One of the elements we can choose when we are going to perform a recording besides resolution, frame and so many others whether in cameras are video or DSLR 's is the compression ratio. These rates are independent of the issue of "Frame Rate", resolution and other items that involve the "video quality" issue. The lower the compression rate, the higher the density of information in the video will result in higher quality and possibilities in post-production.
The compression ratio is basically defined by some items: Luminance and Chrominance Amount and the "Frame Repetition" rate (Intraframe or Interframe).
These elements (Intra Frame or Inter Frame) were created to "facilitate" the possibility of creating videos. We must remember that each second of video has a variation of "frames" that can vary between 24, 30, 60, 120 etc. ... (depending of course the technical possibility of each equipment). If each frame received individually and in its entirety all the "information" that composes an image, it would practically be impracticable to create video size would be the density of the generated files.
These repetition rates can be basically defined in two ways:
Intraframe: This is a form where the frame construction uses the full extent of the image scan (low compression). In other words, although the file is being compressed (coded) each frame is constructed in order to preserve all the elements in its construction.
Example used by Canon cameras in the "ALL-I" compression mode that have file variation. In the figure below, it is possible to see that the image is generated "Frame a Frame".
Video Compression Rates
Interframe: In this process the files become less dense because there is a complex process of creating the image in the construction of each frame. Only a few "Frames" are created throughout their "sampling" (I). Some frames are created using the variation of previous and / or later frames in the video sequence (Usually the frames of the middle - B). Further frame sequences are generated by "predicting" the sequence of frames relative to their pixels.
Based on the comparison of the two figures using the compression ratio used by Canon (All and IPB) it can be observed that in the figure where the compression rate used was the IPB only from the change of the dots from three to four points is that a new frame was built in its entirety (Intra frame)
We found in most manufacturers the possibility of adjusting compression rates. These settings can be adjusted in the camera menus and each manufacturer usually presents these variations with different nomenclatures.
Canon DSLR Cameras: All and / or IPB
Sony Alpha Cameras: XAVC's, AVCDHD and MP4
Nikon DSLR Cameras: High and / or Standard.
Remembering that video cameras (Ex Camcorders) from several manufacturers also have this feature and their names also change between them.
In this way it is important to understand that:
If you want to do a good job of "Post production" in your video regarding color treatment, brightness, contrast, etc. .... Ideally, this material should be recorded under "low compression". This way you will have a greater breadth of manipulation of these elements. But remember that this recording format "consumes" a greater volume of space on your memory card and also in the editing process you will use more machine processing. In the case of Canon for example a low compression recording takes up approximately 3x more space on the memory card (In high compression mode on a 16gb card you can store 64 minutes of recording at Full HD resolution and recording at low compression you can only store 22 minutes in this same resolution).
If you need to record a large number of videos and have few media to store your work at the time of capture and your production does not require large "treatments" choose to record in "high compression" mode. Still you will have a good image and your work will certainly be well evaluated.
Always remember that regardless of the compression ratio, the good result of a video depends on several factors.
Posted on May 30, 2018 at 01:48 PM