.fits LRGB & File Size

[04Stefan07]

Using a ZWO ASI178MM-Cool with LRGB filters. I was going over the data I captured and the red images look to be too bright (similar to the luminance channel). Is there a way to verify within the image properties what colour the monochrome image is? Want to make sure they weren’t captured using the luminance filter.

My images are normally around 13mb and noticed a few came out only 3.5mb. Possible corruption?

Thanks!

[vlaiv]

No way of knowing what filter is used unless it is written in metadata of the file.

Fits file format supports quite a bit of metadata information - observer, time, location, instrument and so on, and comments among other things. Software usually writes down useful information in this metadata and possibly even filter information although it can also be incorporated in file name (SGP for example does that).

Other than this, you can't tell what filter was used from raw monochromatic data unless you make certain assumptions - like comparing two channels on same known star and doing measurement of intensities (photometric data) and comparing that with expected values for that stellar type (from catalog) and particular camera model used and filter combination. Not easy thing to do, but possible with certain level of confidence.

Single sub from ASI178 will be 3096 * 2080 * 2 = 12879360 bytes of data and a bit more for header and metadata. If you have 3.5mb fits - then it is likely to be corrupt. Corrupt fits file will be easy to detect as fits internal structure specifies how long file needs to be. Any software that reads fits should throw an error if encounters invalid internal fits structure.

Could it be that image is written in another format like PNG or TIFF? These use compression and there is possibility to have valid data file containing full frame compressed to 3.5mb size.

Another option is use of ROI. Smaller size of image will result in smaller file size.

[04Stefan07]

Thanks for the reply mate.

I forgot to mention I was using SGP.

My images are normally 12,584 KB. I had 8 Reds only 3,150 KB which is really strange and are still .FITS.

I will go through all the data I captured and checl.

[04Stefan07]

OK so I worked out the sizing issue.

My reds were captured with 2x2 binning which is quite embarrasing. I must have accidently clicked the arrow to change it and didn't even notice. I was scratching my head thinking why he hell is it only the red channel lol.