Home » Blogs » Granjow's blog Kdenlive Free and open source video editor for GNU/Linux, Mac OS X and FreeBSD Introducing Color Scopes: The Vectorscope Submitted by Granjow on Sun, 10/10/2010 - 18:30 The last scope (after the Histogram and the Waveform and RGB Parade) that is new to kdenlive 0.7.8 is the Vectorscope. This is actually the most interesting scope because it is quite different from the other ones and, secondly, is really useful for Color Grading. More in the full article » How the Vectorscope works There is one simple thing that makes the Vectorscope so special: It uses a color space different than RGB. That sounds unspectacular, but it is not. The previous scopes allow you to determine which brightness values exist in your image, the Vectorscope shows which colors there are. The Vectorscope supports two different color spaces: YUV and YPbPr. Both of them have the Y in common, something you know from before: It is the Luma component. (Rec.601 in both cases.) This, amongst others, comes from black/white TV. When Color TV was introduced, some people actually recognized that not everybody would immediately trash his old b/w TV and buy a new one, so they still sent the b/w signal, but with two additional channels: The blue difference and the red difference (to Luma), called U and V. So that is how YUV works (please take a look at the image in its YUV components on the linked Wikipedia page). The other color space, Y PbPr or its digital counterpart YCbCr respectively, are similar. If you switch between the two color models in the Vectorscope (via the context menu) you will notice that the colors are slightly shifted. Y CbCr is used basically everywhere in digital video. So, what the Vectorscope does: It calculates the Luma value of a pixel, then calculates the blue difference/red difference values. Then it throws the Luma value away. Why that? It is because the Vectorscope is 2-dimensional. The blue difference is on the horizontal axis, the red difference is on the vertical axis. (There actually are three-dimensional vectorscopes which put the Luma component on the third axis!) Vectorscope example: Grayscale video Now let’s take a look at how this actually looks like in a video.
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Home » Blogs » Granjow's blog
KdenliveFree and open source video editor for GNU/Linux, Mac OS X and FreeBSD
Introducing Color Scopes: The VectorscopeSubmitted by Granjow on Sun, 10/10/2010 - 18:30
The last scope (after the Histogram and the Waveform and RGB Parade) that is new to kdenlive 0.7.8 is the Vectorscope. This is actually
the most interesting scope because it is quite different from the other ones and, secondly, is really useful for Color Grading.
More in the full article »
How the Vectorscope worksThere is one simple thing that makes the Vectorscope so special: It uses a color space different than RGB. That sounds unspectacular, but it
is not. The previous scopes allow you to determine which brightness values exist in your image, the Vectorscope shows which colors there
are.
The Vectorscope supports two different color spaces: YUV and YPbPr. Both of them have the Y in common, something you know from
before: It is the Luma component. (Rec.601 in both cases.) This, amongst others, comes from black/white TV. When Color TV was
introduced, some people actually recognized that not everybody would immediately trash his old b/w TV and buy a new one, so they still
sent the b/w signal, but with two additional channels: The blue difference and the red difference (to Luma), called U and V. So that is how
YUV works (please take a look at the image in its YUV components on the linked Wikipedia page).
The other color space, YPbPr or its digital counterpart YCbCr respectively, are similar. If you switch between the two color models in the
Vectorscope (via the context menu) you will notice that the colors are slightly shifted. YCbCr is used basically everywhere in digital video.
So, what the Vectorscope does: It calculates the Luma value of a pixel, then calculates the blue difference/red difference values. Then it
throws the Luma value away. Why that? It is because the Vectorscope is 2-dimensional. The blue difference is on the horizontal axis, the red
difference is on the vertical axis. (There actually are three-dimensional vectorscopes which put the Luma component on the third axis!)
Vectorscope example: Grayscale video
Now let’s take a look at how this actually looks like in a video.
accurate article about chromatic aberration) in lenses, artifacts in the recorded video file. So usually neutral areas will not share one single
pixel in the vectorscope but have a certain diameter. Therefore the padding.
Because this is a suitable clip for hue:
Now what happened here? The hue has changed, and the points on the scope look like rotated by 30 degrees. And indeed they did rotate. The
Hueshift effect changes the hue of all colors by a certain (configurable ;)) amount. In the Vectorscope this becomes visible as a rotation
around the center of the scope.
Similarly, when changing the saturation/chroma, the dots on the vectorscope will move closer to the center or further away from it.
Creating a look for your videoIn the Histogram article’s introduction I mentioned creating looks with color correction. This example covers part of the tip of the iceberg of
this topic. (The tip is the most important part of an iceberg because it tells you where you can drive safely ;))
What is special about creating a look for a video? Let’s take a look at some random clips:
Mostly different content and therefore different colors – as said: random. One point of Color Grading is to give single clips a connection.
This is not limited to white balance only. White balancing a clip is about removing color casts (which is a good thing because it gives you a
neutral starting point). But we can also add new colors.