تصحيح الألوان correct colors with levels filters

This tutorial will help you to know more about video levels and the "Levels" filter in Sony
Vegas® software. Understanding how to adjust and manipulate video levels will help put you in control of what the audience sees. By understanding levels, you will be able to avoid undesirable or unintentional clipping in the image. It will also assist you in improving your footage.
To achieve good video levels with the Levels filter, you will first need to know what those levels should be.

What Video Levels DV Cameras Record At

DV cameras typically record "superwhites"- values above digital white level. These are "illegal" values which may not be displayed correctly when broadcast or played on a DVD player. Broadcasters may reject your master if it has too many superwhites (this may depend on the broadcaster). If your target delivery format is DVD, some (but not all) DVD players will clip superwhites. Clipped white values will lack detail and may look ugly, being washed out or even appear to vibrate.

Some DV cameras such as the PD150, DSR250, and DVX100 have menu settings named something similar to "7.5% setup". What this setting actually does is to raise the digital black level recorded to a non-standard digital black level (see Adam Wilt's DV FAQ for more detail). This 'fake setup' could be problematic. The Levels filter may be employed to repair any difficulty caused by the non-standard levels.

DV cameras will also record values slightly under digital black level due to digital compression. You should let those values fall under digital black level.

Proper Video Levels

The following paragraphs will describe what video levels should be for the analog and digital domains.

Proper Levels for Computer Formats (i.e. web streaming)

Computer white level should be at 255 255 255 RGB. Black level should be at 0 0 0 RGB. Sony Vegas calls this "computer RGB".
If you are creating video exlusively for computer formats, use the following settings when you follow this tutorial. In the Video Scopes settings (described below), uncheck the "Studio RGB 16 to 235" and "7.5 IRE Setup" settings.
If you are targeting video distribution primarily, but need to make a web version of your footage then use an additional Levels filter in the Video Output FX chain. Use the "Studio RGB to Computer RGB" preset.

Proper Digital White and Black Level

In Sony Vegas, proper digital levels depends on the DV codec being used.

Sony, Canopus DV codecs: Black level should be at 16 16 16 RGB. White level should be at 235 235 235 RGB. Vegas calls this "Studio RGB (16 to 235)".

Microsoft, Matrox, MainConcept, Apple Quicktime DV codecs: Blacks level should be at 0 0 0 RGB. White level should be at 255 255 255 RGB.

This tutorial assumes you are using the Sony DV codec used by Sony Vegas, which is the codec you should use (at least for this tutorial). To ensure that you are using the Sony DV codec, go to Options --> Preferences. Under the General tab, check "Ignore third party DV codecs", uncheck "Use Microsoft DV codec".



Also check the settings for Vegas' Video Scopes. These settings affect how digital black levels are represented on the Waveform display in the Video Scopes.



To bring up the Video Scopes window, go to View --> Video Scopes. Or use the shortcut: Crtl Alt 2.
A: Click this button to bring up the Video Scopes Settings window.
B: The "Studio RGB (16 to 235)" setting should be set depending on which DV codec you are using. For the Sony DV codec, check this box.
C: The "7.5 IRE Setup" setting controls where digital black level (16 16 16 RGB in this case) is represented on the Waveform display. If this setting is unchecked, digital black level will be displayed at 0 on the waveform display. If this setting is checked, digital black level will be displayed at 7.5. You should know if this setting is on.
Please note: This setting does not affect your video levels.
D: This button toggles the "Update Scopes while Playing" setting. I suggest turning this setting on. You can adjust Levels on a clip as it is looping (double click on the center of a clip to set the loop region to the clip; hit "q" to toggle Loop Playback).

Digital white level corresponds to 100 on the Waveform display (of the Video Scopes) as long as the "Studio RGB (16 to 235)" setting is correctly checked/unchecked.

In the Video Preview window in Vegas, digital white level will appear a 235 235 235 RGB. This will be problematic for monitoring on a computer display, as whites may look a little grey-ish. The same applies for black. Digital black level will appear as 16 16 16 RGB on your computer monitor (where 0 0 0 RGB is the lowest your computer monitor can go). What this means is that you should view your image on an external monitor (scroll down for HDV information). The most common external monitor to use is a consumer television hooked up to your DV camera (which can act as a digital-analog converter; most can do this). To do this:

Click on the "TV" icon in the Video Preview window.

