The "Preferences" (PREFS) panel shown here is from an older version of HDLink, but the information contained herein is still up-to-date.
In the RED circle are shown the 5 quality options available when recording CineForm Intermediate files. Equivalent settings are also available when recording or rendering from NLE or compositing applications.
So the typical question is - "what setting should I use, and what will the resulting bit rate be"?
Background: CineForm files are coded using a VBR (variable bit rate) temporal Wavelet algorithm. This means as image statistics change (image motion, edges, texture, noise profile, etc) the bit rate goes up and down to compensate. Variable bit rate algorithms are also known as a constant-quality algorithms.
Based on the VBR nature of the algorithm, the resulting compressed file size will vary, for any given compression quality setting, based on the complexity of the image being coded. Obviously different frame sizes (spatial resolution) and frame rates also change data rates and file sizes.
As shown in the table there are 5 quality settings provided: Low, Medium, High, Film Scan, and Film Scan 2. On the Mac, CineForm quality levels are (currently) represented by a slider and percentage as shown in the table below. Also shown in the table are approximate data rates and file sizes for a given quality setting assuming source material is 10-bit 1920x1080 24p YUV.
Some Comments About the Table:
• CineForm 444 material will be about double the size of CineForm YUV material for a given frame size
• Certain applications don't exploit the temporal nature of the CineForm algorithm, and resulting YUV file sizes are approximately 25% larger than shown in the table. This doesn't impact visual quality, only compressed file size. These applications include Sony Vegas and Apple Final Cut Pro.
• Bottom Line: For most workhorse acquisition, post, and rendering uses we recommend either High or Film Scan. By the way, the background on the naming of "Film Scan" is that this mode was designed to accurately reproduce the characteristic of film grain during film scanning. So which one should you use? Experiment yourself - see if you can tell the difference.
By the way, our first feature film "Dust to Glory" used the High setting throughout post (we didn't have the FS modes at that time). The film prints for D2G were created directly from the "High" quality CineForm content on the Adobe Premiere Pro timeline and looked great!
• What about Film Scan 2? Internally we call FS2 "Overkill" - we don't use it very often ourselves. But it's there for a reason - you may want to consider using FS2 when you have very demanding post workflow requirements in which you are pushing or stretching the images a lot - a real lot. Otherwise FS1 and High are the best settings.
• What about Medium? For modest post manipulation of images Medium is fine and the image sizes are smaller.
For those that need smaller file sizes Low will work fine, although we generally don't recommend Low for content that will go through many generations of rendering.
When we performed the visual fidelity comparison of CineForm 444 versus the respected HDCam SR format we used both FS1 and FS2. As you can see from the diagrams, both quality selections exceeded the visual quality of HDCam SR.
Also for consideration: When selecting a higher quality setting (FS1 versus High for instance) the recorded files are larger. Be aware that files recorded using higher quality settings demand more CPU for real-time playback than the same file recorded at a lower quality setting. In case you care why...this is because larger files sizes require more entropy decoding (hence more CPU) than the same content recorded with a lower quality setting.