[Kdenlive-devel] Blender cannot perform "flexible" resampling

[Gerhard Hübner]

> > The bad news: Blender downsamples every imported image to the selected
> > video resolution. When I zoom into an image using the transform effect,
> > Blender does NOT used the original image quality but just inflates the
> > pixels of the previously downsampled image!!! This ruins the whole
> > function and makes it practically useless. My big multi-megapixel-images
> > just get squeezed to nothing and then inflated into an ugly pixelated
> > mess. 
> 
> AFAIK this doesn't happens in blender, i.e. it doesn't downsample.
> You have problably set the render resolution to a low value. Furthermore
> if you have a low res image and you set resolution to HD, it can even do upsampling

I would not recommend to increase the video resolution as this results
in HUGE output files which have to be downsampled again to be burnt on
DVD or similar media. It could be done in a much much more efficient
fashion. Although the mathematics is really simple, it seems to require
an explanation:

1. The image resolution and the output resolution of the video are TWO
DIFFERENT THINGS!!!

2. Image resolution is usually greater than output resolution!

3. Therefore, when zooming into an image while watching the DVD video, I
want to see MORE DETAILS, not inflated pixels!!!!!

Example:

Let's say we have a picture with 2000x3000 pixels. I want to perform a
continuous zoom from factor 1 to factor 2 over 10 seconds. This means,
at factor 2, there are still 1000x1500 pixesl available, still much much
more than the DVD resolution!!! So, at zoom factor 1, 2000x3000 pixels
get downsampled to DVD resolution. While the zoom continues, a smaller
part of the image is selected and downsampled for each consecutive
frame. At the final frame of the zoom effect, 1000x1500 pixels are
downsampled to PAL. Therefore, throughout the whole zoom range from 1 to
2, the image is ALWAYS sharp and there is absolutely no need to create
huge output formats.

These would be the keyframe parameters during the 10-second zoom from
factor 1 to factor 2:

00 seconds: downsample from 2000x3000 to DVD
01 seconds: downsample from 1900x2850 to DVD
02 seconds: downsample from 1800x2700 to DVD
03 seconds: downsample from 1700x2550 to DVD
04 seconds: downsample from 1600x2400 to DVD
05 seconds: downsample from 1500x2250 to DVD
06 seconds: downsample from 1400x2100 to DVD
07 seconds: downsample from 1300x1950 to DVD
08 seconds: downsample from 1200x1800 to DVD
09 seconds: downsample from 1100x1650 to DVD
10 seconds: downsample from 1000x1500 to DVD

This isn't rocket science, is it?

Unfortunately, Blender is unable to do this simple kind of math. Blender
would depend on the output resolution being set to 1000x1500 and the
final video being downsampled again to DVD.

By the way, after fiddling around with Cinelerra, I found out that it
handles this kind of transformation smoothly without any problems. Seems
like it isn't as horrible as it felt initially...