Bryan's Single Chip DLP Artifact Page
These images are an attempt to document what certain artifacts unique to single chip DLP systems look like. I'll be adding more images and/or improved images as I discover ways to document different artifacts.
The Rainbow Effect
The following is the best example of the "rainbow effect" I've been able to capture. In my experience, it is most easily experienced when the image has bright, well defined, thin lines on dark backgrounds, and by my estimation, is caused by the way DLP "stacks" the red, green and blue components of light over a period of time.
This is the circle from the aspect ratio check found on the THX Optimizer which can be found on just about any THX certified DVD. On this particular image, I can see the rainbow effect by moving my eyes back and forth across the screen. I have simulated this by setting my camera's shutter speed to 1/15", and shaking it back and forth quickly. The bottom portion of the image is the white circle as it would appear during normal viewing.
As you can see in the enlarged version of the image (click the image above to see the larger version), it's not really a full "rainbow" so much as it is a separation of the red, green and blue components of white light. During normal viewing, the rainbow effect is as people have been describing it, a fleeting phenomenon. It's gone before you even really realize it was there. In my opinion, it's not nearly as bad of a problem as some people have been making it out to be, and it certainly does not make the image "unwatchable".
I should note however, that this effect seems to affect different people in different ways. Some people can see it more easily than others, and other people cannot see it at all.
Temporal dithering is something that most often occurs when you see video with a medium to fast speed pan. There are many theories as to exactly why it happens, but it is not an MPEG artifact, as it goes away when you pause the image, suggesting that it only happens while an image is in motion and is not something that is stored in the original source like a compression artifact.
Temporal dithering has proven to be a difficult thing to capture as a still image. I need to use a fast enough shutter speed so as to not capture more than one frame of video, which makes it difficult to capture enough light to get a decent image, but this, so far, is the best I have been able to come up with.
This is from chapter 27 of the Monsters, Inc. DVD. The top section is the overall frame, with the DVD "paused" (actually, I used the "still" button on the Samsung remote to freeze the image), shot at 1/60th of a second (which is why it is somewhat dimmer than it would actually look on screen). The bottom left is an enlarged section of the paused image. The bottom right was shot at 1/60th of a second with the DVD actually playing, and the yellow bar moving somewhat quickly across the frame. You can see that the transitions between different shades of yellow are not as smooth.
Temporal dithering looks similar to color banding or gradient stepping (or any number of other names people have given to the same phenomenon), except the edges of the color bands seem to dance, and as I mentioned before, it only happens when something is moving across the screen at medium to high speed.
I admit, this is not the best depiction of the phenomenon, but it's the best I've been able to come up with so far.
The Clay Face / Color Banding Effect
I've decided not to cover this "DLP artifact" for now, as I rarely, if ever, experience this effect on any input source other than DVD, and even then, not on every DVD. I'm fairly convinced that the majority of the time people experience this effect it is due to poor source material, which is why I am not covering it..
That's the end for now. I'll be documenting more DLP artifacts as I am able to collect them.
Last Updated February 8, 2003