when i render something, as image or video, is there any option to change the contrast or saturation of the image without having to use any external software?
Thanks in regards.
An often overlooked feature is blender's colour management options that can be found in the scene properties.
If the simple exposure and gamma controls aren't enough you can enable Use Curves to get more control.
The compositor has a whole section of nodes for image control.
To use the compositor open the Node Editor window and set it to compositing mode:
There are nodes for brightness contrast and hue/saturation:
On top of that there are nodes for levels, color correction, curves and other ways to affect a rendered image.
Quoting from the wiki:
These nodes play with the colors in the image. They adjust the image's color intensity, adjust contrast and intensity, and, most importantly, mix two images together by color, transparency, or distance.
For an in depth explanation on each one of those nodes refer to Manual