keras-team/keras · error · ValueError

`brightness_range should be tuple or list of two floats. Rec

Error message

`brightness_range should be tuple or list of two floats. Received: {brightness_range}

What it means

brightness_range, if given, must be a tuple or list of exactly two elements (typically floats bounding the random brightness shift).

Source

Thrown at keras/src/legacy/preprocessing/image.py:1082

                    "`featurewise_std_normalization`, "
                    "which overrides setting of "
                    "`featurewise_center`."
                )
        if samplewise_std_normalization:
            if not samplewise_center:
                self.samplewise_center = True
                warnings.warn(
                    "This ImageDataGenerator specifies "
                    "`samplewise_std_normalization`, "
                    "which overrides setting of "
                    "`samplewise_center`."
                )
        if brightness_range is not None:
            if (
                not isinstance(brightness_range, (tuple, list))
                or len(brightness_range) != 2
            ):
                raise ValueError(
                    "`brightness_range should be tuple or list of two floats. "
                    f"Received: {brightness_range}"
                )
        self.brightness_range = brightness_range

    def flow(
        self,
        x,
        y=None,
        batch_size=32,
        shuffle=True,
        sample_weight=None,
        seed=None,
        save_to_dir=None,
        save_prefix="",
        save_format="png",
        ignore_class_split=False,
        subset=None,

View on GitHub (pinned to 7a34a03db6)

Solutions

1. Use brightness_range=[0.5, 1.5] (2 elements, tuple or list)
2. Omit it for no brightness augmentation

Example fix

// before
ImageDataGenerator(brightness_range=0.5)
// after
ImageDataGenerator(brightness_range=[0.5, 1.5])

assert brightness_range is None or (isinstance(brightness_range,(list,tuple)) and len(brightness_range)==2)

def br_ok(b): return b is None or (isinstance(b,(list,tuple)) and len(b)==2)

try: ImageDataGenerator(brightness_range=b)
except ValueError as e: if 'brightness_range' in str(e): b = [0.5, 1.5]

When it happens

Trigger: ImageDataGenerator(brightness_range=0.5) (scalar) or brightness_range=[0.5,1.5,2.0].

Common situations: Assuming scalar like zoom_range; YAML tuple parsed as list of wrong length.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• `factor` argument cannot have an upper bound lesser than the
• `factor` argument must have values larger than -1. Received:
• `factor` argument cannot have an upper bound less than the l
• `zoom_range` should be a float or a tuple or list of two flo
• Unknown activation function '{activation}' cannot be seriali

AI-assisted analysis of keras-team/keras@7a34a03db6 (2026-08-25). Data as JSON: /api/errors/a079c08caddf9c96. Report an issue: GitHub.