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Mac AVCHD gamma issues - the fix


Andrew Reid

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[img]http://www.eoshd.com/wp-content/uploads/2012/07/fs100-slrmagic-hyperprime.jpg[/img] As I recently discovered Macs really seem to hurt your AVCHD footage from the FS100, GH2 and NEX cameras. Es

These are not exactly new "problems". Stu Maschwitz describes the limiting of values (that is cutting off blacks and whites) in his [i]DV Rebel[/i], and for DV, hence the name. I didn't understand why

O dont have FCP x only PPro so Fix is for P Pro cs5.5 cs6

[quote name='rjett' timestamp='1343420566' post='14649']
I too would like a translation of "the fix" for FCP X. We would be very grateful.
Thanks, Richard Jett
[/quote]

Apparently there is a misinterpretation for the Sony NEX cameras, no problem for EOS or GH2, neither in Premiere nor old or new FC. yellow said it in the first 5D2RGB- Thread, and I think it is true for NEX also:

[color=#222222][font='Helvetica Neue', Arial, Verdana, sans-serif][size=4][background=rgb(255, 255, 255)]

[quote name='yellow' timestamp='1341272770' post='13363']But as mentioned previously if using a 32bit float NLE then there's really no need to transcode and squeeze levels, just grade in the NLE or a levels mapping, all the data will be there outside of the 16 - 235 range just the preview will appear crushed and clipped as the 'proper' range for 8bit playback is 16 - 235 ...
[/quote][/background][/size][/font][/color]
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[b] [url="http://www.eoshd.com/comments/user/13863-hmcindie/"]hmcindie[/url] [/b]

[b] [/b]


U r not getting this are u ... Mac and Windows have same issues with sonys avchd output files. This beacause the files are 16-255. so u get unnatural roll off in highlights and less dynamic range due to clipping them. U have to bring them back with the fast colour corrector!
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[quote name='EOSHD' timestamp='1343651529' post='14721']
Not the individual MTS, you have to have the whole folder structure intact and open that in Quicktime with a double click.
[/quote]

With the "[url="https://eww.pass.panasonic.co.jp/pro-av/support/desk/e/download.htm#avccamip"]Panasonic AVCCAM importer plugin[/url]" (a plugin for Quicktime), QT plays back AVCHD from Panasonic cameras (like GH2) and (as QT7 Pro) exports conversions. Mpeg Streamclip then also does this, useful for batch-conversions.

Also, if you open a folder full of mts-files, after a few moments thumbnails of the clips are created, they can be browsed with coverflow asf.

This is particularly handy for comparing originals to ProRes-converted copies, because with QT-player you can have them run side by side.
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I just checked some GH1 footage with blown highlights due to a strong spotlight moved across a stage.
(Camera was covering an event unattended with auto-exposure on matrix mode while I was busy shooting a more important event.)
The footage was imported directly from the SD card into FCPX. From what I see in the video scopes the blacks do start at 0 but the blown highlights peak at 100% but do roll off a bit behind that point.
Reducing the highlights by the -8% calculated above seems to match up with the very end of that rolloff.
Comparing at 200% it looks like I get at least a tiny bit of detail back at the edges of some of the blown out areas. I may however be mistaken as the change of brightness may trick my eye.

Can someone confirm this on GH1 and GH2? Possibly with a shot of a grey gradient or something.
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[b] [url="http://www.eoshd.com/comments/user/18253-marcuswolschon/"]marcuswolschon[/url][/b]

Dont have a GH2 here but because the GH 2 is 16-235 this isnt much of a problem with blown highlights. On a Sony using this fix u get much more highlight detail... and overall dynamic range (about 3-4 stops) because of 16-255.
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So for those with FCPX like myself, How can one recover the grey in between white and black for the DR, when Quicktime screw our GH2 footage.. I like the Input and Output tool wit the range, reminds me of editing photos with Aperature or iPhoto.. But FCPX doesn't have this kind of editing of exposure or I haven't found it yet..
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⌘7 opens the videoscopes window. In the dropdown menu choose the >Waveform >Luma (this could be your standard videoscope, FCP always displays your latest choice on next start). This shows you a "scientific" representation of what's there. The legal parts live between 0 and 100, what is called broadcast range. Being the uppity DSLR freshmen we are, we dismiss this shit, and "bring the values into the range". You should not believe in any 8% rule, this is just changing one ancestral wisdom for the next. You should color correct using the exposure window and the balls for highlights and shadows whilst watching the lines in the waveforms.

What I guess from the questions about any ominous workflow, there seems to be some insecurity of what acutally should be done.

Don't be too scientific. You do this for a better looking image, so please trust your eyes!

What is suspected by the lovers of 5D2RGB is that Quicktime cuts of values because it misinterprets the ranges. With 5D2RGB you can manually override the broadcast flags and choose full range for any footage.

FCP X can edit all your footage natively. Of course, you really should have Lion (wait a few weeks before upgrading to 10.8, Mountain Lion, there seem to be sum bugs still) to complete the AV-Foundation framework. There you can easily judge for yourself, if a file from your own camera is treated better with 5D2RGB (download the lite-version, it's free) than as original or transcoded by FCP X to optimized media (ProRes as well). With material from 7D and GH2 I found there was nothing lost (judged by the waveform) with any of the methods.

If you feel better then, buy the batch-ability of 5D2RGB and check [i]full range[/i] before you hit [i]convert. [/i]Note, that the values now do not fit into 0-100 in the other direction: The lowest values don't touch zero, the highest (even if clearly flatline-clipped) don't touch one hundred. Left to my own devices, I would interpret this as an actually [i]narrowed[/i] range, as baked-in false values.
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[quote name='AdR' timestamp='1343782074' post='14766']
@alexander, how did you measure GH2 footage and get 16-235? When I check it, I see 16-255, which gives it the same problems as the Sony.
[/quote]

AdR & alexander, how do you measure GH2 (or any) footage and get to ("when I check it") the values you found?
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[quote name='Axel' timestamp='1343809697' post='14774']
AdR & alexander, how do you measure GH2 (or any) footage and get to ("when I check it") the values you found?
[/quote]

That's part of the problem, especially with h.264 footage, because many apps scale the luma when they see the h.264 flag in the meta data.

The two methods I've used are:

(1) Open the files in QT7 (which I have heard ignores scaling flags), then take a screengrab and open in photoshop. Use Info Window and Levels histogram to determine luma scale.

(2) Set up AE CS6 with color space of Adobe RGB(1998), and import .mts file, then use Synthetic Aperture for scopes and histograms. (I believe using Adobe RGB (1998) causes AE to import the .mts file without any luma scaling.)

If anyone has better methods, please post them.
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