Layer

Layer (aka overlay, blend, merge) merges two clips of possibly different sizes, but with the same color format.

For pixel-wise transparency information, the alpha channel of an RGBA overlay_clip is used as a mask.

Note that some modes can be similar to Overlay, but the two filters are still different.

• Overlay accepts mask clip, Layer would use existing A plane.

• Overlay "blend" is Layer "add", Overlay "add" is different.

• Lighten and darken is a bit different in Overlay.

• Layer has "placement" parameter for proper mask positioning over chroma.

Syntax and Parameters

Layer (clip base_clip, clip overlay_clip, [string "op", int "level", int "x",
       int "y", int "threshold", bool "use_chroma", float "opacity", string "placement"] )

base_clip

the underlying clip which determines the size and all other video and audio properties of the result. YV411 is not supported.

overlay_clip

the clip which is merged onto clip. If RGB32 or other alpha-aware color space, the alpha channel is used as a mask. Non-alpha plane YUV/planar RGB color spaces act as having a fully transparent alpha channel. Color format must match base_clip.

Note: if destination is YUVA/RGBA, the overlay clip also has to be Alpha-aware type. Alpha channel is not updated for YUVA targets, but RGBA targets do get the Alpha updated (like the old RGB32 mode did - compatibility)

op

the performed merge operation, which can be: "add", "subtract", "lighten", "darken", "fast", "mul"

Operation	Example	Description
add		This is the default mode. Equivalent to Overlay(mode="blend") overlay_clip will be copied on top of the original, in proportion to opacity or level and subject to the alpha channel. The difference between base_clip and overlay_clip is multiplied with alpha and added to base_clip. - alpha=0d → only base_clip visible - alpha=128d → base_clip and overlay_clip equally blended - alpha=255d → only overlay_clip visible Formula used : - using opacity parameter - Alpha-aware: base = base + (overlay - base) * opacity * alpha / max_range - No alpha: base = base + (overlay - base) * opacity - Deprecated method using level for 8 bit RGB and YUY2 formats - RGB: base = base + ((overlay - base) * (alpha * level + 1) / 256) / 256 - YUY2: base = base + ((overlay - base) * level) / 256
subtract		base_clip minus overlay_clip. The same as "add", but overlay_clip is inverted before adding. If both clips are equal and opacity = 0.5 (level = 128), a flat gray field is returned compare to Subtract .
lighten		Copy overlay_clip over base_clip in areas where overlay_clip is lighter by threshold. Performs the same operation as "add", but only when overlay_clip is BRIGHTER than base_clip. use_chroma must be true. Also known as lighter color.
darken		Copy overlay_clip over base_clip in areas where overlay_clip is darker by threshold. The same as "lighten", but it is performed only when overlay_clip is DARKER than base_clip. use_chroma must be true. Also known as darker color.
mul		base_clip multiplied by overlay_clip. This will generally make the output darker. - alpha=0d → only base_clip visible. - alpha=255d → approx. the same luminance as base_clip but with the colors of overlay_clip. See GIMP: Multiply
fast		Like "add", but without masking. use_chroma must be true; opacity, level and threshold are not used. The result is simply the average of base_clip and overlay_clip.

level

Note: deprecated in Avisynth+, use "opacity" instead.

Original meaning: the strength of the performed operation.

• 0: the base_clip is returned unchanged,

• 257 (256 for YUY2): the maximal strength is used.

x, y

offset position of the overlay_clip

threshold

Changes the transition point of op = "darken", "lighten.".

Automatically scaled for bit depths over 8, keep it between 0 and 255

use_chroma

Use chroma of the overlay_clip, default=true.

When false only luma is used. Must be true for op = "darken", "lighten", "add."

opacity

Transparency level.

Usable for all bit depths, replaces the previous level parameter.

Similar to "opacity" in "Overlay".

Valid values are 0.0 to 1.0. Default value is 1.0 if level does not exist. (1.0 means full transparency)

If level parameter is given then opacity is calculated as:

• for color spaces having alpha: opacity = level / ((1 << bits_per_pixel) + 1) which gives 1.0 for level=257 (@8bit) and 65537 (@16 bits)

• for color spaces not having alpha: opacity = level / ((1 << bits_per_pixel)) e.g. for YUY2 or other non-Alpha, gives 1.0 for level=256 (@8bit)

"opacity" parameter is bit depth independent (unlike level which was maxed with level=257 when RGB32 but level=256 for YUY2/YUV)

Note: originally level was used in formula: (alpha*level + 1) / range_size, now level is calculated from opacity as: level = opacity * ((1 << bits_per_pixel) + 1)

placement

chroma placement for 420 and 422 YUV formats.

Possible values: "mpeg2" (default), "mpeg1".

Used in "mul", "darken" and "lighten", "add" and "subtract" modes with planar YUV 4:2:0 or 4:2:2 color spaces (not available for YUY2) in order to properly apply luma/overlay mask on U and V chroma channels.

Other notes

Audio, FrameRate and FrameCount are taken from the first clip.

There are some differences in the behaviour and the allowed parameter depending on the color format and the operation; here are the details:

• When there is no mask (alpha channel), the alpha channel is assumed to be fully opaque (255d) everywhere.

• in alpha-aware color spaces alpha channel is multiplied with opacity, so the resulting alpha is

  alpha * opacity

  This means for full strength of operation, alpha has to be 255d and opacity has to be 1.0.

Examples

This can be used to combine two captures of different broadcasts for reducing noise. A discussion of this idea can be found in this thread. A sample script (of course you have to ensure that the frames of the two clips match exactly -- use DeleteFrame if necessary):

clip1 = AviSource("F:\shakira-underneath_your_clothes.avi").ConvertToYUY2
clip2 = AviSource("F:\shakira-
underneath_your_clothes2.avi").ConvertToYUY2
return Layer(clip1, clip2, "fast")

Changelog

Version	Changes
3.5.0	Layer: support RGB24 and RGB48
3.4.0	Layer: support almost all formats, not only RGB32 and YUY2 except RGB24, RGB48, YV411 add "opacity" and "placement" parameters Fix: add proper rounding for add/subtract/lighten/darken Fix: "lighten" and "darken" gave different results between yuy2 and rgb32 when Threshold<>0 Fix: "darken" for RGB32 when Threshold<>0 Fix: "lighten" and "darken" for YUY2 when Threshold<>0

$Date: 2025/01/15 13:15:00 $