Premiere Elements 4 through the current version (13/13.1) each have "Alpha Adjust" as a choice under its keying video effects. Never noticed it before. Then a Premiere Elements Mac user asked about "Alpha Adjust" as an alternative to Videomerge for green screen project. Premiere Elements Mac does not have the keying video effects of Green Screen Key, Blue Screen Key, and ChromaKey as does Premiere Elements Windows. And, so far the best alternative for Videomerge in Premiere Elements Mac has been found by many to be Difference Matte.
Alpha Adjust turns out to be an alternative for setting the Opacity that is found in Properties Palette (version 10 and earlier) or Applied Effects Palette (version 11 and later). The Opacity found in either Properties Palette or Applied Effects Palette locations is referred to as a "Fixed Effect".**
Opacity applied as Opacity in Applied Effects Palette "Fixed Effect", See Figure 1.
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| Figure 1. Clip Opacity Applied Using Applied Effects Palette/Opacity Panel Expanded In Premiere Elements 13/13.1. |
Opacity applied using Alpha Adjust keying video effect, See Figure 2
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| Figure 2. Alpha Adjust For Opacity Application To Clip In Premiere Elements 13/13.1 Fx Effects/Keying/Alpha Adjust. |
ISSUE
What is supposed to be gained using Opacity applied using the keying video effect named Alpha Adjust versus Opacity applied from Properties Palette or Applied Effect Palette?
SOLUTION
Which Opacity to use depends on the rendering order wanted in Timeline or export.
The key points for deciding which Opacity to use....
- Rendering order (apparently in Timeline and in export) affects how opacity interacts with visual effects where the alpha channel indicates transparency
- The rendering order goes Video Effects first, the default panel options in Properties Palette or Applied Effects Palette next, and then alpha channel adjustments. And, there is a top to bottom ordering of the list in each of the these categories.
- According to this rendering order, Alpha Adjust/Opacity from fx Effects/Keying would be done before Opacity from Properties Palette or Applied Effects Palette.
- The Adobe recommendation is "If you want opacity to render earlier
or later than certain effects, or if you want to control additional
opacity options, apply the Alpha Adjust video effect".
COMMENTARY
To answer the Premiere Elements Mac user's question about using Alpha Adjust for green screen effect.....No way is seen to use Alpha Adjust as a color key replacement for any of the program's green screening tools, such as ChromaKey, Green Screen Key, Difference Matte, or even Videomerge. However, Adobe writes
Alpha channel‑based keying effect
The Alpha Adjust Key effect lets you invert or turn off a clip’s alpha channel or convert areas without transparency to a mask.But, that is all for clip once it has an alpha channel (transparency). The imported green screen video does not until color-based keying effect is applied to the clip.
Example....
Given clip with purple snow flake image on a solid green background. There is no transparency in that clip. If the clip is on the higher track, the whole image on this clip will be the only one seen.
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| Figure 3. Purple Snow Flake On Solid Green Background. |
If the Alpha Adjust is applied to the clip in Figure 3, there is no way for Alpha Adjust to convert selectively the green to transparency leaving just the purple snow flake on a transparent background. However, the whole clip can be taken to total transparency by moving the Alpha Adjust Opacity slider to 0%.
If instead Green Screen Key is applied to the clip in Figure 3, the green color can be converted to transparency (represented by black) leaving just the purple snow flake. See Figure 4.
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| Figure 4. Green Screen Key Applied To Clip Shown In Figure 3. |
When a plant background image is placed on a track directly below that of this purple snow flake surrounded by transparency, the image below will show through that transparent area in clip on the upper track and be seen.
Now, if the Alpha Adjust is applied to the clip which has had its green replaced with transparency using the Green Screen Key, the opportunity is gained to interpret the alpha channel (transparency where green color was) in the clip using the Alpha Adjust controls of Ignore Alpha, Invert Alpha, Mask Only.
Consider the example of this purple snow flake on its transparent background (from Green Screen Keying) on Video Track 2, and plant background image on Video Track 1. The following shows the effects of changing the Alpha Adjust controls at a fixed Alpha Adjust Opacity setting.
Alpha Adjust Opacity 100%, Ignore Alpha, Invert Alpha, and Mask Only options each Disabled.
Alpha Adjust Opacity 100%, Only "Ignore Alpha" Enabled
Alpha Adjust Opacity 100%, Only "Invert Alpha" Enabled
Alpha Adjust Opacity 100%, Only "Mask Only" Enabled
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*An offshoot of this study was going over the ways to export a Timeline content with transparency and maintain that transparency in the export. The following expands on our previous writings on this matter in the more recent versions of Premiere Elements.
An Example Given For Premiere Elements 13/13.1
Publish+Share
Computer
QuickTime
and under the Advanced Button/Video Tab of the preset selected, the essentials are:
Video Codec = Animation or PNG
No check mark next to Render at Maximum Depth
Depth = 32 bit
Publish+Share
Computer
AVI
and under the Advanced Button/Video Tab of the preset selected, the essentials are:
Video Codec = None
No check mark next to Render at Maximum Depth
Depth = 32 bit
**"Fixed Effect" details can be found in the Adobe document "Adobe Premiere Elements Help/Effects Basics".
ATR
