Histogram Explained

[Chris Young]

Brad ~

Super fine ‘Grading’.

Just a little exercise might make it clearer. Create a new instance of Vegas. Have your Vector/Waveform/Histogram up. Select a bright sunny outdoor clip to make it easy. Look at the waveform monitor and most likely the peak video levels are around 110 on the scale. On the histogram these levels might be around the 255 level. Now install the Sony Color Corrector plugin on this clip. Next slide your cursor back and forth in the histogram window until you have the highest peak of the histogram under it. Up in the top right corner of the histogram is a figure that will change when you move the cursor. For this example lets say it says 53 at the highest point of the histogram.

Now use the ‘Gain’ slider in the color corrector and adjust the peak video level down to 100 on the waveform, 1 volt peak in broadcast video terms. You will notice that the picture gets a little darker overall due to the reduced range. Now look for the histogram peak level and it may be down to something like 46 at the highest point. Now adjust the ‘Gamma’ slider in the CC until the histogram peak point comes back up to 53 or thereabouts.

The result is a picture with the correct peak levels but that didn’t darken up too much when the peaks were reduced because you adjusted the gamma peak back to what the histogram originally displayed, 53. This adjustment will also lift the black threshold slightly usually giving you more details in the dark areas of the picture. If you want to keep these areas dark the careful adjustment of the ‘Offset’ slider in conjunction with the ‘Gain’ and ‘Gamma’ sliders will enable you to fine tune a picture that looks good but meets all broadcast specs re levels.

Chris Young
CYV Productions
Sydney

[Theo Van laar]

The histogram is also very usefull when you apply the effects LEVELS or COLOR CURVES to adjust brightness and contrast of your events.

Theo