Improvement on slideshow video quality
The article "Getting your video ready for compression, for playback on ipod, iphone and the web" is quite useful.
If
you did not pay attention to the quality of pictures and selected them
carefully, the generated slideshow video would be very blurry on
Youtube. Short transitions and black padding can
reduce the bitrate requirement for slideshow video, however, that's not
enough for good video quality on Youtube.
Cause of blurry picture in slideshow video on Youtube
There
are some important differences between common digital photos and
pictures in TV/Film, and it's these differences that lead to the
degradation of slideshow video quality on Youtube. .
- Most
digital photos (snapshots) taken by amateurs have a very large DOF
(depth of field). This 's the major difference between amateur digital
photos and TV/Film/Professional photos. A large DOF not only makes
the background distracting, but also makes the slideshow video contain
too many unnecessary details and be very hard to compress. This is
the major cause of video quality degradation on Youtube.
- For 25-30 fps video, the large DOF brings more flickering in "pan and zoom" of still images.
- Light is important for subjective video quality.
I
Workarounds:
- Image enhancement:
One possible solution is image enhancement before encoding. So far, I
've found that luminance enhancement did improve the subjective quality
of Youtube video greatly. As the luminance enhancement does not reduce
bitrate requirement., I guess that its effect is similar to light in
film, and is mainly an improvemnt in subject video quality.
- Use close-up shots rather
than medium or long shots. Closeups (e.g. human faces) tend to have a
high contrast and a low bitrate requirement. Usually, these pictures
are easy to compress in video. If you had to use medium or long shots,
please avoid photos with fine details. For example, a sunset picture
is much easier to compress than a picutre of tree and falling leaves
(fine details).
- Use photomontage.
In TV or film,
the distracting background can always be avoided with shallow DOF (35mm
film camera with long focal-length lens) or a controlled environment.
In slideshow video, you can use Photoshop to remove unnecessary
background and add a monochrome background instead. It can reduce the
bitrate requirement greatly.
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