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AVX Plug-Ins

User Guide

"Tips" appear in green. Tips will save you time but are not essential information.

"Cautions" appear in red.  Be sure to read and understand this information.

3Prong’s ColorFiX AVX Plug-In provides Avid users with expanded color correction capabilities, including selective or secondary correction, desaturation, true legalizing, and a powerful keying ability. All settings can be varied over time with keyframes.

ColorFiX provides adjustments for both RGB and Y/Cb/Cr color spaces within a single plug-in, giving superior results and more control than a set of individual effects. ColorFiX is optimized to bypass processing in either color space when not required.

ColorFiX has two main paths for image processing: the Main path, and the Select path. Akin to “secondary color correction”, the Select path alters only a selected range of colors. The isolated Select colors are blended back with the result of the Main processing before Legalizing and Output.

Common Controls

Controls are grouped into sections, with Enable buttons at the top right of most groups. In the example image below, the Enable button is purple. For best rendering speed and the cleanest image, disable any groups that you do not need by clicking off the purple Enable button. (As with all Avid effects, groups are enabled or disabled for the entire effect, not by keyframes.)

View changes the video output between the full results of ColorFiX processing (when disabled) and the menu selection:

• Input: simply toggle the Enable button to see the uncorrected Input (menu default). Leave View disabled when performing final rendering. Use View Input rather than the Avid Dual-Split button. Dual-Split shows you the track below instead of the Input.
  
• Select Mask: areas of the image for Select processing are presented as a gray-scale mask. (You may render this view to produce a moving matte or alpha channel for use with another effect.)
  
• Mute Legal: shows acceptable colors as gray scale, leaving any illegal colors visible.

Eyedropper tools: In the Select Old, Black Balance and White Balance groups, there are color pickers used for choosing color directly from the image. Click and hold the mouse button when the pointer is in the current color square (shown in red in the example at right), and it becomes an eyedropper. Drag to the image to pick a color, and release.

(The button to the left of the red square brings up the computer's color picker, but neither this nor directly adjusting the RGB sliders is helpful in picking an existing image color.)

You must pick colors from the unprocessed Input image, not from the already corrected result. There are several ways:

• Use the eyedropper immediately after applying ColorFiX, before you make any other adjustments.
• Temporarily enable the View group to see a view of the Input.
• Temporarily disable every group.
• Sample from the image in the source clip's window (does not work on all Avid systems).
• If your ColorFiX effect is on a filler segment on the track above the clip to be adjusted, you can use the timeline track monitor button to temporarily switch monitoring to the lower track.

In Avid Xpress DV only, an Avid bug may cause inferior results when picking extreme colors (those which are RGB-clipped at 0 or 255). ColorFiX compensates for this as much as possible, but if the sequence is moved from Avid Xpress DV to another type of Avid system, you may get better results by reselecting the colors after recapturing.

Select Path

Use of the Select feature has four steps:

• Select Old: pick samples of the colors to be altered.
• Select Mask: increase the range of colors from the picked samples, and modify the resulting mask.
• Select Crop: crop and feather the mask if desired.
• Select New: adjust the new colors that replace the old.
  

Select Old

Use any or all of the four Select Old color pickers to select the particular colors to be changed from the original image. Each picker can be independently enabled or disabled, and the picked samples are held in that keyframe.

Normally, any object in the scene whose color is to be changed (say, a subject’s blue shirt) will have a range of color values. Use the four pickers to choose the more extreme values from the range of blues to be replaced. For example, you might pick a sample from a lighter part of the shirt, one from a darker part, one from a more saturated part, and a less saturated part. If you want to include all the color values in between those you have picked, make sure the Join button in the Select New group is on.

Though more tricky to set up, you may instead choose up to four completely independent colors for changing (say red, orange, yellow and green from the necktie, all to be desaturated). In this case, because other colors that you don't wish to select will likely lie in between those picked, you will want the Join button off.

You may also choose to Exclude any of the picked colors from the selection. This can help to narrow the range of colors, especially when Join is used.

