Welcome to Doom9's Forum, THE in-place to be for everyone interested in DVD conversion.

Before you start posting please read the forum rules. By posting to this forum you agree to abide by the rules.

 

Go Back   Doom9's Forum > Capturing and Editing Video > Avisynth Usage

Reply
 
Thread Tools Search this Thread Display Modes
Old 27th June 2014, 22:40   #1  |  Link
j7n
Registered User
 
j7n's Avatar
 
Join Date: Apr 2006
Posts: 80
Understanding Levels in Firesledge's Dither

I am using Dither 1.19.0 and AviSynth 2.5.8 to downscale, deband and add dither noise to videos. I got Dither from here a long time ago, and have been happy with the results.

However, I am still using basic Levels() from AviSynth, even though I realize increased precision would be needed for this task more than anywhere else. I find the level adjustment in Dither difficult to understand.

The documentation mentions working with curves and converting sample range between TV and PC. So the plug-in is most certainly capable of basic level adjustment.

The docs mention "lut", which I understand stands for look-up table, as well as "reverse polish notation". These terms appear rather intimidating.

I'd like to insert level adjustment, while the picture is still in 16-bits, and avoid installing any new plug-ins to prevent conflicts with my existing stuff.

Could someone please give me a few examples of shifting the histogram up or down, or multiplying it to stretch it? No linear light, or gamma, or anything like that, yet.
j7n is offline   Reply With Quote
Old 28th June 2014, 06:41   #2  |  Link
colours
Registered User
 
colours's Avatar
 
Join Date: Mar 2014
Posts: 312
RPN is not actually as intimidating as it may sound. Instead of writing a mathematical operator in between the operands (as in "1 + 1"; aka infix notation), you write it after the operands (as in "1 1 +"). RPN has the benefit of not requiring brackets since the operator precedence is simply based on where in the expression the operators are, instead of some arbitrarily decided hierarchy people came up with centuries ago.

dither_lut16("x 100 +") increases the luma of every pixel by 100, dither_lut16("x 100 -") decreases the luma likewise, and dither_lut16("x 2 *") doubles the luma of every pixel.

Keep in mind that with 16-bit video the range of valid luma values is from 4096 to 60160 for TV range and 0 to 65535 for full range; small changes like Ī1 don't have any visible effect unlike with 8-bit video.

If you really don't want to learn RPN, you can still use infix notation and the mt_polish helper function to convert from infix to RPN, like dither_lut16(mt_polish("((x/65535)^2)*65535")).
colours is offline   Reply With Quote
Old 28th June 2014, 08:00   #3  |  Link
raffriff42
Retried Guesser
 
raffriff42's Avatar
 
Join Date: Jun 2012
Posts: 1,377
SmoothAdjust plugin: SmoothLevels16
http://forum.doom9.org/showthread.php?t=154971

Your 0-255 range is now 0-65535, otherwise it's (closely) compatible with Levels:
Code:
  - SmoothLevels16( input_low, gamma, input_high, output_low, output_high, chroma, limiter, TVrange, preset,
                  Lmode, darkSTR, brightSTR, Ecurve, Ecenter, protect,
                  smooth, dither, useMT, useOPT, show, screenW, screenH, scale )
raffriff42 is offline   Reply With Quote
Old 28th June 2014, 16:19   #4  |  Link
bxyhxyh
Registered User
 
Join Date: Dec 2011
Posts: 347
Levels(coring=false) is
Code:
dither_lut16("x input_low - input_high input_low - / 1 gamma / ^ output_high output_low - * output_low +")
I still couldn't get Levels(coring=true)'s formula.

Also
16 (8bit) and 4096 (16bit) is not equal in avisynth!
255 (8bit) white is equal to 65535 (16bit) white.

Hence 16bit_value = 8bit_value * 257

Therefore 16 (8bit) is equal to 4112 (16bit).

Last edited by bxyhxyh; 28th June 2014 at 16:26.
bxyhxyh is offline   Reply With Quote
Old 28th June 2014, 16:38   #5  |  Link
Bloax
The speed of stupid
 
Bloax's Avatar
 
Join Date: Sep 2011
Posts: 319
It's 8bit_value * 256, because 255 and 65535 being the max values is simply an artifact of the values being 0 to (2^bits)-1, instead of 1 to 2^bits.

The 256x multiplier is explained by 2^16 being 2^(16-8) times bigger than 2^8. (And 2^8 just happens to equal 256)
Bloax is offline   Reply With Quote
Old 28th June 2014, 16:48   #6  |  Link
bxyhxyh
Registered User
 
Join Date: Dec 2011
Posts: 347
Quote:
Originally Posted by Bloax View Post
It's 8bit_value * 256, because 255 and 65535 being the max values is simply an artifact of the values being 0 to (2^bits)-1, instead of 1 to 2^bits.
Yes, you're right.
In math
0 = 0
1 = 256
.
.
.
255 = 65280
256 = 65536
This means 65535 (16bit) > 255 (8bit)

But for avisynth, 255 (8bit) is pure white and 65535 (16bit) is pure white. Therefore in avisynth, 255 (8bit) = 65535 (16bit).
So 16bit_value = 8bit_value * 257.

