Update: Please check out my new website myonlinedcp.com. It is the most convenient way to create a DCP. Simply paste a link to your film into a text field and receive a download link to your DCP 48 hours later.
A "Digital Cinema Package" (DCP) is the modern standard of digital cinema projection. It has replaced 35mm film. The main advantages over other digital container formats are that a DCP looks exactly the same in any DCI licensed cinema across the world and can display all the colors the human eye is able to see.
To create a DCP of your film for free you can download the open source software OpenDCP and follow my guide below. Please read it carefully, since small errors in the process lead to bigger errors during the projection.
The Apple ProRes video codecs have become quite popular for a range of applications. They are being used during editing, as intermediate codecs, for archiving purposes and as festival screening copies. Their greatest feature (next to the great image quality with acceptable file sizes) is that you can turn off "Automatic Gamma Correction" in the encoder settings. This means that image contrast and saturation will not change. Whereas most Quicktime Codecs will change your gamma! You might have noticed that your movs look different depending which operating system and software video player you use.
Currently there is no free and easy way to directly export a Quicktime with Apple ProRes on a Windows PC. Fortunately Avid offer their DNxHD Quicktime codec and others for free: http://avid.force.com/pkb/articles/en_US/Compatibility/en263545
Through my work for a film festival I have been coming across many films with a size of 1888 x 1062 pixels. This can happen when exporting 1080p films out of Final Cut Pro. To prevent this use Compressor for exporting your videos. In the "Encoder" tab of the compressor settings turn off "Add clean aperture information".