Select Mask

You may then expand the Range and Tolerance to include other colors.

• Luma Range expands the selection to include more brightness variation.
• Chroma Range expands the selection to include more chroma (hue and saturation) variation.
• Tolerance softens the selection threshold, so that borderline colors do not pop in and out of the selection as they vary slightly with the action. You will always want Tolerance to be set greater than zero.

ColorFiX selects colors in a three-dimensional space but this diagram gives a simple one-dimensional example with arbitrary numbers to show how Range and Tolerance work.

Assume that you use the first Select Old color picker to choose a pixel with a value of 75, and a second picker to pick a pixel with a value of 80. If the Join button is on, the selection expands to all values from 75 through 80.

To include more colors, you expand the Range to 20. Now pixels with values of 55 to 100 would be fully selected.

Lastly, some Tolerance is usually needed to make the Select correction blend well. A Tolerance from 0 to 10 would taper the included range from 110 to 45.

• Invert selects the values that were not chosen, and excludes the values that were chosen.
• Blur is a spatial blur that reduces the sharpness of the mask of selected pixels. Even if neighboring pixels are a completely different color, they are partially included in the selection.
  

Select Crop

This limits the areas of the image that are selected by an adjustable rectangle. First adjust the Top or Bottom Crop slider to open up the on-screen rectangle, and you may then drag the rectangle itself or its corners.

• Feather softens the outside edge of the cropping. Increasing the feathering grows the size of the rectangle.
• Invert includes the selected pixels outside of the rectangle instead of those inside.
  

Select New

The Select New adjustments apply to the entire range of colors selected. This does not mean all the selected colors end up the same. The differences between various original colors are maintained, but each of them is shifted relatively by the Hue, Sat, and Luma controls.

You can preserve original colors in the scene while changing the others in the main path. For example, you could select the color of the lips of a facial close-up in the Select Old tool, yet disable the Select New group, preserving their color from the input image. Meanwhile, in the Main Chroma group you could drop the Saturation to zero, making the rest of the face black and white.

ColorFiX can selectively change colors that have low or no saturation. This feature is rarely available in other secondary color correctors. Moreover, you may also introduce color into these areas, by activating the Colorize button in the Select New group. If the sky is “blown out” white, you may convert those whites to blues. (For more realism in this case, crop just above the horizon and feather the crop.) Colorize removes all the chroma from the Selected areas before a new color vector is applied.

ColorFiX can be used to do a "self" luma key or chroma key by replacing the Selected colors with another image. When the Key Fill button in the Select New group is on, video from the timeline tracks below fills the selected area. Further, that fill video may be adjusted by the Luma, Hue, and Sat controls in the Select New group while the Main path is used to adjust the foreground. With four Select Old pickers, you can key in or key out multiple color or brightness ranges.

This powerful feature allows many creative possibilities. Using the sky example above, you might fill the white sky selection with a sky image with clouds from the track below, and even color-correct both the new sky and the foreground to better match.

Notes on Select Use

Successfully replacing colors in an image is always a challenge, and much more so in video than in stills. Best results come with: 

• a narrow range of colors to be replaced
• good contrast from the other colors in the scene
• new colors close to the old, especially in hue.
• stationary subjects
• little noise or grain
• less compression

It may not be possible to isolate the undesired colors completely without including some of the other ones. Experimentation with the controls is required. Don’t forget to check some other random frames in the clip before rendering. All Select parameters may be keyframed if required.

Main Path

ColorFiX controls appear in the Effect Editor in the general order of processing, from top first to bottom last. For example, the Luma Group is above the Chroma Group, because luma processing occurs before chroma processing. This is also the suggested order for adjusting the controls, because higher adjustments (for example, RGB Gain) could throw out settings that are further down (such as Desat).

A basic technique in color correcting is to fix the overall look of the image first, and then perform the tweaking to get a certain look or add effects. Following the general order of the controls from top to bottom leads to this manner of working. For example, you would usually correct the Luma range and the RGB balances before adjusting the Saturation and Hue.

