gchq/CyberChef · error · OperationError

Error: Bit argument must be between 0 and 7

Error message

Error: Bit argument must be between 0 and 7

What it means

Thrown by 'View Bit Plane' when the bit-plane argument is outside 0-7. The bit argument selects one of the 8 bits of a colour channel; values outside that range have no valid bit index (the code computes bitIndex = 7 - bit).

Source

Thrown at src/core/operations/ViewBitPlane.mjs:69

    async run(input, args) {
        if (!isImage(input))
            throw new OperationError("Please enter a valid image file.");

        const [colour, bit] = args;
        let parsedImage;
        try {
            parsedImage = await Jimp.read(input);
        } catch (err) {
            throw new OperationError(`Error loading image. (${err})`);
        }

        const width = parsedImage.bitmap.width,
            height = parsedImage.bitmap.height,
            colourIndex = COLOUR_OPTIONS.indexOf(colour),
            bitIndex = 7 - bit;

        if (bit < 0 || bit > 7) {
            throw new OperationError(
                "Error: Bit argument must be between 0 and 7",
            );
        }

        let pixel, bin, newPixelValue;

        parsedImage.scan(0, 0, width, height, function (x, y, idx) {
            pixel = this.bitmap.data[idx + colourIndex];
            bin = Utils.bin(pixel);
            newPixelValue = 255;

            if (bin.charAt(bitIndex) === "1") newPixelValue = 0;

            for (let i = 0; i < 3; i++) {
                this.bitmap.data[idx + i] = newPixelValue;
            }
            this.bitmap.data[idx + 3] = 255;
        });

View on GitHub (pinned to 4290ea7539)

Solutions

1. Set the bit argument to an integer in the range 0-7 inclusive.
2. If your convention numbers bits from the MSB, map it to 7 minus that index.
3. Validate recipe JSON before running when bit is supplied externally.

Example fix

// before
viewBitPlane(input, ["Red", 8]);
// after
viewBitPlane(input, ["Red", 7]);

if (!Number.isInteger(bit) || bit < 0 || bit > 7) {
  throw new Error(`Bit argument must be an integer 0-7, got ${bit}`);
}

function isValidBitPlane(b) { return Number.isInteger(b) && b >= 0 && b <= 7; }

When it happens

Trigger: Setting the bit argument below 0 or above 7 via the Node API or a hand-edited recipe. In the UI the control is a number spinner; a manually crafted recipe can carry an out-of-range value.

Common situations: Programmatically building a recipe with an off-by-one or negative bit index, or mis-translating a 'bit significance' convention (LSB=0 vs MSB=0).

Related errors

• ${this.name} must be greater than or equal to ${this.min}.
• ${this.name} must be less than or equal to ${this.max}.
• IPv4 CIDR must be less than 32
• IPv6 CIDR must be less than 128
• Block out of range.

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/370e3ee651445af0. Report an issue: GitHub.