Joe's Filters: Joe's Levels

The Joe's Levels plugin is a part of Joe's Filters, shareware utility and image processing effects for Final Cut Pro.

What it does

Joe's Levels is a standard five-adjustment Levels adjustment for Final Cut Pro, it works just like Photoshop and yields equivalent results. This is a replacement for the built in Levels filter in Final Cut Pro which never made much sense to me.

In addition to the five standard adjustment controls, Joe's levels adds a complete set of YUV and RGB channel targeting options.

Example Images

Original Image
input black: 25 gamma: 0.6 input white: 255 output black: 0 output white: 255	input black: 75 gamma: 1.2 input white: 240 output black: 0 output white: 255
input black: 50 gamma: 1.0 input white: 255 output black: 0 output white: 255	input black: 0 gamma: 1.0 input white: 200 output black: 0 output white: 255
input black: 0 gamma: 0.7 input white: 255 output black: 0 output white: 150	input black: 0 gamma: 0.7 input white: 255 output black: 125 output white: 255
Original Image
input black: 30 gamma: 1.2 input white: 175 output black: 0 output white: 255 Apply To: RGB	input black: 30 gamma: 1.2 input white: 175 output black: 0 output white: 255 Apply To: Luminance

How To Use Levels

Levels is a fundamental adjustment for digital image processing offering very specific control over image values. Everything that can be done with a conventional Brightness and Contrast control can be done better with Levels.

The Contrast control of a standard Brightness & Contrast adjustment moves the Input Black and Input White equal amounts towards the center. The higher the contrast, the less the distance between the Input Black and White. Levels allows for much more precise adjustment tailored exactly to an image's specific characteristics. Instead of compressing the image's value range equally from both ends, Levels can compress from either direction, or bias the compression towards light or dark.

A conventional Brightness adjustment moves either the Output Black or the Output White towards the middle. A higher brightness value equals a higher Output Black, a darker brightness setting equals a lower Output White. With Levels, the values can be controlled independently, allowing for more or less brightness skewed in either direction.

Gamma bends the gray curve of the image. Changing gamma settings can lighten or darken an image without shifting the highlights and shadows. This adjustment is very similar to having precise control over film response, the photographic term for how a given film stock reproduces a gray ramp. Moving the gamma setting towards black (less than one) will bend the curve and lighten the image by increasing the value space between middle gray and white. Moving gamma towards white (greater than one) will darken the image by increasing the value space between black and middle gray.

The Controls

• Apply To (RGB, Luma, R, G, B, C, M, Y, Chroma, Cb, Cr, Alpha)

  Sets which color channel or channels will be affected.

• Input Black (0 - 253)

  Input black sets the black value in the image. Every value darker than the specified value will become black.

• Gamma (0.1 - 5)

  Gamma describes the bending of the grayscale curve. This has the effect of compressing the values on one side or another. Moving the slider towards white (greater than one) will increase the number of dark values and darken the image, moving towards black (less than one) will increase the number of light values, lightening the image.

  Note: This Gamma value is combined with your image's existing gamma to produce a resulting gamma value. Setting this value to 1.8 does not result in a 1.8 gamma curve unless the starting curve was 1.0, which it probably isn't, unless you have a very wacky monitor.

• Input White (2 - 255)

  This clips the image at the white end of the curve. Every value brighter than the specified value will become white.

• Output Black (0 - 255)

  Specifies the darkest pixel value allowed in the output image. The grayscale ramp will compress with the darkest image pixels remapped to the Output Black value.

• Output White (0 - 255)

  Basically the same as Output Black, except at the other end of the scale. This specifies the lightest pixel value in the image. The Grayscale ramp will compress with the lightest pixels remapped to the Output White value.

Adjusting Chroma

Chroma targeting controls were added mostly for experimentation and to help better understand YUV color.

The chroma component of YUV video doesn't work like a normal light-to-dark channel. The two chroma channels are centered on 128 and create their color by shifting out from the middle. Compressing the Input values evenly will increase the saturation of the image, compressing the Output values will desaturate the image. Adjusting Gamma will shift the hue of the selected channel.

Using Final Cut Pro's New Histogram with Joe's Levels

The new Histogram included with Final Cut Pro 3.0's new Video Scopes is useful but frustrating. While a good start, this long overdue addition can be nearly useless for common levels adjustments.

A histogram is a bar graph of the pixel values in an image. Final Cut Pro's new Histogram seems to base it's height on a linear tally or pixel values instead of a logarithmic tally. Because of this, whenever any color significantly deviates from the total image average, the graph flattens out except for one vertical spike representing the dominant pixel. This unfortunate behavior makes a basic contrast adjustment an exercise in futility as the white and black indicators spike and the middle values appear to bottom out by comparison. Hopefully this will be fixed in future updates.