Merge node

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This documentation is for version 1.0 of Merge (net.sf.openfx.MergePlugin).

Description

Pixel-by-pixel merge operation between two or more inputs. Input A is first merged with B (or with a black and transparent background if B is not connected), then A2, if connected, is merged with the intermediary result, then A3, etc.

A description of most operators is available in the W3C Compositing and Blending Level 1 Recommendation https://www.w3.org/TR/compositing-1/ and a complete explanation of the Porter-Duff compositing operators can be found in “Compositing Digital Images”, by T. Porter and T. Duff (Proc. SIGGRAPH 1984) http://keithp.com/~keithp/porterduff/p253-porter.pdf

Note that if an input with only RGB components is connected to A or B, its alpha channel is considered to be opaque (one) by default, thus the output will be completely opaque if the checkbox for channel A of input B is checked. One reason for this behaviour is that non-zero RGB values with a zero A value are not valid alpha-premultiplied RGBA values. If the user wishes to keep the background fully transparent, it can only be black, which is equivalent to not using the merge operator. Non-black fully transparent pixels should never appear anywhere in a proper compositing graph.

Operators

The following operators are available.

Porter-Duff compositing operators

  • copy: A (a.k.a. src)
  • over: A+B(1-a) (a.k.a. src-over)
  • under: A(1-b)+B (a.k.a. dst-over)
  • in: Ab (a.k.a. src-in)
  • mask: Ba (a.k.a dst-in)
  • out: A(1-b) (a.k.a. src-out)
  • stencil: B(1-a) (a.k.a. dst-out)
  • atop: Ab + B(1 - a) (a.k.a. src-atop)
  • xor: A(1-b)+B(1-a)

Blend modes, see https://en.wikipedia.org/wiki/Blend_modes

Multiply and Screen
  • multiply: AB, A if A < 0 and B < 0
  • screen: A+B-AB if A or B <= 1, otherwise max(A, B)
  • overlay: multiply(A, 2*B) if B < 0.5, screen(A, 2*B - 1) if B > 0.5
  • hard-light: multiply(2*A, B) if A < 0.5, screen(2*A - 1, B) if A > 0.5
  • soft-light: burn-in if A < 0.5, lighten if A > 0.5
Dodge and burn
  • color-dodge: brighten B towards A
  • color-burn: darken B towards A
  • pinlight: if B >= 0.5 then max(A, 2*B - 1), min(A, B * 2) else
  • difference: abs(A-B) (a.k.a. absminus)
  • exclusion: A+B-2AB
  • divide: A/B, 0 if A < 0 and B < 0
Simple arithmetic blend modes
  • divide: A/B, 0 if A < 0 and B < 0
  • plus: A+B (a.k.a. add)
  • from: B-A (a.k.a. subtract)
  • minus: A-B
  • difference: abs(A-B) (a.k.a. absminus)
  • min: min(A, B) (a.k.a. darken only)
  • max: max(A, B) (a.k.a. lighten only)
Hue, saturation and luminosity
  • hue: SetLum(SetSat(A, Sat(B)), Lum(B))
  • saturation: SetLum(SetSat(B, Sat(A)), Lum(B))
  • color: SetLum(A, Lum(B))
  • luminosity: SetLum(B, Lum(A))

Other

  • average: (A + B) / 2
  • conjoint-over: A + B(1-a)/b, A if a > b
  • disjoint-over: A+B(1-a)/b, A+B if a+b < 1
  • freeze: 1-sqrt(1-A)/B
  • geometric: 2AB/(A+B)
  • grain-extract: B - A + 0.5
  • grain-merge: B + A - 0.5
  • hypot: sqrt(A*A+B*B)
  • matte: Aa + B(1-a) (unpremultiplied over)
  • reflect: A*A / (1 - B)

See also:

Inputs

Input Description Optional
B The main input. This input is passed through when the merge node is disabled. Yes
A The image sequence to merge with input B. Yes
Mask   Yes
A2   Yes

