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Dave's Alpha Control

Disciplines > Photography > Affinity Photo > Resources > Dave's Alpha Control

Download | Discussion | Alpha Squeeze'n'Stretch | Full Alpha Selection | Erase Wt/Gy/Bk Paper | Flatten Alpha | Alpha Map | Alpha to White | Alpha to Black | Alpha to Red | See Also

Download

Click here to download the latest 'Dave's Alpha Control' macro set.

To insert this into your library, simply click on the 3-line 'hamburger' on the top right of the library panel, click on 'Import Macros...' and point it at the downloaded file. Then click on the layer for which you want a model and click once on the appropriate macro in the 'Dave's Alpha Control' library group category.

Discussion

'Alpha' is the same as transparency or opacity, and is also related to masks and selection. Every pixel is described with RGBA values, where RGB is the familiar Red, Green and Blue, while the A stands for Alpha. This means any pixel may be opaque, transparent or partially transparent. In an 8 bit system, where RGB values can each can have 256 different values, so also can the Alpha value of that pixel.

When doing selection, the 'selection' is actually an indication of the alpha value selected, including when you select with a soft brush, you feather the selection or do a Refine. The resultant partially selected pixels are helpful for blending in a selected and adjusted area, but may extend too far. A typical example is in selecting hair, where you get unwanted parts of the background along with the hair.

The macros in this group are intended to help with such editing problems, where pixel alpha may be less than 100%. In particular, they are useful for one of:

• A selection which is placed on a new layer typically with cut/paste.
• A layer which has been masked.
• A layer where the Erase Brush tool has been used to 'paint away' pixels.
• The result of one of the 'Dave's' selection macros.

Note: To be able to see the transparency of pixels, either ensure that Document/Transparent Background is checked, or add a temporary Fill Layer below, set with a contrasting colour (such as magenta).

Alpha Squeeze'n'Stretch

Description

This macro is to help increase or decrease alpha of partially transparent pixels, effectively shifting the perceived boundaries of the layer.

To use it, double-click the Procedural Texture adjustment that appears at the top of the layer stack and adjust the controls as below.

Controls

• Amount: Squeeze -- Stretch: Increase/decrease alpha of partially transparent pixels.
  • Stretch: Any partially transparent pixel is increasingly made less transparent.
  • Squeeze: Any partially transparent pixel is increasingly made more transparent.
• Remove: Mono -- Colour: Decrease alpha of partially transparent pixels that are identified as Mono or Colour.
  • Mono: Any partially transparent pixel identified as Mono by the 'Split Mono – Colour' control is increasingly made less transparent.
  • Colour: Any partially transparent pixel identified as Colour by the 'Split Mono – Colour' control is increasingly made less transparent.
• Split Mono -- Colour: Defines the boundary between Mono and Colour for the 'Remove: Mono – Colour' control above.
  • Mono: Moving the slider left decreases the area that is 'Mono' and increases the area that is 'Colour'.
  • Colour: Moving the slider left decreases the area that is 'Colour' and increases the area that is 'Mono'.

Discussion

The general principle of this macro is to adjust alpha of partially transparent pixels (value greater than 0 and less than 1). An example of its use is after hair selection and 'refine', to remove unwanted extra pixels.

The Mono/Colour removal is an extra tool that may be useful where unwanted edge pixels are dark or light (for example caused by sharpening).

Full Alpha Selection

This allows for the selection of pixels with alpha values within a defined range, including fully transparent or opaque.

Description

This creates a new layer with the visible image, then adds a Procedural Texture child adjustment layer.

To use this, hide the layers below the added layers, then double click the Procedural Texture layer and adjust the controls as below. The best approach is to first turn off layers beneath, then set the first four controls to create the selected area. Then apply other adjustments to suit.

Controls

• Translucent Zero: Minimum alpha value for selection, below which nothing is selected.
  • The zone between Translucent Zero and Translucent Full is a feathered zone, going from zero alpha to full alpha.
• Translucent Full: Minimum alpha value for full selection.
• Opaque Full: Maximum alpha value for full selection.
  • When Opaque Full is at the maximum, pixels that are opaque remain so.
  • Pixels between Opaque Full and Zero have feathered alpha.
• Opaque Zero: Maximum alpha value for zero selection.
• Feather: 0=Lin; 1=Exp; 2=Cos: Adjusts the rate of transition between opaque and transparent pixels.
  • 0: Linear transition.
  • 1: S-curve transition, based on exponential algorithm.
  • 2: S-curve transition, based on cosine algorithm (steeper transition than exponential).
• Invert: 0=No; 1=Yes: Inverts the opacity, so transparent pixels become opaque and vice versa.
• Mono Protect: Selects near-monochrome (and increasingly non-so) to exclude from the selection.
  • Note: Full monochrome happens where R, G and B are all of equal value. Moving the slider right allows for increasing max-min range within R, G and B differences.
• MP Feathering: Feathering from the maximum Mono Protect value back to full Monochrome.
• MP Feathering calculation: MP Fea: 0=Lin; 1=Exp; 2=Cos
  • 0=Lin: Linear feathering, steadily fading from edge
  • 1=Exp: Exponential sigmoid feathering, s-shaped fade
  • 2=Cos: Cosine sigmoid feathering, different s-shaped fade
• MP Mono calculation: Cal: 0=All; 1=Gy; 2=Wt; 3=Bk
  • 0=All: Selects most pixels based on simple 'max-min' algorithm.
  • 1=Gy (default): Selects more greys, based on HSL hue algorithm, avoiding selection of whites/tints and blacks/shades.
  • 2=Wt: Selects greys and whites/tints, based on '(max-min)/max' algorithm.
  • 3=Bk: Selects greys and blacks/shades, based on '(max-min)/(1-min)' algorithm.
• MP Invert: 0=No; 1=Yes
  • 0: Normal selection
  • 1: Invert (select everything that is not selected in Normal condition)

