Alt scale

Alt scale is a mpv shader. A 2 pass scaler, an alternative to mpv's built in scaling.

Chroma folder contains shaders for upscaling chroma only
Luma folder contains shaders for upscaling and downscaling luma only

altUpscale is optimised for and only does upscaling
altUpscaleUnsharp is optimised for and only does upscaling, also provides unsharp mask
altUpscaleHDR is optimised for and only does upscaling; HDR version
altUpscaleUnsharpHDR is optimised for and only does upscaling, also provides unsharp mask; HDR version
altDownscale is optimised for and only does downscaling
altDownscaleUnsharp is optimised for and only does downscaling, also provides unsharp mask
altDownscaleGaussian is optimised for and only does downscaling, also provides gaussian blur
altDownscaleGaussianUnsharp is optimised for and only does downscaling, also provides gaussian blur and unsharp mask

Usage

• If you place this shader in the same folder as your mpv.conf, you can use it with glsl-shaders-append="~~/FILE_NAME". For an example glsl-shaders-append="~~/altUpscale.glsl".
• Requires vo=gpu-next.
• Note that defualt settings are "simbolic" only, should change them to your liking.
• Note that all downscale shaders can be used for both SDR and HDR content.
• Note that HDR versions are just gamma light so you can use them for SDR

Settings

For better understanding of these settings see research https://github.com/garamond13/Finding-the-best-methods-for-image-scaling
For finding the best parameters you can use BestScalingParamsFinder

Kernel function (K)

Which kernel function to use for calculation of kernel weights. See "KERNEL functions LIST" inside the shader for available kernel functions.

Kernel radius (R)

Kernel radius determines the kernel size, which is ceil(2 * kernel radius) when upsampling (upscale) or ceil(2 * kernel radius * downscale ratio * antialiasing amount) when downsampling (downscale).

Kernel blur (B)

Effectively values smaller than 1 sharpen the kernel and values larger than 1 blur the kernel, 1 is neutral or no effect. Only affects widowed sinc kernels.

Antiringing (AR) (Only for upscale)

Reduces ringing artifacts.

Antialiasing (AA) (Only for downscale)

Effectively trades between aliasing and ringing artifacts. The default value is 1.0.

Kernel functions parameters (P1) and (P2)

Some kernel functions take additional parameters, they are set here.
COSINE (Power of Cosine) - https://en.wikipedia.org/wiki/Window_function#Power-of-sine/cosine_windows
n = P1
Has to be satisfied: n >= 0
n = 0: Box window
n = 1: Cosine window
n = 2: Hann window
GARAMOND (Power of Garamond) - https://github.com/garamond13/power-of-garamond-window
n = P1, m = P2
Has to be satisfied: n >= 0, m >= 0
n = 0: Box window
m = 0: Box window
n -> inf, m <= 1: Box window
m = 1: Garamond window
n = 1, m = 1: Linear window
n = 2, m = 1: Welch window
BLACKMAN (Power of Blackman)- https://github.com/garamond13/power-of-blackman
a = P1, n = P2
Has to be satisfied: n >= 0
Has to be satisfied: if n != 1, a <= 0.16
n = 0: Box window
n = 1: Blackman window
a = 0, n = 1: Hann window
a = 0, n = 0.5: Cosine window
GNW (Generalized Normal Window) - https://ieeexplore.ieee.org/document/6638833
s = P1, n = P2
Has to be satisfied: s != 0, n >= 0
n -> inf: Box window
n = 2: Gaussian window
SAID - https://www.hpl.hp.com/techreports/2007/HPL-2007-179.pdf
eta = P1, chi = P2
Has to be satisfied: eta != 2
FSR (Modified FSR kernel, based on https://github.com/GPUOpen-Effects/FidelityFX-FSR) - for referernce see the research above
b = P1, c = P2
Has to be satisfied: b != 0, b != 2, c != 0
c = 1: FSR kernel
BCSPLINE - https://www.cs.utexas.edu/~fussell/courses/cs384g-fall2013/lectures/mitchell/Mitchell.pdf
B = P1, C = P2
Keys kernels: B + 2C = 1
B = 1, C = 0: Spline kernel
B = 0, C = 0: Hermite kernel
B = 0, C = 0.5: Catmull-Rom kernel
B = 1 / 3, C = 1 / 3: Mitchell kernel
B = 12 / (19 + 9 * sqrt(2)), C = 113 / (58 + 216 * sqrt(2)): Robidoux kernel
B = 6 / (13 + 7 * sqrt(2)), C = 7 / (2 + 12 * sqrt(2)): RobidouxSharp kernel
B = (9 - 3 * sqrt(2)) / 7, C = 0.1601886205085204: RobidouxSoft kernel

Sigmoidal curve settings (C) and (M) (Only for upscale and not part of HDR versions)

Contrast C is equivalent to mpv's --sigmoid-slope and midpoint M is equivalent to mpv's --sigmoid-center.

Gaussian blur and unsharp mask (Only for gaussian and unsharp versions)

• Unsharp mask works like this: sharpened = original + (original − blurred) * amount.
• Blur kernel radius is independent from scaling kernel radius.
• For shaders with both unsharp mask and gaussian blur all settings are independent.

Blur spread or amount (S)

Gaussian blur sigma value, controls the blur intensity and how much it will be spread accros the blur kernel.

Blur kernel radius (R)

Determines how many neighboring pixels will contribute to the blurred value of the center pixel inside the blur kernel.

Sharpening amount (A) (Only for unsharp versions)

Sharpening amount or strenght.