A grayscale version can be useful for a document, a restrained website asset or a comparison where colour is distracting. It replaces colour with tonal values while keeping many shades between black and white.
Grayscale Image uses PHP GD's grayscale filter. It keeps the source dimensions and can retain transparency in an appropriate output format.
Grayscale still contains shades
A photograph with coloured clothing becomes a photograph with different grey tones. It does not become a two value black and white scan. Use Threshold when that separate treatment is actually needed.
Two colours can become similar in grayscale even if they looked distinct in the original. A chart that relies on red and green categories may therefore become harder to understand after conversion.
The filter's luminance handling should be judged from the resulting pixels. This guide does not assign an exact grey value to every input colour because library behaviour is what the tool actually uses.
Review meaning as well as appearance
Coloured highlights, map keys and status indicators can carry information. Remove colour only when the remaining labels and tones still make the image understandable.
The operation does not remove metadata selectively, perform OCR or make a faded scan readable automatically. Like the rest of the image tools, its output is a fresh encoding without original profiles or comments.
For a grayscale logo, inspect edges on the intended background and choose PNG if alpha is needed. JPEG can be suitable for a photo when its loss of transparency is acceptable.
Keep the colour original. A grayscale download does not retain enough colour information to recreate the source faithfully, even if another editor later applies a tint.