RGB

• RGB Lifts are offset or black level controls. Master Lift may be used to preserve the relative settings of the RGB controls but adjust them together.
• RGB Gammas, used skillfully, can correct skin tones while preserving white and black balance. A Master Gamma is also provided.
• RGB Gains are provided. The Master Gain control operates like a conventional video gain control, in that saturation gain varies in tandem with the brightness. It is useful to preserve the relative settings of the RGB controls but adjust them together to prevent clipping.
  

Luma

The Luma Group has a variety of controls for varying the brightness of the image. To try out these controls and get a feel for them, use a gray scale as a test image. Avid supplies a test pattern file called “Ramp_1-254” that can be imported (use the “601” color levels) for this purpose. 3Prong's WaveScope plug-in is ideal to view the results, even when unlicensed. Apply WaveScope to filler on the video track above ColorFiX.

• Black is a conventional black level or setup control.
• Inverse Gain is an alternative to the conventional setup or black level control, or the frustrating interaction of brightness and contrast controls. Rather than adding or subtracting a fixed amount to the entire image, Inverse Gain has less effect on brighter parts of the image.
• Black Stretch is a gamma control that only affects the darker parts of the image. Increase it to make dark detail more visible.
• Stretch Range adjusts the brightness level below which Black Stretch is active.
• Gamma adjusts the brightness of the midtones in the image. Increasing Gamma lifts the midtones without changing the blackest and whitest parts of the image. You may also use the Master Gamma in the RGB Gamma group.
• Gain works only on the luma portion of the image. If you drop the Luma Gain control to 0, you will see that there is still chroma present in the output image. If overall brightness adjustment is desired, use the Master Gain control in the RGB Gain group instead, or use Luma Gain in combination with the Saturation control.
• White Knee helps prevent white areas from clipping. If the brightness is boosted by the Gain control to brighten some dark areas, this may push brighter areas above the maximum. Reduce the White Knee setting to compress the white levels to below the clipping point and preserve a bit of detail. (The White Knee slope varies with the White Clip control in the Legalize group.)
• Invert inverts the entire luma curve to negative.
  

Black Balance
White Balance

These features allow you to automatically remove or diminish an overall color cast due to an incorrect camera setting, varying light conditions, film color problems, etc. Simply point to an area of the image that should be color-neutral (white, gray, or black) but is not. ColorFiX detects the vector of the color cast in the sample, and applies an inverse vector to the entire image, subtracting or dividing out the offending color.

White balance is used when the degree of color cast increases with image brightness. Black balance is used when the degree of color cast is constant throughout the luma range.

When using Black Balance or White Balance eyedroppers, ensure that you are picking from the input image.

For a White Balance sample, use the eyedropper tool to choose a part of the image that should be near-white or light gray. Don’t choose the very brightest part of the image, which may be clipped. (Any of the RGB sliders at their limits indicates clipping.)

For a Black Balance sample, use the eyedropper tool to choose a part of the image that should be near-black or dark gray. Don’t choose the very darkest part of the image, which may be clipped.

Bad white balance is a more common problem than black balance, so try that first. If the results are not sufficient, disable the White Balance, and try Black Balance alone. Then try enabling the White Balance again without changing its setting from your first attempt. You may also try a new White Balance sample taken from the Black Balanced output.

Black Balance and White Balance may not remove all sorts of color casts automatically. Rather than trying to adjust the White or Black Balance RGB sliders manually, you may find the Color Difference controls easier to adjust. Observing a vectorscope such as 3Prong's WaveScope can be very helpful in solving a color balance problem. Typical images have amounts of white or black that you can center in the vectorscope display.

Chroma

• Hue rotates all colors in the image around the color spectrum. (Hue uses a similar algorithm to the Avid Color Effect, which tends to distort when hue transformations are extreme.)
• Saturation controls the amount of color, from black and white to highly saturated.
• Invert inverts all the vectors 180 degrees so that each color is replaced with its complement.
  