Last edited by bxyhxyh; 28th June 2014 at 17:06.
bxyhxyh is offline   Reply With Quote
Old 28th June 2014, 18:15   #7  |  Link
cretindesalpes
͡҉҉ ̵̡̢̛̗̘̙̜̝̞̟̠͇̊̋̌̍̎̏̿̿
 
cretindesalpes's Avatar
 
Join Date: Feb 2009
Location: No support in PM
Posts: 610
If youíre using TV-range, multiply the values by 256, so black and white are represented by 16<<16 and 235<<16 . With full range, multiply them by 257 so 0 and 255 are mapped to 0 and 65535.
__________________
dither 1.27.2 for AviSynth | avstp 1.0.3 for AviSynth development | fmtconv r19 for Vapoursynth | trimx264opt segmented encoding
cretindesalpes is offline   Reply With Quote
Old 28th June 2014, 18:36   #8  |  Link
StainlessS
HeartlessS Usurer
 
StainlessS's Avatar
 
Join Date: Dec 2009
Location: Over the rainbow
Posts: 5,653
Quote:
Originally Posted by cretindesalpes View Post
represented by 16<<16 and 235<<16 .
Perhaps 16<<8 and 235<<8.
__________________
I sometimes post sober.
StainlessS@MediaFire ::: AND/OR ::: StainlessS@SendSpace

"Some infinities are bigger than other infinities", but how many of them are infinitely bigger ???
StainlessS is offline   Reply With Quote
Old 28th June 2014, 18:57   #9  |  Link
cretindesalpes
͡҉҉ ̵̡̢̛̗̘̙̜̝̞̟̠͇̊̋̌̍̎̏̿̿
 
cretindesalpes's Avatar
 
Join Date: Feb 2009
Location: No support in PM
Posts: 610
Oh yes youíre right.
__________________
dither 1.27.2 for AviSynth | avstp 1.0.3 for AviSynth development | fmtconv r19 for Vapoursynth | trimx264opt segmented encoding
cretindesalpes is offline   Reply With Quote
Old 29th June 2014, 01:12   #10  |  Link
j7n
Registered User
 
j7n's Avatar
 
Join Date: Apr 2006
Posts: 80
This makes sense now. Thank you for the pointers. I've used another scripting language where the operators were separated (Cakewalk), and I can understand it now.

My installation of AviSynth appears to have a problem or a conflict, which prevented me from figuring out the syntax through trial and error. If I use dither_lut* with any "expr", luma always becomes black and chroma remains untouched.

Problem also occurs in a simple script of three lines. AVISource("124.avi").dither_lut8().ditherPost()

I have updated Dither to v1.24 (1.26 didn't work on XP), with no change. Resize, dither and gradfun work fine. What could be the reason?

If I can't solve this, I'll try SmoothAdjust.
j7n is offline   Reply With Quote
Old 29th June 2014, 03:04   #11  |  Link
cretindesalpes
͡҉҉ ̵̡̢̛̗̘̙̜̝̞̟̠͇̊̋̌̍̎̏̿̿
 
cretindesalpes's Avatar
 
Join Date: Feb 2009
Location: No support in PM
Posts: 610
Quote:
Originally Posted by j7n View Post
If I use dither_lut* with any "expr", luma always becomes black and chroma remains untouched.

Problem also occurs in a simple script of three lines. AVISource("124.avi").dither_lut8().ditherPost()
With dither_lut8, "x" on input is scaled to 8 bits (0Ė255, 128 for neutral chroma), but must be scaled to 16 bits on output (0Ė65535, 32768). Therefore without argument, dither_lut8 will keep the 8-bit values, reducing the contrast by 256.

About the chroma, the dither_lut* functions work like their Masktools equivalent. If you donít specify anything for u and v, the planes will not be processed and will contain random data, depending how the frame buffers are internally recycled by Avisynth. It could be something like the input frame content, but it could be anything else. To process the chroma, set u=3, v=3.

Quote:
Originally Posted by j7n View Post
I have updated Dither to v1.24 (1.26 didn't work on XP)
I didnít know that, and after a quick search it seems it is related to the switch to VS 2012. I changed the compilation target to XP for the 32-bit versions, so the next build should be compatible with XP again (same with all other projects Iím working on).
__________________
dither 1.27.2 for AviSynth | avstp 1.0.3 for AviSynth development | fmtconv r19 for Vapoursynth | trimx264opt segmented encoding
cretindesalpes is offline   Reply With Quote
Old 30th June 2014, 11:30   #12  |  Link
j7n
Registered User
 
j7n's Avatar
 
Join Date: Apr 2006
Posts: 80
The problem of the function not working was caused by a loaded build 36 of mt_masktools, which I had installed as a dependency for another plugin. Replacing that with build a48, as required in the documentation, made dither_lut16 work correctly. I stand corrected about what dither_lut8 does. I incorrectly assumed it was just a shorthand for convert_8_to_16 and lut16.

I have a working Levels16 based on bxyhxyh's formula.

SmoothAdjust appears to work with Dither's stacked clip format. But it currently doesn't load on the older of my two PCs, which is inconvenient. A good choice otherwise, since it's just a single DLL.
j7n is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +1. The time now is 07:20.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2018, vBulletin Solutions Inc.