 

 

Turn on your DV device, and put it into VTR or VCR mode.
On your DV device (i.e. camera, deck, etc.) make sure that it is converting video in the right direction (many devices can convert analog to digital). On many DV cameras, this setting is called "DV --> A/V OUT". Make sure it is set to on.
On your TV (or better yet, broadcast monitor) check that it is set to the right input.
If you don't see anything, try power cycling your DV device.
If you still don't see anything, go to Options --> Preferences --> Preview Device. Check that the Device is "OHCI Compliant IEEE 1394/DV".
There is a tutorial on connecting an external monitor to your camcorder or other Firewire converting device here.

For HDV editing, you may want to a secondary Windows display instead. In this case, enable the color management settings so that video is displayed correctly. In the Preview Device settings (Options --> Preferences --> Preview Device):

Check "Use color management".
Check "Use Studio RGB (16 to 235)".
Analog Levels

For NTSC, analog white level should be at 100 IRE.

For NTSC (other than Japan), analog black level should be at 7.5 IRE. This is also referred to as (7.5 IRE) "setup" and (7.5 IRE) "pedestal".
Japan's version of NTSC (NTSC-J) has analog black level at 0IRE.

PAL has analog white level at 100 IRE, and analog black level at 0 IRE.

Digital-analog conversions

Most consumer and "prosumer" video equipment for the North American market will translate proper digital black level to 0 IRE (instead of 7.5 IRE). This will result in crushed/clipped shadow detail and an image that is slightly too dark.

DVD players will translate proper digital black level to 7.5 IRE.

This issue is important because it can affect how your footage appears. If your digital-analog converter does not add 7.5 IRE setup, you will be monitoring with an image that is too dark and has clipped shadow detail.

If you are monitoring via a consumer DV camera (that converts digital black level to 0 IRE instead of 7.5 IRE) and your target format is DVD:

Calibrate your monitor so that it recognizes black level at 0IRE. To do this:
Create a new project in Sony Vegas. A new project ensures that there are no Track level or Video Preview FX that may affect video output.
Drop the "SMPTE Bars" test pattern from "Media Generators" -> "Test Pattern" into the timeline. Hold shift as you drop the media to prevent the Video Event FX dialog from popping up.
Your external monitor should have a "brightness" control and a "picture"/"contrast" control. Brightness controls black level while picture/contrast controls white level. You will be adjusting the brightness control.
In the SMPTE Bars test pattern, you should see the three PLUGE (Picture Lineup Generating Equipment) bars. If not, increase the brightness control until you do. The three yellow arrows below point to the PLUGE bars.

 

In the analog domain, these bars are supposed to be 3.5IRE, 7.5IRE, and 11.5IRE. The leftmost 3.5 IRE bar should be below analog black level. Hence, you should not be able to tell it apart from the middle bar (which represents black level). Adjust the brightness control just until the middle bar is indistinguishable from the leftmost bar. The rightmost bar should still be visible. If not, turn up brightness until you see a dividing line between the right and middle bar. You should not see a dividing line between the left and middle bars. With PLUGE set correctly, you should see something like the following:

 

Your monitor will now display white and black levels from Vegas correctly. While color correcting in Vegas, keep proper digital levels. When you burn your DVD(s), your levels will be correct since DVD players will convert digital black level to analog black level correctly.
Be aware that other sources feeding into your monitor may be displayed incorrectly, depending on whether or not the source device translates digital black level incorrectly.
If you are targeting an analog format and your digital-analog converter converts digital black level to 0IRE, then things get tricky. You have a few options:

A- If it is an analog dub (i.e. a VHS for client proofing), then it may be OK to let the incorrect conversion occur.
B- If it is an analog dub, you can first burn a DVD and then make the dub off the DVD player. DVD players will convert video levels correctly.
C- Use a proc amp to add setup.
D- Buy a digital-analog converter that converts video levels correctly. This is probably the best solution.
E- Add 'fake' setup. In Vegas, one method of doing this is to raise black level via the Color Corrector filter (gain = 0.927, offset = 17.2).**

تابعو الجزء الثاني