Hello,

I have calculated a number of .png files using imagemagick.
In gimp the files look splendid, but when inserting them as a clip in kdenlive,
the graphics look jagged (no anti-aliasing?).

Are there any limitations in rendering images like this?
Or what could I be doing wrongly?

Best regards,
Stefaan Himpe.

For the best result you should use same image size as video! And for size use "composite" transition and size = original, then all should be the same as original image!

Hello, and thank you for answering.

If you say: "same size as video" do you mean the size of the default profile?
(i.e. 1920x1080 here, though I don't use actual video footage this time)
or the size of what i render to (i.e. youtube 640x480)?

Actually, I tried both and neither gives an acceptable end result.

Then I thought: perhaps, when loading a .png file as clip, kdenlive already scales it to match the default profile size,
and then when rendering, the already scaled clip is rescaled again to the target size?
That might explain the loss of quality. I tested this out by creating a profile with default size 640x480 (in combination with using images of size 640x480 and rendering to 640x480) but
it didn't improve the quality.

Also: why do i need composite? there's nothing else besides these clips, and never more than one is to be visible at any given time, (so e.g. there also no video to mix them with).

I have added two screenshots which hopefully illustrate the problem more clearly.
I have also added the original .png file in case you want to try out for yourself
(if you dont' find it, it's because it consists of white text on transparent background :) )

Any further insights in this matter are appreciated.

Yeah! For me the same result with your image! :/ still testing now...

some resoults:

project was HD 1080p 23,9 Hz

1.test - sample image 720p: http://img690.imageshack.us/img690/4413/720pimage.png (text on the top is on the empty alpha ch.) [quality = OK]
result when I rander it to MPEG-2 (25000k) resize to 720p , screen: http://img692.imageshack.us/img692/7374/720p.png [quality= bad.. ]

2.test sample image 1080p: http://img17.imageshack.us/img17/4396/1080pimage.png [quality = OK]
result when rander ir in MPEG-2 (25000k) size = 1080, screen: http://img189.imageshack.us/img189/7493/1080py.jpg (saved to 100% quality in jpg) [quality=OK]

I don't know why it randers in 720p in so bad quality, but for 1080 it's more better, strage....

Upon further investigation, my .png file contains partially transparent pixels.

Perhaps this is not supported by the libraries used by kdenlive?

It seems that the picture, after importing in kdenlive,
is showing the partially transparent pixels as fully opaque leading to the ugly results.

Yes! Yes! YES!
The transparency was causing the trouble.
I've rerendered my .png files without transparency effects
(using grayscale for anti-aliasing) and now after rendering it looks very slick!

Yes, the "partial transparency" aka alpha in PNG is supported, but it does not "pass through." Alpha is only used when you composite the image over another image or video. The simple solution is to put these on the bottom video track and add a composite transition to them, resized to the entire duration of the clip. This will composite the images over the hidden "black" track. If the bottom track does not work, you can still add a Composite, but in the "with track" drop-down at the top of the Transition panel, choose "Black."

Yes :) if there is no video under image, that transition "composite" and with track "black" it works fine :)

For me, image files looks better if it is put into a title clip.

Cheers.