# Color Enhancement

## Evaluate Expression

Added in version 0.4.1.

Pixel channels can be manipulated by applying an arithmetic, relational, or logical expression. See `EVALUATE_OPS` for a list of valid operations.

For example, when given image `enhancement.jpg`:

We can reduce the amount of data in the blue channel by applying the right-shift binary operator, and increase data in the right channel with left-shift operator:

    from wand.image import Image

    with Image(filename='enhancement.jpg') as img:
        # B >> 1
        img.evaluate(operator='rightshift', value=1, channel='blue')
        # R << 1
        img.evaluate(operator='leftshift', value=1, channel='red')

## Function Expression

Added in version 0.4.1.

Similar to `evaluate()`, `function()` applies a multi-argument function to pixel channels. See `FUNCTION_TYPES` for a list of available function formulas.

For example, when given image `enhancement.jpg`:

We can apply a Sinusoid function with the following:

    from wand.image import Image

    with Image(filename='enhancement.jpg') as img:
        frequency = 3
        phase_shift = -90
        amplitude = 0.2
        bias = 0.7
        img.function('sinusoid', [frequency, phase_shift, amplitude, bias])

## Gamma

Added in version 0.4.1.

Gamma correction allows you to adjust the luminance of an image. Resulting pixels are defined as `pixel^(1/gamma)`. The value of `gamma` is typically between 0.8 & 2.3 range, and value of 1.0 will not affect the resulting image.

The `level()` method can also adjust `gamma` value.

For example, when given image `enhancement.jpg`:

We can step through 4 pre-configured gamma correction values with the following:

    from wand.image import Image

    with Image(filename='enhancement.jpg') as img_src:
        for Y in [0.8, 0.9, 1.33, 1.66]:
            with Image(img_src) as img_cpy:
                img_cpy.gamma(Y)

## Level

Added in version 0.4.1.

Black & white boundaries of an image can be controlled with `level()` method. Similar to the `gamma()` method, mid-point levels can be adjusted with the `gamma` keyword argument.

The `black` and `white` point arguments are expecting values between 0.0 & 1.0 which represent percentages.

For example, when given image `enhancement.jpg`:

We can adjust the level range between 20% & 90% with slight mid-range increase:

    from wand.image import Image

    with Image(filename='enhancement.jpg') as img:
        img.level(0.2, 0.9, gamma=1.1)
        img.save(filename='enhancement-level.jpg')