V2.2.0 Release Notes


This note covers the following features introduced in GHS Version 2.2.0.

Preview readout controls

Readout view:

Readout statistics are calculated on the target view before application of any specified transformation and based on actual pixel values in the target image (not resampled pixel values in the preview image).  The pixels used to calculate the readout statistic are specified alongside the heading “Readout:” in the readout controls area.

Readout reticle:

The readout statistic is calculated for the area within the square indicated in the readout reticle on the preview image.   The reticle can be placed by clicking on the preview image.  It can be moved by click and dragging.  The readout area can be altered using the “Readout size” slider in the readout controls. Setting the readout size to zero will give readout statistics at the selected point.

The readout reticle may be shown or hidden, while retaining the underlying readout values, using the “Show reticle” checkbox at top right of the readout controls area.

Readout statistics:

The following readout statistics are available: mean; median, maximum and minimum.  These can be selected from the dropdown to the left of the readout controls area.

Readout channels:

The readout channels available depend upon the channel selection option (buttons below the histogram plot) as follows:

Channel selection option

Available channels

Default channel


Red; Green; Blue; RGB/K



Red; Green; Blue; RGB/K



Red; Green; Blue; RGB/K



Red; Green; Blue; RGB/K











Where more than one readout channel is available these can be selected from the dropdown to the left of the readout controls area.

Readout reset:

The reset button (left pointing “x”) in the readout area will clear all current readout statistics and remove (not just hide) the reticle from the preview image.

Readout histogram link:

The readout value can be displayed on the histogram using the checkbox “Show on histogram” in the readout area.  A vertical line will show the readout value on the histogram.  The colour of this line can be altered as preferred in the Preferences Dialog (spanner icon at bottom right of the main dialog).

Readout parameter link:

For relevant transformation types, the readout statistic can be transferred to set the value of a relevant parameter using the “Send value to …” button to the right of the readout controls area.  The function of this button will alter depending upon the chosen transformation type as follows:

Transformation type

Button function

Generalised Hyperbolic Stretch

Send value to SP

Histogram Transformation

Send value to SP

Arcsinh Stretch

Send value to SP

Linear Stretch

Send value to BP

Image Inversion

Send unavailable

Image Blend

Send unavailable

STF Transformation

Send unavailable

Parameter/histogram linking

In Version 2.1.0 the reset buttons to the right of the parameter input sliders doubled up as a means of transferring the histogram selected readout value to that parameter.  This functionality has been removed from Version 2.2.0 as the new functionality described below has replaced it.

Parameter reset buttons:

These buttons (the left pointing “x” on a black background) will now always reset the associated parameter to its default value.

Histogram parameter link button:

This button, which is found just below the “Log view” button under the histogram, works the same way as the preview readout parameter link button described above, but by reference to the histogram readout value.  Note, by default the histogram and preview readout values are indicated on the histogram with different colour lines (you can change the colours of these lines in the Preferences Dialog, but we don’t recommend changing them to the same colour!)

Parameter/histogram link buttons:

The parameter/histogram link buttons are not enabled by default.  This is because users may feel the histogram/parameter link button described above meets their requirements. 

To enable the parameter/histogram link buttons you will need to check the “Enable parameter/histogram linking” option in the Preferences Dialog (spanner icon at bottom right of the main dialog).

Once enabled, clicking these buttons (the left pointing “x” on a light background) will transfer the selected histogram readout point value (if any) to the relevant parameter. 

You can also hard link this function by shift-click on the button.  This will turn the button to the link symbol.  In this mode every change in the histogram readout value will be reflected in the relevant parameter (and vice versa if you change the parameter value).  This avoids moving the mouse back and forth from the histogram to the transformation parameters panel when testing different values. You can release the hard link by clicking on the button again.  The hard link is also released if you change transformation type.

Note that LP will always be constrained so it is never greater than SP.  Also, HP will be constrained so it is never less than SP.  The value of SP will not be constrained by LP or HP, but the values of LP or HP will be adjusted to accommodate SP if necessary.

Other changes

Image Inspector:

The Image Inspector dialog remains available in the same form as in Version 2.1.0. However, the button to launch it has been moved from its previous location alongside the target view selector, to its new location in the preview controls.

Although much of the functionality of the Image inspector is now available directly on the preview, the Image Inspector does provide some additional functionality.  This includes pixel values after application of the transformation as well as key histogram statistics on the post transformation image.

Zoom and pan controls:

Buttons have been added to allow one click zoom to max, as well as one click pan far right.

Log histogram view:

The previous graph icon that toggled between a log histogram and a standard histogram has been replaced by a text button to make its function clearer.

Zoom histogram performance enhancement:

Performance has been improved when the histogram is zoomed to a high magnification.

Miscellaneous edits/fixes:

Other miscellaneous edits and fixes have been made. 

Bug reports:

If you encounter any bugs then please let us know via email to bugreport@ghsastro.co.uk.  Please do not use this email for more general enquiries about the script as these are better posted on the forums (eg Pixinsight, Astrobin, Cloudy Nights, Stargazers lounge etc) where you will have access to the much wider knowledge base of other users.