Nodes not rendering (can't see what's wrong) - HELP! ;-)


Hope someone can help. I am sure I am doing something stupid, but need another pair of eyes as I must be missing something.

Here is my node set-up (very simple) which shows some text with a glow effect.

However when i save the image, it does not give me the glow - just the text! - As evidenced by the preview in Mac OSX (10.6.4.) here:

This looks like the render rsult, without the nodes, so I must be doing something really simply stupid, but I can’t spot it - I will also try and post the blend. (posted see below)

The other issue I found, is that when importing the image to Final Cut Express (FCE), FCE does not always recognise the Alpha channel - although I have a suspicion these issues may be related.

Thanks in advance for your help.

Many Thanks



TEMP_PNG.blend (171 KB)

This is what I get when I press Render. Mac OSX 10.6.4 Blender 2.49b

Hi Richard

if you then press F3 and save the image as a png, does it save as you would expect - I.e with the glow in place and a transparent background? As it doesn’t when I save it - or at least I don’t think it does!



correct. the Glow area is just color, without alpha. Click and drag over the glowy area of the render and you will see that it has color, but A:0. So when you save it as premul or key, the color is saved, but the alpha is 0. Then when viewed, most viewer says that since it is alpha 0, it is blank, and thus nothing, nada, and the glow is wiped out.

What you want to do is to convert your color into a partial alpha value, so that other packages wont throw that color away by multiplying it by the alpha 0. To do that, insert the color ramp node with black (0) as alpha 0, but white as white alpha 1. then route the alpha channel from the color ramp to the composite output as shown. Now your partially white glowy areas will also have a corresponding alpha amount.


[gah! you beat me to the button!]


you could try feeding the output of your screen node into the alpha input of the composite node directly. You can use color correction to intensify or reduce your alpha.

More formally, one should take the screen output, convert it to black and white, and then feed it to the composite node. In this case you correct your alpha using math nodes. It works both ways in your case.

PapaSmurf and CubofJudahsLion

Many thanks for your help - works great!

Do you know if the existing 2.5 (alpha 2) works as well? As when I create the same image using 2.5, FCE seems to pick up as Straight Alpha instead of Premultiplied - even though I have selected Premultiplied in Blender.

I realise 2.5 is alpha so things could change, but wondered if anyone else had found this or something similar?

I will use 2.49 for the project I have at the moment as I know it works.

Many Thanks again guys