Serif PhotoPlus tutorials - Adding a Luminance layer

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Adding a Luminance layer in PhotoPlus x4

If you are a PhotoPlus user and have tried following a PhotoShop tutorial for adding a luminance layer to your astro images, you may well have hit a fairly fundamental problem. Those tutorials rely on using a blend mode called Luminance in PhotoShop that doesn't exist in PhotoPlus x4. However, with a simple trick you can do exactly the same in PhotoPlus.

The theory

The Luminance blend mode in PhotoShop passes through the hue and saturation of the lower layer and the luminance of the upper layer. (If you need an explanation of layers go here). But PhotoPlus x4 doesn't have a blend mode called Luminance. What it does have is a blend mode called 'Colour' which works in the opposite way to the Luminance blend mode; in other words the result of the Colour blend mode is an image with the luminance of the lower layer and the hue and saturation of the upper layer. So to get the same effect as the Luminance blend mode you simply reverse the order of the layers! (My thanks to Angie Bowen for her explanation of PhotoShop blend modes).

Tutorial

So let's run through how this works. I'm using an image of M27, the Dumbell Nebula, for this tutorial.

You may have captured a seperate, detailed, Luminance channel for your image and you want to combine it with colour data. If not, a trick is to produce a false Luminance channel which, if you are using a mono CCD and filters, can be done by stacking all of your subs or you can simply produce a monochrome version of your colour image.

I am going to run through the process of producing a simple false Luminance using a monochrome version of a colour image.

Firstly, open your image (File -> Open) in PhotoPlus.

To generate a false Luminance from the same image, create a copy of the image (Edit -> Copy or Ctrl+C) and Paste As New Image (Edit -> Paste -> As New Image or Ctrl+V). This will appear as a new document, probably with the name Untitled1. Make this image monochrome by adding a Huw/Saturation/Lightness adjustment layer (Layers -> New Adjustment Layer -> Huw/Saturation/Lightness). In the dialogue box that appears move the Saturation slider all the way to the left or type -100 in the box. The image should now be monochrome. Flatten the image by merging all the layers (Layers -> Merge -> Merge All). This is your false Luminance.

If instead you are using a true Luminance layer then load that image (it will need to be the same dimensions as the colour image - I'm going to assume that it has been registered in your stacking software so that it matches the colour image).

So far this should be the same as a PhotoShop tutorial. But here is the difference: Make the colour version of the image active (by clicking on the thumbnail or selecting it from the Window tab) and copy the colour version (Edit -> Copy or Ctrl+C). Then select the (monochrome) Luminance version (again by clicking on the thumbnail or from the Window tab) and past the colour version as a new layer (Edit -> Paste -> As New Layer) of your Luminance image.

The colour image should be pasted as Layer 1 above the monochrome Background layer (in PhotoShop it would be the other way around with the monochrome Lunimance layer above the colour layer).

Then you simply change the layer blend mode from 'Normal' to 'Colour' and Robert is your mother's brother!

The image should have noticably brightened. If you are happy with the result you can flatten the resulting image (Layers -> Merge -> Merge All) and then save your result.

If you have any comments or questions then please do not reply to this thread but post them to the general PhotoPlus thread instead.