Posted: Sun 18 May 2003, 11:27 Post subject: Compressing DV that contain photos results in flickering?
My DV video has many photo's taken by the photo button of my camera. When I convert my DV to mpeg2 with TMPGENC (2VBR mode, avg=6000, max=8000, min=2000), while all moving video scenes play perfect in a TV monitor, I have a serious problem with the fractions of the video where the photo's appear. That fractions have a very annoying flickering effect. Does anybody know the source of this? Is there any way to avoid it?
Thanks in Advance,
Joined: 04 Feb 2003 Posts: 587 Location: Lisboa, Portugal
Posted: Sun 18 May 2003, 15:36 Post subject:
There are three possible motives for this.
The first (unlikely) is there there are some very high-contrast, very fine details in the image. If some detail in the image is smaller than 2 pixels, it will only be in one of the fields, and when the interlaced image is displayed, it appears to flicker. The solution is to apply a "gaussian blur " filter to the area of the image that flickers. Use a strength (pixel diameter) between 0.3 and 0.7 for the filter. This will blur the detail enough for it to be on both fields.
The second applies only if you captured the still to a memory card, instead of to the tape. Some cameras use a different resolution when they capture to a memory stick (ex., 640x480 or 800x600). In this case, I would recommend exporting the frame to a good image editing program (ex., Photoshop, Paint Shop Pro, etc.) and resizing it to the correct video size (720x576 for PAL or 720x480 for NTSC), before importing it back into your editing program.
But the most common reason for this problem is much simpler: the camera (or the subject) was not perfectly still when you pressed the "photo" button. This makes the image in one video field different from the image in the other field, which can cause very noticeable flickering on the entire image. The "photo" button on video cameras can be a bit deceptive, and it's definitely not very useful. All it does is take the last video frame it recorded, and repeat it on the tape for 5 seconds. In other words, it's exactly the same as capturing (moving) video and applying a "freeze frame" filter in your editing program. Generally it's best to film normally and apply the freeze later, because that way you can pick a frame where everything was as still as possible (meaning both fields will have the same image). The solution is to apply a "deinterlace" filter to the photos. Most editing programs have this filter, and it renders pretty quickly. You will lose some detail (compared to a photo taken with everyting perfectly still), but it's better than cycling between two different fields.
Note: this flickering effect should also be visible on the DV original as long as you play it on a full-resolution video monitor or TV screen (it probably will not be visible on the camera's screen or on the computer screen, because those are not interlaced).
You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum