So I have rendered an Image Sequence and created a video of those images. Suddenly I realised that if I had only one image (shot by a camera or created with Blender) I would now go to Photoshop and do some colour correction (for instance set a white and a black point).
How best to do this with videos? Is it possible to color correct the whole Image Sequence in Blender or is that to be done in another software (like Adobe Premiere)?
Yes, you can do color correction in both the compositor, and in the color management tools of the Scene Tab.
I would use the Scene Tab option for Black and White, as it is pretty simple to do.
My recommendation would be to render one frame, get this set the way you like it in the UV/Image Editor, and then render your sequence.
Here's a look at the compositor (NOTE for just B&W adjustments, BrightContrast Node might be all you need). For rendering an existing Image Sequence change your Input to Image Sequence. If you want to influence color there is a Color Balance node just for this reason (although you could just play with grayscale values here as well). This is a huge topic, so this is not definitive, just a good starting point. You could use all sorts of things like color ramps, blurs, etc... to get the "LOOK" that you are going for.
If you find that you need to animate the color balance at any point in your timeline, you can keyframe any slider value by hovering your mouse over that value and hitting I as well.
Import your Image Sequence into the VSE and in the Properties Modifiers Panel with your Strip selected you can add a Strip Modifier for your whole Image Sequence like a Color Balance or a White Balance Modifier.
You could copy them to other Strips if needed selecting Replace or Append now since 2.77.
In the White Balance Modifier you can pick a Color from your Sequencer Preview to set a White Level:
All pixels will then mathematically be divided by this choosen color.
Apart from that, the Bright/Contrast Modifier might help you with the blacks. Or when you use a Curves Modifier, you can easily boost your black level when you lift the bottom left part of the curve:
Unfortunately, the Curves Modifier for Strips doesn't have the White and Black Level Color Choosers as the RGB Curves Node does - where you can set exactly what you want.
But this RGB Curves Node is only available in Compositing via Nodes. So You might consider using one of the VSE to Compositing Add-ons for this:
To use only nodes you might set your frame range to the length of your Image sequence, make sure, in the Post Processing Panel in your Properties' Render Tab you have only Compositing selected, check Use Nodes in the Compositing Node tree, remove the Render Layers Node and add an Input > Image Node instead. Set it to Image Sequence and set its frame range accordingly. Put the Color > RGB Curves Node between it and the Composite Node and hit Animation (F12).
(You might have to delete your default camera to prevent Blender rendering your Default Scene again and again, but I think it shouldn't do that when you delete that Render Output Node)
