Generate image after changing intensity or kernel, inspect the preview and download PNG named from the source base plus -glow.png. No source-format or metadata preservation is provided.
Both settings have a slider and a numeric field. Kernel size is the side length of the square, not its radius. The RGB average is converted to bytes before the glow is added; the final RGB is converted again. With a 3×3 black image, center 90 and kernel 3, 25% gives exactly 92 because a half-byte tie rounds to the even integer. Alpha is copied unchanged: this cannot create a visible outer glow in a fully transparent background. Each run starts from the loaded source.
One source image is processed at a time, up to 25 MiB (26214400 bytes) and 24000000 pixels. PNG export saves the browser-decoded canvas, not the original encoded file: animation, EXIF and color-profile metadata may be lost or changed. Width and height remain unchanged, but file identity and exact source color representation are not guaranteed. Retain the original.
Processing takes place locally in your browser.