Thanks. That was an interesting discussion. The OP in that thread asked basically the same thing as I did. While the thread and the links in it contained a lot of good information, I don't think anyone directly answered the OP's (and my) original question regarding what is meant by "start" and "end". Start and end of what? Also "input" and "output" are not clear to me in the context of the levels setting.

Glenn Chan's tutorial is one of the best I know of. But without a working knowledge of levels in Photoshop (don't know how they're handled in PS Elements), it is going to be an uphill climb.

Levels in digital imaging fill a predefined range of 0-255. 0 is pure digital black, and 255 is pure digital white (for luminance), or the maximum color levels (chroma). In its most basic sense, luminance is the mean of the three chroma levels (this is not entirely accurate). 0-255 is a logarithmic scale, which creates a linear graded representation of the exponential curve of light levels. Any output below 0 or above 255 will crush or clip, respectively.

The input levels are the start/end points of your source media. Adjusting them will expand your linear range toward black or white, respectively. Usually there is no point in changing them, unless your video is extremely flat. Taking them outside of gamut will destroy shadow and highlight detail, which cannot be recovered in the rendered video. The output levels are the start/end points of the filter's output. Adjusting them will compress the levels toward the white or black end of the scale, respectively, effectively setting the min/max levels. This is useful for reducing the range to legal broadcast levels. To see the relationships, play with the controls and see what they do, which is a better learning method than reading a description. What you choose depends on whether you need to stretch or compress from either end of the scale.

Gamma shifts the midtone emphasis without affecting the output in/out points, with 1 being linear. This is a very difficult concept to understand, and can take years to master.

The levels control in Vegas is very similar to Photoshop, so playing with them in that environment will enhance the learning process as well.

Depending on your intended use, levels for video distribution will be kept within 0-255 (Computer RGB) or 16-235 (Studio RGB), but that is a separate discussion.

Here is a calibrated grayscale you can use to test the effects of input and output min/max points in your preview.

In making basic levels decisions in your workflow, you need to ask yourself four questions:

-- What is my baseline black level going to be?
-- What amount of shadow detail do I wish to preserve?
-- What is my maximum white level going to be?
-- How much highlight detail do I wish to preserve?

Understanding those four basic concepts, as well as understand that you can't put back what isn't there, the next step is practice, practice, practice.

musicvid,

thanks for that thorough explanation and the image you provided. I will use the image to experiment with the various settings to get a better feel for what they do.

In terms of using Photoshop (or PS Elements), have a look at Photoshop for Video by Richard Harrington. He discusses this in one of the first chapters.