Discussion

This macro is based on other Dave's Selection macros such as found in Luminosity and Hue selection, where a zone with feathered edges is set up for selection, then other controls may be applied, such as changing the feathering algorithm or inverting the selection. The Mono Protect feature works as in other macros, preventing lower saturation pixels from being selected. This is helpful when you want to keep tones and select colours. To reverse this, you can select the MP Invert control.

Erase Wt/Gy/Bk Paper

This is an extension of the 'Erase White Paper' filter, giving dynamic control, Black/Grey erasing and selection inversion.

Description

This works by reducing alpha in white/grey/black with individual controls for each. Note that grey erase works from mid-grey outwards.

While the White/Grey/Black controls can be used together, the basic intent is that only one is used at a time.

The Erase/Invert switch allows you to turn from an erase into a selection, simply by inverting the alpha value.

Controls

Note that the White, Grey and Black controls have a snap point half way up. This may provide a convenient basic value. From zero, nudge a minimum amount to erase pure white/mid-grey/pure black.

• White: Fully left, nothing is erased. Fully right, light colours containing some white are also erased.
• Grey: Fully left, nothing is erased. Fully right, most pixels containing some grey are also erased. Note this starts from mid-grey and expands outwards to darker and lighter greys.
• Black: Fully left, nothing is erased. Fully right, dark colours containing some black are also erased.
• Erase=0; 1=Invert/Select:
  • 0: Default. Erase white/grey/back.
  • 1: Inverts selection, giving a way to select whites/greys/blacks rather than erasing them.

Discussion

The algorithms used work on the principle of combining lightness, as determined by minimum and maximum RGB values and how monochrome the pixel, as determined by the difference between the maximum and the minimum RGB values.

Pixels with 'White' in have a minimum value greater than zero. Pixels with black in have a maximum value less than 100%. Pixels with grey in have both minimum value greater than zero and maximum value less than 100%.

The sliders have a 'snap point' mid-way as the algorithm changes here.

The controls are non-linear in order to give a very wide span of control.

Flatten Alpha

This macro simply ensures all pixels are opaque, removing any feathering.

Description

This works simply by bumping up the alpha value of all pixels to 100%, so each pixel is opaque.

Any pixels which have no information in them, such as those which have been erased, appear as black.

Discussion

This macro can be used to 'unfeather' images, restoring 'faded' areas. It will also show where there is no useful information in the image.

Alpha Map

This macro simply turns all opaque pixels white, all transparent pixels black, and partially transparent pixels to shades of grey.

Description

The macro works by creating a new image from the visible pixels and then turning this into a greyscale map of opacity.

A simple use of this is to identify where pixels are transparent, partially transparent or opaque. The map may also be converted into a mask for selective treatment.

Alpha to White

This macro converts all transparent and partially transparent pixels to white.

Description

This effectively sets all pixels to opaque, removing transparency. This is useful for such as subsequent blending or printing (for example where you have a partially transparent border which you want to print in white.

Discussion

Partially transparent pixels appear as more white than their original colour. This allows for deliberate fading to white.

The macro is very similar to the Alpha to Black and Alpha to Red macros.

Alpha to Black

This macro converts all transparent and partially transparent pixels to black.

Description

This effectively sets all pixels to opaque, removing transparency. This is useful for such as subsequent blending or printing (for example where you have a partially transparent border which you want to print in black.

Discussion

Partially transparent pixels appear as more black than their original colour. This allows for deliberate fading to black.

The macro is very similar to the Alpha to White and Alpha to Red macros.

Alpha to Red

This macro converts all transparent and partially transparent pixels to red.

Description

This effectively sets all pixels to opaque, removing transparency. This is done as a way to make partially transparent pixels more visible, in the same manner as used in the Quick Mask and in selection Refine.

Discussion

Partially transparent pixels appear as more red than their original colour.

The macro is very similar to the Alpha to White and Alpha to Black macros.

See also

If you are having problems downloading the macros, click here to download as zip file.