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GHS videos

Mike Cranfield
in PixInsight
Hi Adam

Thanks for the new GHS videos.  I would offer a couple of points that I hope will be useful:

  • The editing seems to have gone awry on the "Diving In" video - you seem to restart at around 1m 35s.
  • Also, just to clarify - the GHS process is not native to PixInsight - it must be downloaded from the https://www.ghsastro.co.uk/utilities/ repository just like the script.  If you have that repository in your repository list you will download both the script and the process.  I just thought it would be worth clarifying that as some people who have not added the ghsastro repository may be confused as to why they could not see the GHS process.

Thanks again for all your valuable work.

CS, Mike

Comments

  • BlockHeadBlockHead
    Thank you for your feedback Mike. I will adjust the content accordingly.

    -the Blockhead
  • BlockHeadBlockHead
    edited April 2023
    @Mike Cranfield

    When GHS encounters a real Gray scale image (a view that is of the "gray" type...which is a single channel image). Shouldn't the Color Options literally be *grayed" out? It seems odd to set the color mode to "Saturation" on a grayscale image and stretch it (among other variants).

    -the Blockhead
  • Mike Cranfield
    edited April 2023
    Hi Adam

    An interesting question!

    Let me explain the logic behind the current approach.

    GHS is intended to conform with the fundamental object oriented design philosophy of PixInsight.  So the GHS interface is first and foremost designed to define a generalised hyperbolic pixel intensity transformation that "exists" entirely independently of any image.  With the "track view" switched off, the multifunction display area has no histogram information but will still show the intensity transformation graph as that is intrinsic to the GHS that is being defined.

    Now, what should we do when a user decides to track a specific view.  If it's colour (or even color!) all parameters have relevance and there is no issue.  But if the image is greyscale (or even grayscale!), the colour mode parameters are not relevant.  Do we then grey them out, and thereby stop the user from being able to define them, simply because they happen to have "track view" enabled and are currently tracking a greyscale image? Or do we simply treat them as parameters that have no influence on how the transformation is applied to a greyscale image?

    We have chosen the latter approach for GHS. We do hide the colour options panel as that is not going to be relevant while a greyscale image is being tracked but it can still be revealed by the user if they so desire. 

    This is kind of analogous to what happens in Histogram Transformation.  In that process there is the ability to set R, G and B channel stretches independently.  If you track a greyscale image those buttons remain enabled and you can still specify individual channel stretches - they are simply ignored if you apply to a greyscale image.

    You could argue that if, for example, "Saturation" is selected then the GHS stretch is not relevant for a greyscale image and we should simply apply no transformation.  We would then rename the RGB mode to RGB/K and insist that the user selects that before they can apply to a greyscale image.  We didn't feel that was necessary and preferred the current approach as I have descriibed.

    So that is the logic for what happens at the moment, but always happy to hear alternative views - and open to be persuaded by them!

  • BlockHeadBlockHead
    I understand the logic...but I also understand you can't fight human behavior... ever!

    The reason for my question...is because I was asked this very question. "Should I be selecting RGB or Lightness in the Color Options for my luminance image..."

    On a personal level I am entirely agnostic... but when I see this question asked of me more than once..it raises my eyebrow. 

    I think my tipping balance is that I like the idea of have the Color Options grayed out when there is a grayscale image..there is something beautifully literal about it. 

    -the Blockhead
  • Mike Cranfield
    I agree that human behaviour provides a powerful rationale to do something else. I will give some more thought to the best approach. Thanks for your feedback.

    CS, Mike
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