Red Blocking

[MatthewRyan]

How do I keep reds from blocking when importing footage from my HD100? it happens in both HD and SD, more in SD though. The reds look fine played back through the camera but when improted they blocking in the red areas. It also only occurs on clips that have very little movement where there is no motion blurring. In some instances the blocking even occurs on other bright colors such as royal blue, orange, and vibrant yellows. anyone know how to fix this?

 

[Nate Weaver]

No way to do anything about it. It's a result of 4:1:1 or 4:2:0 color encoding on DV and HDV.

 

[J.R. Hudson]

Try and tame them using a Chromablur in your NLE and next time DON'T SHOOT RED !

 

[MatthewRyan]

Thanks guys. I have been trying to shoot as little red in my scenes as possible. In situations I can control there is no red but I can't help it if I'm shooting exterior scenes and theres red scattered around in the back ground.

 

[stephenlnoe]

Any way to post some raw stuff to see what your're seeing?

 

[MatthewRyan]

Here is one where even the bright colors on the uniforms of the soccer players, which are not red are blocking. The red tents ond the shirt of one of the players in the back ground are blocking.

<center>
<a href="http://i5.photobucket.com/albums/y180/skatefilmer18/90adb6f7.png" target="_blank">
<img src="http://i5.photobucket.com/albums/y180/skatefilmer18/th_90adb6f7.png"></a>**
</center>

 

[MatthewRyan]

hmmm that didn't work. lemme try it again

 

[MatthewRyan]

Maybe this one will

 

[MatthewRyan]

I can't manage to get the picture up in any larger size.

 

[Barry_Green]

Hard to tell at this size, but that looks like 4:2:0.

Look at Eleventy's comparison and see if you're seeing the color follow a similar pattern. Red against green will cause it to be most noticeable, or red against blue.
http://www.eleventy.org/dv-en/index.php?actie=resultaat

 

[MatthewRyan]

So basically colors that are opposite eachother on the color spectrum make the camera work harder and form blocking. This is what I'm getting from this. In my clips the blue and yellow, when together, block and the red and green, when together block.

 

[Barry_Green]

Well, the issue is that the same color gets assigned to a group of four pixels. HDV uses 4:2:0 color sampling, and that means that every 2x2 block of pixels are all set to the same color. Sounds preposterous, I know, but that's the way color sampling works. DV is the same way but different -- four pixels in a row (4x1) all get set to the same color.

The difference is in the brightness of the colors; each pixel in that 2x2 block can be a different luminance value, but all the same color. So you could have black-ish, white-ish, dark blue and bright blue all in the same block -- they're all technically shades of blue, so assigning "blue" to the block works fine, and the different brightness level lets us discern the individual pixels.

So what happens when you have four pixels in the source image that are different colors? They'll all get forced to be the same color. Let's say you had a 2x2 block and in that block there was a red pixel, a blue, a yellow, and a green. What would happen when that gets recorded? They all get turned to the same color -- in this case, probably some shade of brown. A big 2x2 block of brown. What if you had two blue pixels and two red pixels in the block? They'd all be forced to purple. Two yellow and two blue? They'd be forced to green. Three yellow and one red? They'd all be forced to yellowish-orange.

Now, if the brightness levels of each pixel are different, you'll still be able to discern four pixels there, even though they're all brown -- you'll see light brown and dark brown, etc. But if the pixels were all of comparable brightness, you'll just see one big ugly 2x2 block of brown.

So it's not necessarily that they're opposites on the color wheel, although that does contribute. What matters is if they're comparable brightness, and if there's no easy color to transition to. Let's say you had a transition from red to orange. That's easy -- red and orange are very similar, and if the pixels are of different brightness levels, it'll probably look just fine in 4:2:0. Won't look like a big block. Even if they're of comparable brightness, our eyes are fuzzy enough on color that red to orange probably won't look too bad at all.

But when the colors are opposites (like red and blue) there's no easy transition color between them. And if the pixels are of comparable brightness, you're going to get blocky blocks of color. No way to avoid it.

 

[WarrenS]

Looks like the red gain is extra high.

 

[MatthewRyan]

Barry, always a pleasure to read your posts. Thanks a lot.

As for the red gain, it was actually pretty low. I had turned it down when I got on location and those red tents were scattered throughout the back ground.