The resulting HDR image is extremely dark, as expected. It is a linear image with a huge dynamic range (the whole range of the M42/M43 region) stored in a numeric range of at least 230 discrete sample values. Note that this HDR image does not fit into a 32-bit floating point image, where you can store a maximum of about 224 discrete values. This HDR image requires either the 32-bit unsigned integer format or the 64-bit floating point format, both available in PixInsight. The HDRComposition tool generates 64-bit floating point images by default, although 32-bit floating point can also be used as an option suitable for moderately large HDR compositions.Here is the HDR image with an automatic STF applied. STFs are 16-bit look-up tables in PixInsight. Note that a 16-bit LUT causes posterization in the screen representation of this image. There is no surprise here, since as noted this is a 64-bit floating point image storing more than 230 discrete values.