Detail - Part I: Less is More
The top image is soft, and the second one is so sharp it almost seems dirty. Something isn't right here. Recently I've been noticing the extreme degree to which most video content has been over-sharpened. I had posted some frame grabs from a recent project on a message board. One of the comments I got was that the grabs had way too much sharpening applied. The ironic thing was, I hadn't sharpened the images at all. I took another look at the images, and sure enough. There were sharpening artifacts and ringing all over the place:
Click for larger. Over-sharpening is most evident in the texture on the cheeks, the left eye, and ringing around the right side of the face and shoulder. Note: if you can't initially see the artifacting, A/B it with a copy that has a .5 pixel Gaussian blur applied.
It was the result of in-camera detail settings. The more I looked at it, the more obvious it became, and I wondered how I hadn't seen this before. Then I started closely examining the video content I was consuming. What do you know... almost all of it exhibited the same problems. I was so used to seeing these problems on commercial content, that my eyes had gotten used to it.
Why are these artifacts undesirable? They trick the eye in to believing that the picture is sharper than it actually is. Isn't this a good thing? Perhaps for distribution. For some, the examples from commercial content posted above may have an acceptable amount of sharpening. However, there are a number of reasons why this extreme degree of sharpening should be avoided, especially in camera.
- Maintain maximum image flexibility for post - Sharpening should be done as one of the final steps in the post production process. Sure you can sharpen your image in camera, but once it's sharpened, you're stuck with any added artifacts. Say for example you're onlining your latest project, and realize that a shot is slightly out of focus. This can be fixed to a certain degree with sharpening. However, if you had detail levels turned up in camera, you end up sharpening existing sharpening artifacts, making them stand out even further. Better to do all sharpening post where you have more control, and can "undo" your sharpening by simply turning off an adjustment layer (or similar, depending on the onlining application of choice).
- In camera sharpening is generally inferior to what can be achieved later in the computer (unsharp mask, anyone?).
- More control over sharpening in the computer.
- Different deliverables require different amounts of sharpening. A theatrical release will require a different amount of sharpening than a DVD, which in turn, will require a different amount of sharpening than a web version of your film.
- Film doesn't do it - With most digital video cameras, we spend a huge amount of time and effort to get our images to "look like film." With film, what comes in though the lens is what ends up on the film. There's no fancy DSP to get in the way. Any sharpening that is done to film originated images is done in the DI. We should be doing the same with our digital cameras. Capture as pure an image as possible off of the chip. Do the processing in the computer, with a higher degree of control, and the ability to undo changes.
That's all well and good, but how do we control it? What settings do we use? The following analysis deals with Panasonic's HVX-200, but the principles apply to just about any camera.
The HVX-200 has several controls which deal with the detail and sharpening of the image. These settings can be found in the menu, under "Scene File Settings." The settings that we are concerned with are "Detail," "V Detail," and "Detail Coring."
This setting functions by actually drawing new elements in to your image wherever it detects an edge. For a good example of what this setting could do in an extreme case, take a look at the image from The Italian Job above. This setting is our biggest enemy. It has a value range of -7 to 7. It would seem that a setting of 0 would be the baseline. Any positive numbers would be adding sharpening, and a negative setting would add some sort of blur. Not so. By the time you get up to 0, a significant amount of sharpening is already being added to your image, adding an obscene amount of ringing. Positive values can look absolutely awful:
This image was shot with a Detail setting of -1. V Detail was set to -7, and Detail coring to -2:
There is even significant artifacting with detail levels set to -3:
Crop. FX element from The Inheritance. Click for larger.
It seems that the only way to get rid of the ringing is to set Detail to -7. Even then, in high contrast areas, there are subtle areas that still seem to exhibit small amounts of ringing. You really have to stress the image to see it, though.
We can try moving the Detail level up to -6, but even here, we can easily see ringing beginning.
3:1 crop. Click for larger. Levels and Hue/Sat. Unprocessed image here.
Set your detail level to -7, and keep it there!
V Detail is a lot more subtle than its evil cousin. This setting operates much differently on the image.
"Whereas DETAIL LEVEL works with edge enhancement, artificially drawing outlines around objects to accentuate their edges, V DETAIL LEVEL works with the existing image, accentuating vertical contrast between horizontal elements." -The DVX Book, p.51
This type of sharpening is especially evident in the second image from The Hire - Hostage above.
This setting also has a value range from -7 to +7. Again, the -7 value has no identifiable effect on the image:
As the value of the setting increases, naturally so does the effect it has on the image, namely the contrast of what the camera perceives to be "edges." By the time the value for this setting reaches 7, it becomes much easier to see what effect it is having on the image. You'll also notice artifacts really starting to show up, especially banding and the like, on smaller textures that the camera perceives as being edges.
In the two images below, you can really see the effects of the V Detail setting. Both were shot with Detail: +3, V Detail: 0, Detail Coring: +2
With this setting, you're probably safe to come up a few notches above -7 without having a noticeably deleterious effect on the image, but I'd recommend playing it safe, and dealing with it in post.
This setting acts on the noise in the image, applying a slight blur to what the camera thinks are noisy areas. One interesting thing to note is that on the HVX, this setting doesn't have the full -7 to 7 range of the previous two. It only goes down to -2. Given our settings above, this setting will have a very minimal effect on the image (see page 52 of the DVX book for an explanation of this). At higher levels, this setting can start to blur finely detailed areas of the image (hair, for example). Here we see it having a posterizing effect:
Use with extreme caution. It may not have much of a noticeable effect, but can really come back to bite you when you start pushing the image in post. Instead of trying to smooth the noise in camera, look into something like DE:Noise, an excellent noise reduction plugin that can achieve the same thing in the more flexible post-production environment.
Having read the above, you should now have a pretty good idea of how to get an optimally detailed (or un-detailed) image out of your camera. We still need to look into post production and see what to do with our new, sharpening free footage. There is more to come:
Part II: Balancing the Equation
Part III: Through the Ground Glass