Style Group

• Posterization reduces the number of luma levels in the image. ColorFiX gives a very fine adjustment to allow gradual introduction of the effect. However, you may find dissolving from the normal image to the ColorFiX-posterized image a more graceful method than keyframing the posterization.
• Solarization sets a threshold for inverting the luma of the image. This Solarization control works a little differently from the one in the Avid Color Effect, in that values beyond 127 continue to darken the brighter parts of the image rather than brightening the dark parts. This allows the darkening quality to be used on scenes that are already fairly dark without turning the image negative.
  

Color Difference

These controls operate on standard digital video components. Cb and Cr can be thought of as the horizontal and vertical directions on the vectorscope. The Offsets shift the chroma up and down or back and forth, and the Gains expand or contract in these dimensions.

When you “can’t get all the dots in the boxes”, these controls will help repair certain kinds of component analog video level errors, and can also help with correcting bad white balance and black balance.

Desaturate

The controls can be used to purify the highest and lowest levels. If needed, Desaturate should be set last, after other corrections have produced the proper color balance and good skin tone. A common use for Desaturate Whites is when color-correcting previously titled footage. After overall color adjustments to color balance the background, titles may no longer be white. Desaturating the highest luma areas can then restore the titles to white.

• Full sets the luma point beyond which there is complete elimination of saturation. Set this first to eliminate most of the color pollution in areas that should be white or black.
• Soft sets the luma point where saturation reduction begins, relative to the Full control. Use of this blending is recommended so that the chroma does not flicker on and off with any subtle luma changes during the scene.
  

Legalize

Color correction or other processes can produce excessive video levels that are a problem in later transmission or distribution. A broadcaster or distributor might reject a program with so-called “illegal” levels on technical grounds. ColorFiX provides a set of controls in the Legalize group to limit excessive video levels, whether caused by ColorFiX or already present in the material.

There is no universal standard, but individual broadcasters will provide delivery specifications including legal levels that they expect program suppliers to meet. In North America, specs usually refer to composite video measurements, so Legalize limits levels with reference to that domain. ColorFiX uses percentage values, not IRE or mV values. To find the percentage setting needed for the controls, look up your desired IRE or mV value in this table, or enter your desired IRE or mV value at the bottom left and press the Convert button.

Chroma Limit sets the maximum peak-to-peak chroma level without regard to luma. ColorFiX reduces saturation as necessary, without changing the hue or luma.

Dark Chroma and Bright Chroma set the upper and lower bounds of the composite video signal. Composite video has a chroma signal “riding” upon the luma waveform. Saturated bright or dark colors may have extreme low or high luma values, together with a lot of chroma. Even if neither luma nor chroma alone is excessive, the combination can be illegal. Yellow and cyan can sometimes be troublesome as bright chroma, and blue as dark chroma. ColorFiX reduces saturation as necessary, without changing the hue or luma.

White Clip sets the maximum luma output. In broadcast digital video, reference white of 100% corresponds to a digital level of 235. White excursions up to 110% (digital level of 255) are technically possible, but individual broadcasters may insist on limiting the peaks to some lower level.

Black Clip sets the minimum luma output. In broadcast digital video, reference black of 0% corresponds to a digital level of 16. Black excursions down to -8% (digital 0) are technically possible, but individual broadcasters may insist on limiting the dips to some higher level. If you use NTSC with setup or pedestal, please refer to the chart above to relate Black Clip percentage to IRE levels.

Legalize does not directly measure the actual composite video output of your Avid system, if it has one. Rather, it accurately models parts of an encoder in software. If and when your video is encoded into composite form, you should see similar results.

Limitations

ColorFiX has some limitations in common with other color-correction software and hardware.

Though ColorFiX has internal accuracy which exceeds the 8-bit input and output of Avid systems, it is still possible to push corrections too far. All digital color correction tends to create “contouring” artefacts in the image similar to posterizing. This becomes a problem when the tiny discrete steps between the original adjacent color or luma levels are amplified enough to become visible. Noisy or detailed images tend to hide this problem, while flat areas of shallow color changes show it readily.

