Overlay

Overlay(clip clip, clip overlay [, int x, int y, clip mask, float opacity, string mode, bool greymask, string output, bool ignore_conditional, bool pc_range])

Overlay puts two clips on top of each other with an optional displacement of the overlaying image, and using different overlay methods. Furthermore opacity can be adjusted for the overlay clip.

Input for overlay is any colorspace, and colorspaces of different clip doesn't matter! The input clips are internally converted to a general YUV (with no chroma subsampling) format, so it is possible for the filter to output another colorspace than the input. It is also possible to input video in different colorspaces, as they will be converted seamlessly. It is however not recommended to use overlay only for colorspace conversions, as it is both slower and with slightly worse quality.

In general all clips are treated as 0->255 values. This means that numbers will not be clipped at CCIR-601 range. Use Limiter for this task afterwards. Masks should also have values from 0->255. You can use Histogram in Histogram("levels") mode to view the color distributions. If your mask is in CCIR-601 range, use ColorYUV(levels="TV->PC") to upscale the color levels.

It is not recommended to do overlays on interlaced material, unless you know what you are doing.

mask This will be used as the transparency mask for the overlay image. The mask must be the same size as the overlay clip. By default only the greyscale (luma) components are used from the image. The darker the image is, the more transparent will the overlay image be. There is no default, but not specifying is equivalent to supplying a 255 clip.

opacity This will set how transparent your image will be. The value is from 0.0 to 1.0, where 0.0 is transparent and 1.0 is fully opaque (if no mask is used). When used together with a mask this value is multiplied by the mask value to form the final opacity. Default value is 1.0

mode Mode defines how your clip should be overlaid on your image.

Mode	Description
Blend	This is the default mode. When opacity is 1.0 and there is no mask the overlay image will be copied on top of the original. Ordinary transparent blending is used otherwise.
Add	This will add the overlay video to the base video, making the video brighter. To make this as comparable to RGB, overbright luma areas are influencing chroma and making them more white.
Subtract	The opposite of Add. This will make the areas darker.
Multiply	This will also darken the image, but it works different than subtract.
Chroma	This will only overlay the color information of the overlay clip on to the base image.
Luma	This will only overlay the luminosity information of the overlay clip on to the base image.
Lighten	This will copy the light infomation from the overlay clip to the base clip, only if the overlay is lighter than the base image.
Darken	This will copy the light infomation from the overlay clip to the base clip, only if the overlay is darker than the base image.
SoftLight	This will lighten or darken the base clip, based on the light level of the overlay clip. If the overlay is darker than luma = 128, the base image will be darker. If the overlay is lighter than luma=128, the base image will be lighter. This is useful for adding shadows to an image. Painting with pure black or white produces a distinctly darker or lighter area but does not result in pure black or white.
HardLight	This will lighten or darken the base clip, based on the light level of the overlay clip. If the overlay is darker than luma = 128, the base image will be darker. If the overlay is lighter than luma=128, the base image will be lighter. This is useful for adding shadows to an image. Painting with pure black or white results in pure black or white.
Difference	This will display the difference between the clip and the overlay. Note that like Subtract a difference of zero is displayed as grey, but with luma=128 instead of 126. If you want the pure difference, use mode="Subtract" or add ColorYUV(off_y=-128).
Exclusion	This will invert the image based on the luminosity of the overlay image. Blending with white inverts the base color values; blending with black produces no change.

Default value is Blend

greymask This option specifies whether chroma from the mask should be used for chroma transparency. For general purpose this mode shouldn't be disabled. External filters like mSharpen and Masktools are able to export proper chroma maps. Default value is true

output It is possible to make Overlay return another colorspace. Possible output colorspaces are "YV24", "YUY2", "YV12", "Y8", "RGB32" and "RGB24". Default is input colorpace

ignore_conditional This will make Overlay ignore any given conditional variables. See the "Conditional Variables" section for an overview over conditional variables. Default: false

pc_range When set to true, this will make all internal RGB -> YUV -> RGB conversions assume that luma range is 0 to 255 instead of default 16->235 range. It is only recommended to change this setting if you know what you are doing. See the section on "RGB considerations" below. Default: false

RGB considerations

This section will describe things that may give you an explanation of why Overlay behaves like it does when it is given one or more RGB sources. One or more inputs for Overlay are allowed to be RGB-data. However, as Overlay is processing material in the YUV colorspace this will lead to an RGB to YUV conversion. There are two modes for this conversion, toggled by the "pc_range" parameter. This parameter will extend the YUV range from 16-235 (this is the range used by all avisynth converters) to 0-255. There are some cases where enabling pc_range is a good idea:

When overlaying an RGB-clip using the "add", "subtract" or "multiply" modes, the range of the overlay clip is better, if it is 0-255, since this will enable completely dark areas not to influence the result (instead of adding 16 to every value).
When NOT doing a colorspace conversion on output. If the output colorspace (RGB vs. YUV) is different from the input, the scale will be wrong. If pc_range is true, and input is RGB, while output is YUY2 - the YUY2 will have an invalid range, and not CCIR-601 range.

Outputting RGB

It might be a good idea to let Overlay output YUY2, even if your input colorspace is RGB, as this avoids a colorspace conversion back to RGB from YUV. You should however be aware that your material might be "overscaled", as mentioned above, if you use pc_range = true. You can correct this by using ColorYUV(levels="pc->tv") to convert back to 16-235 range.

Inputting RGB for mask clip

The mask clip from RGB may behave a bit different than it could be expected. If you always use a greyscale mask, and don't disable greymask you will get the result you'd expect. You should note that mask clip values are never scaled, so it will automatically be in 0->255 range, directly copied from the RGB values.

