Extract WebP Alpha Channel
Pull the alpha channel out of a WebP - as transparent-black, viewable grayscale, or hard binary mask. Free, offline, client-side, instant, secure.
Pull the transparency (alpha) channel out of a WebP image and see it next to the original. View it as a grayscale map, a hard black-and-white mask with an adjustable threshold, or keep the raw alpha on transparent black - then download the result as WebP.
Original
Alpha channel
How to Use Extract WebP Alpha Channel
- Choose a WebP file. The tool reads it locally via the File API - nothing uploads. Max 20 MB.
- Pick a mode. "Transparent-black" is the literal alpha channel: each pixel's RGB becomes black, the alpha value is unchanged. Looks empty on a transparent page; composites correctly. "Grayscale" makes the alpha viewable:
(α, α, α, 255)- opaque output where white = source-opaque and black = source-transparent. "Binary" produces a hard mask: any alpha above the threshold becomes white opaque, anything below becomes black opaque. - For Binary mode, tune the threshold with the slider (0-255). 128 is a sensible default; lower values keep more pixels white; higher values keep fewer.
- Read the stats line. Dimensions, count of fully opaque pixels (alpha=255), fully transparent pixels (alpha=0), and partially transparent (alpha between 1 and 254). Percentages of each. The mode used.
- Hit Download. The output is named after your source file with an
-alpha,-alpha-grayscale, or-alpha-binarysuffix. Ctrl/Cmd + Enter also triggers download. - Try Reset. Switches the mode back to transparent-black with the default threshold, keeping the loaded image.
Frequently Asked Questions
What is an alpha channel?
A per-pixel transparency value, stored alongside red, green, and blue. Alpha is 0 for fully transparent, 255 for fully opaque, and anywhere in between for partial transparency. WebP, PNG, and modern image formats all support it. JPEG does not – JPEG is opaque-only.
What’s the difference between the three modes?
Transparent-black sets RGB to 0 and keeps alpha exactly as is. This is “the alpha channel” in the strict sense – the output IS just the alpha – but it renders invisibly against any transparent background. Grayscale copies alpha to RGB (so opaque pixels become white, transparent pixels become black) and sets output alpha to 255. This is the human-viewable form. Binary applies a threshold to alpha: above ⇒ white opaque; below ⇒ black opaque. Useful when you need a hard 1-bit mask.
Why did my image turn completely black in transparent-black mode?
That mode sets RGB to 0 unconditionally. If your source image is fully opaque (alpha=255 everywhere – common for camera JPEGs converted to WebP), the result is an opaque black rectangle. The transparency information is preserved (it’s just “all opaque”), but visually you see solid black. Switch to Grayscale mode to confirm there’s no transparency to extract – you’d see solid white.
Is Grayscale or Transparent-black “more correct”?
Both are correct, just different representations. The actual stored data is identical – alpha values from 0 to 255. Transparent-black preserves the data in the alpha channel of an RGBA image; Grayscale rebroadcasts it to RGB so you can see it. Most other tools default to grayscale (it’s what GIMP’s “Decompose to Alpha” produces, for example), which is why we offer it.
What’s the threshold slider for?
Only used in Binary mode. The threshold value (0-255) is the cutoff: each pixel’s alpha is compared against it. Above ⇒ white opaque; below ⇒ black opaque. At threshold=0, every pixel except fully-transparent ones becomes white. At threshold=255, only fully-opaque pixels become white. The default 128 captures pixels that are more opaque than transparent.
What about non-WebP images?
The tool rejects non-WebP files because the title and FAQ promise WebP specifically. The same algorithm works on any image format the browser can decode – PNG and AVIF also have alpha channels. If you need to extract alpha from a PNG, convert it to WebP first using any image converter, or use our image-format converter.
How large can the image be?
20 MB upload cap. Practically the canvas is limited to about 16,384 pixels per side; larger images hit browser caps. The filter is O(pixels), so a 4K image (about 8M pixels) processes in around 100 ms.
Is my image uploaded to a server?
No. The page loads three static files (HTML, CSS, JS) and then runs entirely in your browser via the File API and Canvas. Your image bytes never leave the device – no fetch, no XHR, no analytics, no cookies. You can disconnect from the internet after the page loads and the tool still works.
Is this tool free?
Yes – free, unlimited, no signup, no watermark. The extracted alpha image is yours to use anywhere. Attribution to is appreciated but not required.