The degree of compression used in Avid editing systems will affect the quality of the results greatly. Use of AVR’s in older Avid systems or DV compression in newer ones produces blocking or patterning artefacts which may be greatly exaggerated by color correction.

3Prong has chosen to preserve the power of all controls as much as possible, but digital color spaces are finite. Avid uses RGB for input to and output from AVX plug-ins, but certain colors in Y/Cb/Cr color space have no equivalent in RGB space. Because of these and similar factors, extreme control settings on wide-ranging material may result in hue shifts or internal clipping. For example, using Colorize with extremely high Saturation settings will produce different hues at the extreme top and bottom of the luma range. If you find this to be a problem, decrease the Select New Saturation, or reduce the Bright or Dark Chroma in the Legalize group.

Due to rendering optimization, it is possible to adjust controls of one type so far out that it is impossible to recover the original image downstream with an opposite adjustment to a similar control. For example, if you increase all three RGB gains to maximum, and then reduce the Luma Gain control, there will likely be clipping within ColorFiX.

Legal Disclaimer: While the ColorFiX plug-in was designed with care to adhere to professional standards, 3Prong makes no warranty as to the accuracy or acceptability of video levels produced by ColorFiX, including any results produced by applying Legalize settings, and assumes no liability whatsoever for the technical rejection of programming which may have been processed by ColorFiX. Users assume complete responsibility for the technical standards of work they produce.

Avid Xpress DV / Xpress Pro

The ColorFiX plug-in will license as ColorFiXDV (at a discounted price) on Avid Xpress DV and Avid Xpress Pro systems. (The version from the trial installer now does this automatically, and a separate download is no longer required.)

Due to the way screen colors are handled in Avid Xpress DV and Avid Xpress Pro, if any of the RGB channels show clipping at 0 or 255 when selecting colors in the Select Old and Black and White Balance groups, those functions will not produce optimum results. If moving sequences with ColorFiX effects from Avid Xpress DV to another type of Avid system, you may wish to reselect the colors from the redigitized footage.

ColorFiX Versions

You can bring sequences with earlier versions of ColorFiX effects forward to any other Avid system which is licensed for ColorFiX. For example, you bring a sequence with a ColorFiX effect created on an ABVB system to a Windows or Mac OS X system with a ColorFiX license, and open and adjust the effect, and render.

However, effects created with recent versions of ColorFiX are not backward-compatible with older versions. In this case, timeline icons will be blank and the effect will not open. If the Avid system supports AVX 1.5, older installations can be upgraded by downloading and re-installing the latest trial version. The Unlocking Code will still be valid. (Users upgrading to OS X will have to re-enter their Unlocking Code.)

ABVB systems are AVX 1.0 and cannot be upgraded. You will not be able to move effects created with this version of ColorFiX to ABVB systems. If required, contact 3Prong for a special ColorFiX downgrade which is backward-compatible with ABVB systems (not available for OS X.)

Also see AVX Limitations in the Common Topics section.

Monitoring

For consistent results from color correction, you must have quality monitoring. A broadcast-grade video monitor is the only type that will yield a true picture. Do not color-correct while looking at a television receiver/monitor or your computer timeline monitor! You will be pushing your video in the wrong directions to compensate for colorimetry differences, bad DC restoration, sky-high consumer white points, flesh-tone circuits, etc.

Component video monitors are a pleasure to look at, but composite can be fine as long as you know the encoder is accurate. For example, beware if you are feeding your monitor from the E-E throughput of a video deck, as your TBC settings are affecting the picture!

Relying on your eyes or bad monitoring can lead you astray when color correcting. A waveform monitor and vectorscope are indispensable to keep you on track. Composite measurements can often be more useful than component ones for seeing the legal limits, and are more familiar. 3Prong's WaveScope plug-in provides many types of composite and component measurement and is the ideal companion to ColorFiX.

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