Generate Random Bitmap

Each pixel here is drawn independently of its neighbours, which makes the image white noise: the snow on an untuned analogue TV, or the grain test pattern used to check a display or an image pipeline. There are no shapes, gradients or edges on purpose; any clusters you see are chance.

That is different from the "noise" used for clouds, terrain and marble textures. Perlin, simplex and value noise blend random values smoothly across space, so neighbouring pixels are similar. If you want soft, organic texture, white noise is the wrong starting point; blurring it helps only a little.

In black-and-white mode, Black pixels (%) sets the density. At 50% you get static; at 5 to 10% you get scattered dots, the "salt and pepper" pattern used to test denoising filters. In My colours mode each colour is equally likely, so add a colour twice to make it twice as common.

"Bitmap" usually just means an image made of pixels, so for websites, documents and image editors, take the PNG. It is lossless, works everywhere and is never larger than it needs to be.

Take the BMP when something specifically asks for a .bmp file: older Windows software, some embedded displays and microcontroller libraries, or your own code, where an uncompressed format with a fixed header is easy to read byte by byte. Its size is predictable from the dimensions alone, as the tile above shows.

Avoid JPEG for noise. Lossy compression smears random pixels into blocks and ringing, and still produces a large file, so you lose the noise and gain nothing.

Leave Seed empty and every image is new, drawn from your browser's secure random source. Type any text, such as test-001, and the page switches to a seeded generator (sfc32): the same seed, size and colour settings always produce exactly the same pixels, on any device.

That is useful when an image is a test fixture. You can regenerate the identical input for a resize or compression test instead of storing the file, compare a filter's output before and after a code change, or tell a colleague "seed test-001, 256 × 256, grayscale" instead of sending an attachment. Changing the size changes the image, because the pixels are read from the sequence row by row.

Seeded output is predictable by design, so don't use it where unpredictability matters. The seed is only used in your browser and is not part of the downloaded file.

A 16 × 16 image is tiny on screen. Enlarging it with ordinary smooth resizing blends neighbouring pixels into a blur. To keep hard square edges, enlarge by a whole number using nearest-neighbour scaling, which is what Download scale does: 16 × 16 at 16× gives a 256 × 256 file where each original pixel is a 16 × 16 block.

• CSS: image-rendering: pixelated; on the img keeps a small image sharp when the browser scales it up.
• Photoshop: Image Size, resample with Nearest Neighbor (hard edges).
• GIMP: Scale Image with Interpolation set to None.

Whole-number scales matter. At 1.5× some pixels become two pixels wide and others one, which makes the grid look uneven.