Colour correction for rubbish projectors – Part 1

Hey – don’t all die of fright, but I’m posting a new post here again.

I won’t bore you with a detailed explanation, but suffice to say that a young family and a new job in a different city, house sale, purchase, rennovation etc. etc. meant that VLOBLIVE posts weren’t high enough up my priority list to surface for a long time.

Anyway – enough excuses –  how about a post, you all say…

Well I was finishing off a video for showing in a Church today and the church in question had a rather limited video projector – I think it’s around 2000 ANSI lumens and it doesn’t cope too well in strong sunlight.

I was thinking how to colour correct for this and thought I would note down my musings here.

This first post concentrates on preparation…

Here’s some tips…

1. Know your enemy.

If you haven’t already you should have projected my greyscale brightness chart and adjusted it to get the best compromise (and it will always be a compromise) between seeing all the black bars and getting the whites as white as possible but still distinguishing the bars.

Here’s a reminder of the chart

 

grayscale ramp in 20 steps

grayscale ramp in 20 steps

 

 

Here’s what the grayscale chart SHOULD Look like on a waveform monitor in FCP

 

Waveform showing grayscale ramp

Waveform showing grayscale ramp

 

 

What you will probably find is that if you push the whites up to a sensible level, then you will start to lose the distinction between the black bars. This is because LCD projectors are rather bad at producing true black and you are fighting against ambient light to get a true black on the screen.

So here’s what you would actually see on the projector

 

crushed grayscale

crushed grayscale

Notice how all the black bars are crushed down to the same black level (on a projector it would be gray not black)

This would mean that instead of trying to get the blacks down to 0, you may have to bring all blacks UP to, say 20% just to make them visible.

 

(Remember to do this test under the SAME light levels that the final piece will be displayed)

Once you’ve done this you will know how much of a contrast range you have to play with.

If you lose the last two bars of black, that means there’s no point putting any detail in that range, as no-one will see it. Try correcting the brightness bars graphic itself until you can see everything and then use those values as your base level for all other correction.

If there is any way to actually monitor ON the projector to be used, then that is ideal, as then you can correct to the exact requirements.

Failing that if you can adjust your preview monitor in your edit suite to give a similar response to the projector, that’s a reasonable compromise.

Alternatively do a test piece when you have some downtime – take a clip you know well and apply some different correction ranges and add titles to tell you what you did. Then play it back on the projector and take notes (‘that wasn’t enough saturation…that’s still too dark in the greys’ etc.)

 

2. Use a good tool.

Just to mention that I’ve started using the Apple Colour program for colour correction and image adjustment. I used to use the 3 way colour corrector in Final Cut Pro, and that works pretty well for most things and for a quick fix while editing, but I was always a bit dissapointed with the end result, especially when editing in HDV with limited colourspace (4:2:0)

I had shied away from Color as it seemed a bit scary, but having gone through some web tutorials at Kenstone,net  LAFCPUG etc. it’s acutally pretty straightforward to use and to my mind produces a MUCH nicer result. It’s not that it does anything radically different, it’s just that it seems you can really push the grading to extremes and it holds up far longer than it would in FCP. This lets you recover really bad clips which would have looked really dodgy before.

Some warnings about using Color that I discovered to my cost.

 

  • Read the ‘preparing media for color’ section in the user manual. There are some things that really trip it up. For example I modified my FCP project to have a single video track (just by dragging clips down, while holding the shift key), and you have to ‘bake in’ any speed effects, otherwise it tries to correct the WHOLE original clip, which takes ages.
  • Rendering is S L O W. You thought FCP took a long time to render. I’m on a Dual 2.7G Powermac and it literally took overnight to render a 12min clip. So don’t expect to do this in a hurry. UPDATE – you REALLY want to be running Color on OSX 10.5 – rendering is MUCH faster – go figure!
  • Do everything else BEFORE you do the colour correction. You can round-trip with Color and FCP,but it’s probably safer to make it the VERY last step.
  • for HDV It’s particularly important to set color NOT to render in HDV but to use ProRes422 instead. This will let it use a much wider colourspace and give better results. There’s a great tutorial here that tells you all about this. If you’re doing HDV you want to use option 3. Basically the trick is import HDV, render to ProRes and export back to FCP as a ProRes sequence NOT an HDV sequence.
If you don’t have access to Colour, then FCP has good colour correction tools, as do the Avid NLEs and Premiere Pro (I think).
Even the good old iMovie08 now has perfectly usable colour adjustment tools, so there’s no excuse not to tweak your clips to look their best.
3. Remember colour correction doesn’t have to be about colour!
A big part of the process here is about brightness correction and distribution and nothing to do with the colour of the clip. You are trying to maximise the dynamic range of the clip within the constraints of the display setup it will be shown on. So you want white things to be white, and black things to be black and any detail hidden in the dark grays and the nearly whites to be visible.
This means adjusting the brightness, gamma and clipping of the clip before you even touch any colour adustment. To give you an idea, I adjust brightness on almost EVERY clip, but might only adjust colour on 1 or 2 clips in a whole piece (unless someone’s set the white balance wrong while filming!!)
4. Be subtle
Just like any other digital effect it’s REALLY easy to over-cook colour and brightness adjustments, especially when you are new to it. If you ever watch a real colourist at work, it’s really hard to tell what they are doing sometimes as they are making such subtle adjustments.
Best approach is to make an adjustment until you see the results and then ask ‘how far can I back this off, and still get the desired result?’.
OK, that’s all for now – I hear some small feet moving around upstairs so better go.
Can’t promise lots of posts, but I’ll try to keep this alive.
I’ll try to do a part 2 which shows some actual examples of the type of correction you could make.
Dave
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One Response to Colour correction for rubbish projectors – Part 1

  1. Anthony says:

    Wonderful! A new blog post. It seems that many people have shied away from your site as it was left un-attended for most of the year. Please do keep posting, and helping us with our endeavor to do great video 🙂

    This blog could be extra important for some as we lead up to the BIG Christmas productions this year.

    Anthony.

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