SOME (NOT SO) SHORT THOUGHTS ON COLOR (LUMA) PROBLEMS WHEN EXPORTING TO QUICKTIME

    The cold, snowy December days give me lots of time to think about editing and the problems I've had with color mapping; and, proper luma ranges when exporting video from Media Composer to Quicktime Movie and Quicktime Reference. I have a theory why there is apparently so much misunderstanding about exporting to Quicktime formats, so, I thought I'd write it down.

First, to understand my theory, one needs to understand that conventional 8-bit imaging color mapping falls into two categories. The original color mapping was done for silver halide and film production. In this case, 8-bit colors are divided into 256 steps for each primary color of red, green and blue, defined by black at a value of 0, 0, 0 RGB; and, white is defined as a value of 254, 254, 254 RGB. All colors fall in between these two values, for example, pure red is an RGB value of 254, 0, 0, and pure blue is 0, 0, 254, and so on.

The second category of color mapping was developed for broadcast television, in which the original color mapping was changed to a smaller range of 16, 16, 16 RGB to 235, 235, 235 RGB. Without an explanation of why this was done, it is a smaller range within the original film range. Media Composer works, by default, with this broadcast television range of values, also known as Rec 601/709.

OK so far? Now, we have the introduction of the world wide web, in which video color mapping was defined by the old film standards of RGB 0, 0, 0 to 254, 254, 254. With the introduction of video imaging for the web, some playback applications were designed to work within this full range of 0 to 254, and some applications were designed to only work within the broadcast video range of 16-235. For example, Windows Media Video works with the web range, and Quicktime works with the web range. SDV  and HDV work in the broadcast color range of 16-235. JPEG images are full RGB, like QT.

So, what does this mean? It means the editor has to start thinking about his delivery media, and what color mapping is appropriate for the delivery format….film, broadcast, or web. As a further complication, the computer monitor used by the editor is displaying images in web colors, not necessarily broadcast or film colors. Media Composer functions, by default, in the broadcast range of color mapping on the timeline, however, the editor is given several options for importing, exporting, and displaying in the source/record windows. When the editor chooses to export to Quicktime, for example, whether he/she recognizes it or not, they have chosen the web range of color mapping, since this is how Quicktime is designed to work. This means that anytime the editor imports or exports into or from the Quicktime wrapper, the application is expecting to get or generate video color mapping values of RGB 0 to RGB 254.

All editors accustomed to delivery for broadcast TV, will color correct their video stream to fall within the color mapping range of 16-235. Even Media Composer shows color values outside of 16-235 as "white" instead of green on the MC Color Correction waveform monitor. Then a color correction filter is applied by the editor to remap everything to within the range of 16-235. This is fine for broadcast delivery, but, what about web delivery. And considering that Quicktime is designed for web delivery, the codec application within the Quicktime wrapper is expecting to get color values in the range of 0-254. Now, if the editor has applied a color correction to limit the video on the timeline to 16-235, what will happen is that the encoded quicktime video will wrap the 16-235 video within the 0-255 native color range. All values below RGB16 will appear as RGB 0, and all values above RGB235 will appear as RGB 255.

Now, this broadcast color video within the web quicktime wrapper is imported to another application like After Effects. If the defailt values of AE are used, it will expect to see quicktime imports as having a color range of 0-254. After Effects is a good program, and will assume the editor is wanting to work to broadcast standards of 16-235. All AE will know is that the editor is importing a quicktime video, so, being the good program that it is, it will remap all the color values of quicktime to color values of broadcast.

BUT, the video within the quicktime wrapper is already limited to broadcast standards by the color correction filter applied in Avid. So, AE has remapped the video color range of the quicktime to 32-215, resulting in a very washed out and low contrast image stream. The image looks even worse when being displayed by a computer monitor designed for RGB 0-254.

So, Quicktime really doesn't have a color mapping bug, as some people have suggested. It's working exactly as designed, and wrapping whatever it gets in the expected color range wrapper of 0-254 to the values of 16-235. The correct workflow, back in Avid, would be to export a color range in the timeline of 0-254 and use full RGB when exporting to a web based delivery format like Quicktime. And, as a side observation, exporting from Media Composer as 601/709 or full RGB will make NO DIFFERENCE if you're exporting to Quicktime and you've already limited the color values on the timeline to 16-235.

I hope this rather wordy explanation makes sense to anyone who has read this far. If something I've theorized seems wrong, please don't hesitate to say so. I woul hate to be delusional in my thinking…or cause anyone else to have a delusion about why this happens.

xw8200 SCSI channel sharing

I am considering adding a SATA card and my only slot options are slots 6 or 7, which share the same bus as the SCSI controller.  Does anyone think that doing this will adversly effect my SCSI drive performance?  I currently have only two ultra 320 73gigs, one on each channel.  The reason i am adding the satas is because they are left over from a nas.

My specs:

xw8200

MC 2.8

Two internal sata ports are in use by system drive and 2nd sata drive.

Thanks,

Brian LeCrone (BigB)

Correcting White Balance
In this Final Cut tutorial, Richard Harrington discusses what to do to correct your film when you shoot footage with the wrong white balance setting. This is a common problem if you step outside after shooting inside and you forget to rewhite balance. Richard uses the three way color corrector to do