Channel HMII

Sun (and sunspots) in visible light... These images are from HMI telescope on SDO, the abbreviation HMII (probably) means HMI Intensitygram, also called "continuum"...

The recent ones are jpegs from NASA / GSFC website, available daily, while the older months are generated from 2K fits files downloaded from JSOC few days after end of the month, in 3-hour step... (I didn't find 2K fits files on JSOC website, probably they are not there, but they can be acquired by Export Data form and the api thereof...)

Courtesy of NASA/SDO and the AIA and HMI science teams.

When comparing these HMI images (either intensitygrams or magnetograms) with EUV images from AIA telescope, the HMI images need to be resized 1.008/1.199 = 84.07% while keeping same center...

When generating these images from floating-point data, I use the following formula:

var F:=LoadFitsNorm(FitsFile), w:=F.Width, h:=F.Height, B:=NBm(w,h);
F.Scale(1/65535);
F.IntGamma(-64);
B.CombineHsl(22/0xff,1,F);

Gamma-corrected values are written into Light channel, Hue 22 / 255, Saturation 1 ...

NASA jpegs use probably little different colormap...

For counting sunspots, it is better to use HMIIF format, which is HMII flattened... (I will describe the flattening method I use sometimes later... NASA also publishes HMIIF flat images...) 

Compare the difference:

HMIIF flattened:


HMII from Fits, Hue 22:


HMIIC jpeg from SDO GSFC NASA web-site :


Available in Heliograf since 2023-11-13 , images now since start of 2023, older years may be added sometimes later, when space on web-site permits...