FixLuminance

Warning

This filter is considered broken/deprecated: see discussion

The purpose of this filter is to progressively darken the top of the image; for example, to compensate for certain VCRs which make the top of each frame brighter than the bottom. In practice it only works for NTSC content and it needs its fields separated.

When applying it to an image with height > 255 pixels, you will see a repetitive gradient. So it doesn't work for field-separated PAL content.

Syntax and Parameters

FixLuminance (clip, int intercept, int slope)

clip

Source clip; only YUY2 is supported.

intercept

Bottom line at which to start correction. intercept should be equal to or smaller than the height of the image.

slope

Slope of correction function. The top of the picture is made darker by 1 (on a 0-255 scale) every slope lines.

Maximum darkening (at top line) = intercept / slope

Examples

• Progressively darken top lines:

ColorBars(width=512, height=480, pixel_type="YUY2")
Crop(0, 0, 0, 256)
FixLuminance(100, 4)

Line 99 is normal; line 0, the topmost line, is darker by 25 (intercept/slope = 100/4 = 25)

• Make a ramp test image:

BlankClip(width=512, height=256, pixel_type="YUY2", color_yuv=$FF8080)
FixLuminance(255, 1)

$Date: 2022/02/08 22:44:06 $