This blog outlines the differences between the various still and video file formats available with your Altair CMOS camera when using AltairCapture or SharpCap and other capture applications which support video.
Still image file formats (1 image frame per file):
The .FITS file format for Deepsky astrophotography:
.FITS Pros: Supports 8 bit and greater bit depths such as 12bit, 14bit and 16bit. Supports mono, colour and RAW images. Image data such as exposure and temperature is stored in the file header and all deepsky imaging applications read this data to help processing. SharpCap can load 16 bits of data from FITS files.
.FITS Cons: Can only be opened by a limited number of applications. Some applications require additional plugins to open this file type. File format is very complex and flexible, so files may display incorrectly in some applications and correctly in others.
The .PNG file format:
.PNG Pros: Can be loaded into almost any graphics application. Handles 8 to 16 bit bit depths and mono or colour images.
.PNG Cons: Many imaging applications may discard detail from 16 bit PNG files when loading them. RAW images saved in PNG will appear monochrome with a checkerboard pattern and may need additional manual settings in post-processing to ensure correct debayering. SharpCap can only re-load 8 bits of data from PNG files, even when loading 16 bit saved files.
Video file formats – used for high frame rate solar system stacking video, low light microscopy video etc.
The .AVI video file format:
.AVI Pros: Can be viewed in almost any video playback software. Can be uploaded to YouTube, or even better quality, Vimeo.
.AVI Cons: File format is complex and has many sub formats. Correct playback may depend on other software and codecs installed on the machine. Playback and processing errors may be subtle and difficult to solve. 8 bit only. Mono and RAW saved in AVI may appear upside down due to limitations of the file format. May not stack as well as .SER format due to compression artefacts. (Altair Cameras can be used to save RAW .AVI which is not compressed, so they are able to capture better quality video than say, a re-purposed webcam, Consumer DSLRs and camcorders which all compress video reducing the quality, therefore better for scientific imaging if .AVI format is required). We do not recommend using .AVI files for planetary or lunar imaging. Use .SER file format described below.
The “Scientific Grade” .SER Video file format:
.SER Pros: Uncompressed RAW video file format for highest possible quality. A simple file format with few variations – applications tend to work correctly with it or not at all. The .SER file is written with the Bayer pattern of the camera which simplifies post-processing for RAW captures. Supports bit depths of 8 bits per pixel and also up to 16bits. (therefore higher quality than .AVI or any other format for high bit depth scientific video. In fact every frame can be considered a full resolution 16bit image file). Each frame in the file is timestamped exactly. Supports Mono, RAW and RGB captures. .SER files tend to be smaller for the same amount of data than RAW .AVI at the same resolution and bit depth, and they tend to be captured to the hard drive or SSD drive more smoothly with less glitching because they do not rely on your PC hardware to compress them on-the-fly. This results in faster frame rates and smoother video. (It’s often best to start with .SER and convert to .AVI without any loss of resolution or colour data).
. SER Cons: Less post-processing applications support SER format so you need to convert it into .AVI using the free .SER Player app (but you can then select bit depth and so-on). Astronomy applications such as AutoStakkert AS2 (for stacking), Registax 5 and 6 (for stacking and wavelet sharpening), and PIPP (for preparing the video files for processing in the above), all accept .SER format directly. Interpretation of the .SER standard is somewhat different for each software, so sometimes you need to help the program to select the correct colour space if it doesn’t automatically recognise it (see our article on Debayering), but it’s usually no big deal as there are only 4 possible options to preview.