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Mac AVCHD gamma issues - the fix

Andrew Reid

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As I recently discovered Macs really seem to hurt your AVCHD footage from the FS100, GH2 and NEX cameras. Especially the Sony FS100.

It is no wonder these cameras often get a bad reputation for limited dynamic range, crushed shadows and blown highlights - when you are only seeing the middle part of the full 8bit range of luma.

This Rec.709 portion of a 601 space (16-235 instead of the full 0-255 the FS100 shoots in) is incorrectly remapped to 0-255 by Quicktime. Therefore apps that use Quicktime at their core like Premiere, trip up. This makes a huge difference to the image. When fixed, you recover over 10% of your dynamic range, highlight and shadow detail, along with a much smoother roll off to whites and blacks.
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EOSHD Pro Color 5 for Sony cameras EOSHD Z LOG for Nikon CamerasEOSHD C-LOG and Film Profiles for All Canon DSLRs
So, what would be a good workflow?

I recently loaded a few .mts clips from my GH1 on a SCRATCH system running on Mac. SCRATCH has the option to recover the full color range of the clips. They also played smoothly... but didn't spend to much time on it.
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[quote name='gene_can_sing' timestamp='1343349741' post='14573']
Hey Andrew,

Does this fix make the AVC clip identical to what you would get out of 5DtoRGB in terms of how it displays on screen as well as dynamic range?

Thanks for the tip.


5DToRGB ProRes on the left, native (fixed) AVCHD on the right.

There is a very slight difference in saturation, nothing else.
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Have you two even read the blog?! :mellow:

Under the heading...

'The fix'

[color=#333333][font=Georgia, 'Times New Roman', 'Bitstream Charter', Times, serif][size=3]
(In Premiere Pro) The specific part of the Fast Color Corrector you need to apply the fix with is the Output Levels.[/size][/font][/color][color=#333333][font=Georgia, 'Times New Roman', 'Bitstream Charter', Times, serif][size=3]
Keep the Input Levels at 0-255 but change the [b]Output Levels to 15-235[/b].[/size][/font][/color]
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I think I figured it out in FCPX. I just used the built-in color corrector.

The exposure levels in FCPX aren't numbered 0-255, they're percentages (0-100).

So I figure bringing it up by 15/255 at the low end equates to 5.88%, so bring the blacks up by 6%.
The high end is to be lowered by 20/255, which equates to 7.84%, so bring the highlights down by 8%.

The resultant waveform looked similar to the waveform of the footage transcoded in 5DtoRGB. Not exact, but pretty much the same.

And a slight difference in saturation, like Andrew said earlier. The graded down footage it a bit more saturated.

[b]But someone please tell me if I'm wrong in my theory, like if the FCPX color corrector works in a different way or something. I'm not an expert. But the scopes seem to agree, for me at least.[/b]
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Don't you think it's still worth it to always get it through 5DtoRGB because of its compression artifacts removal capabilities?
Maybe it's not as noticeable on a high bitrate hacked GH2, but the results are quite good on Canon DSLRs.
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Thanks a lot!!!
[b] [url="http://www.eoshd.com/comments/user/13955-sfrancis928/"]sfrancis928[/url]:[/b]

[b] I'll try your settings on some footage and verify if they have any effect on bringing out more details in blacks and highlights.[/b]

(How to get rid of this bold text whe you copy someone's username?)
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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, it has to do with broadcast safety or what have you.The "fix" is quite simple: In your NLE (not limited to Premiere or FCP) open the luma waveform monitor. This should have a y-axis from 0 to 100. Lower the highlights until they all are crumbled under the "100"-line (some of them will go to 110 or so) and you'll get better defined whites, raise the shadows to "0", but not higher or you will get fog. Do all this with 32-bit floating point precision.
[color=#ff0000]Premiere[/color] shows you the quality of any filter as an icon right to the filter's name in the list, it is something like a folder with "32" in the middle. The [i]fast color corrector[/i] i.e. has it. Never use just one effect without the 32bit-icon!
[color=#ff0000]FCP7[/color] does [i]not[/i] show you if a filter uses 8-bit or 32-bit. There is this [url="http://documentation.apple.com/en/finalcutpro/usermanual/index.html#chapter=65%26section=2%26tasks=true"]list[/url], however, and there you see the little ¹ that indicates 32-bit-filters, the Color-Correctors are among them. As you can see, there are also many, many effects without 32-bit rendering. Don't use them. Let these things be done by Motion (where you change the bit depths in the projects properties, as in After Effects).
In [color=#ff0000]FCP X[/color] grading is not only completely done with highest precision, it is also no longer an effect, but just the always available [i]info[/i] of the clip - just never, never, never use the secret analyzing, auto-balancing and autocorrecting method FCP X offers you when you import media!

I tried the different settings of 5D2RGB, I tried ordinary Quicktime (did you know, that there is no gammashift in Quicktime anymore since Lion?), I tried .mov (7D) and .mts (GH2) as originals in Premiere, and I didn't find any permanent damage to the footage with any of the methods - as long as you do the contrast balancing described above manually and don't just hit [i]auto balance[/i].

5D2RGB is useful though for FCP X, because you may not have Cinema Tools, that allowed you to flag a clip with a different frame rate (within Premiere you right-click >[i]interpret footage[/i] and change the frame rate). During transcoding 5D2RGB can change 60p to 23,98p or whatever

.EDIT: My friend says, if you work for television, you are not to twiddle with the settings. Broadcast safe values were there for a reason.
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