*** You'll probably want to download the (rather large) original 1080p file to see this effect.
It is well known that footage from the Canon EOS 5D Mark III benefits from sharpening in post. I have been adding some amount of sharpening to my 5D3 footage as part of my post workflow routine. However, I noticed some unpleasant artifacts around red (and orange) objects at their borders with other colors that is exaggerated by sharpening. It looked so bad with any amount of sharpening, that I couldn't take it. Not being an expert on such matters, I assume this is a result of color sub-sampling compression.
The issue I faced was whether I just leave any footage with red objects alone (unsharpened) or whether I could find a fix that would allow me to sharpen it without the ugly red artifacts. This actually works with any footage that shows these artifacts that are especially visible with red. While many may know this already, the following was a revelation to me, so I thought I'd share.
The trick is to add a slight amount of Chroma Blur prior to sharpening. I use Sony Vegas Pro, but I suspect any NLE has the chroma blur and sharpen filters. In Sony Vegas Pro 11, I apply a Sony Chroma Blur fx with Horizontal and Vertical each set to 0.500 pixels. Then, I apply sharpening as normal. The Chroma Blur smooths away the red artifacts without any negative effects elsewhere that I've been able to identify. The chroma blur even without sharpening is an improvement in my opinion.
So, I sat down to make a demonstration of this. Not being a Coke drinker myself, I made use of a bottle we had sitting around the house. Now, you'll probably watch this on Vimeo first and wonder, "What the heck is he talking about? I don't see any artifacts!" Well, at 720p, you probably won't. Download the 1080p file and you'll see it a bit better. Or not. Oddly enough, when I encoded this (even at 1080p) the artifacts were barely visible. They're clearly there on the timeline and there in the uncompressed render, but barely visible (virtually invisible at regular resolution) after encoding to .mp4 (using handbrake with no filters, by the way).
The best bet to see what I'm fixing is to look at the bottle cap at 0:32 and to look at the screen shots posted to the right. This is what it looks like on my timeline in the preview window and on the uncompressed output, except that it is everywhere on the red label, too. Oddly still, when I did a screen capture .jpg of these, they didn't show up clearly either. It seems that the compression algorithms serve to do a sort of chroma blur themselves. Only when I did a .png file at less compression can you see what I see on my preview and at higher bitrate encodes. I suspect you'll see it on your preview screen if you try this yourself with your own DSLR footage.
But, this all brings me to an odd conclusion (given that I've made and posted this video): I'm not sure I'm going to sweat this as much in the future, since the ugliness I see on my preview screen doesn't always make it to the end product after encoding. I take that back, I probably will, because I know it is there before the encode and I'll sleep better at night if I fix it using chroma blur. Anyway, I hope this helps someone else.
Camera: Canon EOS 5D Mark III
Lens: Zeiss 85mm 1.4
Picture Profile: Technicolor Cinestyle
Color Correction: Magic Bullet Looks (same adjustments made to all clips and no other filters or fx)
As usual, I'm interested in your feedback and thoughts on the matter. Has anyone else seen this on their timeline? Does anyone else have any methods for fixing it? Or, are there ill effects of chroma blur that I'm just not seeing on these shots?