Quantcast Avisynth histogram vs. ColorYUV for calibrating levels? - digitalFAQ Forum
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  #1  
12-27-2015, 01:01 PM
CyborgHyena CyborgHyena is offline
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Which is better for calibrating the levels of a clip in Avisynth, the histogram or ColorYUV(analyze=true)?

Because even if I stretch the luma 245 with ColorYUV, the graph does not enter the brown portion.

I thought the brown parts of the histogram graph are from 0-15 and 236-255?

This is the Avisynth script I used for the attached pictures.

Code:
AviSource("1995.avi")
AssumeTFF()
Crop(8,0,-8,-8) # crop vhs noise and black borders

#ColorYUV(analyze=true)
#ColorYUV(off_y=-6, gain_y=16)

#ColorYUV(analyze=true)

ConvertToYV16(interlaced=true)

histogram(mode="levels")


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File Type: zip pictures.zip (3.95 MB, 9 downloads)
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  #2  
12-27-2015, 04:13 PM
themaster1 themaster1 is offline
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to modify the luma levels i suggest you use the ylevels filter (which is more accurate)
and for the histogram you can use ColorYUV(analyze=true) which display numbers instead of a graph or both at the same time:
ColorYUV(analyze=true)
Histogram("levels")

Brown parts are out of range levels for TV but the more important is to get the blacks right (not too dark) you can have brights out of range... a little
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12-28-2015, 01:48 PM
msgohan msgohan is offline
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Quote:
Originally Posted by CyborgHyena View Post
Because even if I stretch the luma 245 with ColorYUV, the graph does not enter the brown portion.
It does. You have to look very closely to see where it's happening, because it's not many pixels. ColorYUV(analyze=true) will report a maximum value even if only a single stray pixel of noise happens to hit that level.

Histogram_waveform_blownup.png


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12-28-2015, 04:13 PM
CyborgHyena CyborgHyena is offline
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Quote:
Originally Posted by msgohan View Post
It does. You have to look very closely to see where it's happening, because it's not many pixels. ColorYUV(analyze=true) will report a maximum value even if only a single stray pixel of noise happens to hit that level.

Attachment 5645
You're right, now I see it when I zoom in to the graph.

The lowest value in this clip is 9 and the highest 242.

For my future caps I will decrease the contrast and brightness much more, but it's hard to find a scene which has a large range though.
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avisynth, histogram, levels, luma

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