Using RGB32 alpha channel

Overlay will never use the alpha channel given in an RGB32 clip. If you want to extract the alpha channel from an RGB32 clip you can use the ShowAlpha command (for example, use Overlay(kitten, 10, 10, kitten.ShowAlpha()) ) to extract the alpha information. For maintaining maximum quality it is recommended to extract the alpha as RGB.

Repeated overlays on RGB base clip

When doing repeated partial overlays on an RGB base clip, the unchanged parts of the base clip will undergo a RGB-YUV-RGB conversion for each call to Overlay, producing a progressive loss of color accuracy. For example, grey colors will acquire a yellowish tinge. In these situations, it is better to convert the base clip to YUY2 in the script before doing the overlays and convert back to RGB afterwards.

Conditional Variables

The global variables "OL_opacity_offset", "OL_x_offset" and "OL_y_offset" are read each frame, and applied. It is possible to modify these variables using FrameEvaluate. The values of these variables will be added to the original on each frame. So if you specify "x = 100" as a filter parameter, and the global variable "ol_x_offset" is set to 50, the overlay will be placed at x = 150.

If you are using multiple filters this can be disabled by using the "ignore_conditional = true" parameter.

There is an example of conditional modification at the ConditionalReader page.

Examples

# Prepares some sources.
bg = colorbars(512,384).converttoyuy2()
text = blankclip(bg).subtitle("Colorbars", size=92, 
\          text_color=$ffffff).coloryuv(levels="tv->pc")

# This will overlay the text in three different versions.
Overlay(bg, text, x=50, y=20, mode="subtract", opacity=0.25)
Overlay(text, x=50, y=120, mode="add", opacity=0.5)
Overlay(text, x=50, y=240, mode="blend", opacity=0.7)

# This will overlay yuy2clip with rgbclip using a yuy2-mask
# (note that the luma range of the mask is [0-255]). 
Overlay(yuy2clip, rgbclip, mask = rgbclip.ShowAlpha("yuy2"))

# which is the same as 
mask = rgbclip.ShowAlpha("rgb").ConvertToYUY2.
\                     ColorYUV(levels="TV->PC")
Overlay(yuy2clip, rgbclip, mask)

# which is the same as 
mask = rgbclip.ShowAlpha("rgb")
Overlay(yuy2clip, rgbclip, mask)

This will take the average of two clips. It can be used for example to combine two captures of different broadcastings for reducing noise. A discussion of this idea can be found here. A sample script (of course you have to ensure that the frames of the two clips matches exactly, use DeleteFrame if necessary):

clip1 = AviSource("F:\shakira-underneath_your_clothes.avi")
clip2 = AviSource("F:\shakira-underneath_your_clothes2.avi")
Overlay(clip1, clip2, mode="blend", opacity=0.5)

Another use is to detect an altered video using Video Error Level Analysis (VELA), where clip2 is clip1 resaved using a h.263 CoDec (e.g. XVID). This method is effective when the suspected altered video (clip1) has not been resaved multiple times. Levels aids in detection view-ability:

clip1 = AviSource("SuspectVideo.avi")
clip2 = AviSource("SuspectVideo_resaved.avi")
result= Overlay(clip1,clip2,mode="Subtract").Levels(0,5,100,0,255)

Use a blue (or any other color) background (blue.jpg is a blue frame overlayed with subtitles in a black rectangle) as mask. The black rectangle containing the subtitles will be visible on the source clip (which is ColorBars here):

testcard = ColorBars()

# get a blue mask clip (the same blue as in ColorBars is used: R16 G16 B180)
maskclip = BlankClip(testcard, color=$0f0fb4)

# Example subtitle file with blue backgroud as above
subs = ImageSource("F:\TestClips\blue.jpg").ConvertToRGB32

maskclip = ColorKeyMask(subs, $0f0fb4, 60)

Overlay(testcard, subs, mask=ShowAlpha(maskclip), mode="blend", opacity=1)

A tolerance of 60 is used here because the blue is not entirely uniform. Near the black rectangles the blue is given by R23 G22 B124. Probably due to the compression of blue.jpg.

Move a red (or any other color) dot on a clip using ConditionalReader (dot.bmp is a red dot on a black background):

a1 = ColorBars().Trim(0,399)
a2 = ImageSource("F:\TestClips\dot.bmp").ConvertToRGB32

# a2.GreyScale returns a grey dot on a black background;
# Levels makes the dot white
mask_clip = Mask(a2, a2.GreyScale.Levels(0, 1, 75, 0, 255))
Overlay(a1, a2, mask=ShowAlpha(mask_clip), y=0, x=0,
\                              mode="blend", opacity=1)

ConditionalReader("xoffset.txt", "ol_x_offset", false)
ConditionalReader("yoffset.txt", "ol_y_offset", false)

Make xoffset.txt containing the x-positions and yoffset.txt containing the y-positions of the moving dot (see ConditionalReader for more info), and put it in the same folder as your script:

xoffset.txt:

Type int
Default -50

R 0 100 20
I 100 200 20 250
R 200 300 250
I 300 400 250 400

yoffset.txt:

Type int
Default -50
 
R 0 100 20
I 100 200 20 350
R 200 300 350
I 300 400 350 40

The figures:

thus the dot moves in the following way: (20,20) -> (250,350) -> (400,40). Nb, it's also possible to do this with Animate.

Changelog:

v2.6	Added output="Y8","YV24"; input: "Y8", "YV16" and "YV24".
v2.55	mode="Multiply" functionality has changed, so it works as it supposed to do.
v2.54	Initial Release.

Overlay

Contents

Parameters

RGB considerations

Outputting RGB

Inputting RGB for mask clip

Using RGB32 alpha channel

Repeated overlays on RGB base clip

Conditional Variables

Examples

Views

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