From BlenderWiki
In addition to being a work area for arranging video strips, the VSE workspace can show you different aspects of the composite result, for the current frame:
- Chroma: Color hue and saturation
- Luma: Brightness/contrast
- Image: Colors (what you see)
- Sequence: Video strips
In the Chroma, Luma, and Image modes, a channel selector appears; channel 0 is the result of compositing the strips with their special effects strips. Channel 1 is what the current frame's image from the strip in channel 1 looks like (channel 1 is at the bottom of the heap). The display of these modes is either the composite (channel 0) or the frame from the strip (channels 1 through n).
Zoom the view of any of these workspaces by scrolling your middle mouse wheel.
Chroma Vectorscope
For the selected channel, this display shows the colorspace of the image inside a hexagon. Each point of the hexagon is a primary color: red, magenta, blue, cyan, green, and yellow. Black is at the center, and overall saturation is scaled as dots closer to the outside. The example to the right shows that the image has a lot of red (50% saturation) and small amount of blue, with no green.
Use this display to check for too much color saturation. While over-saturated images look great for op-art and computer displays, they stink when shown on the big screen TV. Use the Alt-Animation key to scrub the video; this display will update with a new/revised map for each frame. Just like watching the Image preview to see what it looks like, watch the Chroma Vectorscope to watch for color use.
Luma Waveform
For the selected channel, brightness, or luminosity, is mapped with this display.
Note:
The original explanation seems – to me – quite confused, so I proposes here my own interpretation of this mode (deduced from my experiments)… If someone knows more about it, please correct it!
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In this mode, the vertical axis represents the luminosity: null (full black) at the bottom, full (full white) at the top; the horizontal axis is a mapping from the horizontal axis of the frame. There are as much curves as lines in the frame: each one of this curves represents the luminosity of the pixels of one line. Moreover, the color of a pixel in this mode represents the number of pixels from the matching column of the frame sharing the same luminosity – i.e. the number of curves that cross at this point (black/transparent, for no pixel, white/opaque for at least 3 (?) pixels).
It's not easy to explain, try it with various pictures (rather with natural pictures, the curves are more easy to see) and you might understand better. Look at the two examples below, too.
 'Simple' picture. The various horizontal lines in the Luma waveform match the uniform-color lines of the picture. Note that the 'grey 20%' one-pixel width line (inside the yellow strip) is represented in the Luma waveform by a grey line. The two lines drawing an 'X' are from the two linear tone shades (white→black and black→white). Finally, the broken line matches the complex tone shade at the bottom of the picture. |  A 'real' picture. The curves are quite visible. We found a luma of 80-100% for the sky, a luma around 40% for the sea, and a luma of 10-20% for the mountains, growing around 40% for the sunny part. |
| Examples of VSE Luma Previews. Note that the pictures (first green frame, at the top) are only 50px high, to limit the number of curves displayed in the Luma waveform! | |
Use this display to check for appropriate contrast and luminosity across all frames in the channel. When spots in the film that should have even illumination don't, it looks like a flashbulb went off or an extra light was suddently turned on. This can happen if two strips were rendered or shot under different lighting conditions but are supposed to be contiguous.
Image Preview
In the upper right window pane of the Sequence screen layout is another VSE window, this one set to Image Preview mode. It shows you what the resulting video will look like when saved.
Sequence Mode
The main working mode for adding strips and moving them around, cutting, grouping (making meta) and splicing them through special effects.