Controls

Parameter / script name Type Default Function
Operation / operation Choice over
The operation used to merge the input A and B images.
The operator formula is applied to each component: A and B represent the input component (Red, Green, Blue, or Alpha) of each input, and a and b represent the alpha channel of each input.
If Alpha masking is checked, the output alpha is computed using a different formula (a+b - a*b).
Alpha masking is always enabled for HSL modes (hue, saturation, color, luminosity).
atop: Ab + B(1 - a) (a.k.a. src-atop)
average: (A + B) / 2
color: SetLum(A, Lum(B))
color-burn: darken B towards A
color-dodge: brighten B towards A
conjoint-over: A + B(1-a)/b, A if a > b
copy: A (a.k.a. src)
difference: abs(A-B) (a.k.a. absminus)
disjoint-over: A+B(1-a)/b, A+B if a+b < 1
divide: A/B, 0 if A < 0 and B < 0
exclusion: A+B-2AB
freeze: 1-sqrt(1-A)/B
from: B-A (a.k.a. subtract)
geometric: 2AB/(A+B)
grain-extract: B - A + 0.5
grain-merge: B + A - 0.5
hard-light: multiply(2*A, B) if A < 0.5, screen(2*A - 1, B) if A > 0.5
hue: SetLum(SetSat(A, Sat(B)), Lum(B))
hypot: sqrt(A*A+B*B)
in: Ab (a.k.a. src-in)
luminosity: SetLum(B, Lum(A))
mask: Ba (a.k.a dst-in)
matte: Aa + B(1-a) (unpremultiplied over)
max: max(A, B) (a.k.a. lighten only)
min: min(A, B) (a.k.a. darken only)
minus: A-B
multiply: AB, A if A < 0 and B < 0
out: A(1-b) (a.k.a. src-out)
over: A+B(1-a) (a.k.a. src-over)
overlay: multiply(A, 2*B) if B < 0.5, screen(A, 2*B - 1) if B > 0.5
pinlight: if B >= 0.5 then max(A, 2*B - 1), min(A, B * 2) else
plus: A+B (a.k.a. add)
reflect: A*A / (1 - B)
saturation: SetLum(SetSat(B, Sat(A)), Lum(B))
screen: A+B-AB if A or B <= 1, otherwise max(A, B)
soft-light: burn-in if A < 0.5, lighten if A > 0.5
stencil: B(1-a) (a.k.a. dst-out)
under: A(1-b)+B (a.k.a. dst-over)
xor: A(1-b)+B(1-a)
Bounding Box / bbox Choice Union
What to use to produce the output image’s bounding box.
Union (union): Union of all connected inputs.
Intersection (intersection): Intersection of all connected inputs.
A (a): Bounding box of input A.
B (b): Bounding box of input B.
Alpha masking / screenAlpha Boolean Off When enabled, the input images are unchanged where the other image has 0 alpha, and the output alpha is set to a+b - a*b. When disabled the alpha channel is processed as any other channel. Option is disabled for operations where it does not apply or makes no difference.
R / AChannelsR Boolean On Use red channel from A input(s).
G / AChannelsG Boolean On Use green channel from A input(s).
B / AChannelsB Boolean On Use blue channel from A input(s).
A / AChannelsA Boolean On Use alpha channel from A input(s).
R / BChannelsR Boolean On Use red channel from B input.
G / BChannelsG Boolean On Use green channel from B input.
B / BChannelsB Boolean On Use blue channel from B input.
A / BChannelsA Boolean On Use alpha channel from B input.
R / OutputChannelsR Boolean On Write red channel to output.
G / OutputChannelsG Boolean On Write green channel to output.
B / OutputChannelsB Boolean On Write blue channel to output.
A / OutputChannelsA Boolean On Write alpha channel to output.
Invert Mask / maskInvert Boolean Off When checked, the effect is fully applied where the mask is 0.
Mix / mix Double 1 Mix factor between the original and the transformed image.