Monday, 7 November 2011

Lets do Astrophotography NOW! Part 7 Photoshop

Back again for some more tricks of the trade in Photoshop
In Part 6 we looked at Histograms Levels and Curves and I trust you started keeping those book marks and a note book as you learn these methods.

In this part I would like to look at Layers and layer masks and the inverted layer mask but before we get started lets use our imagination...

Imagine you are a window cleaner and you are cleaning a very grimy window. Your inside and it was horrible weather out side so who can blame you. As you clean the window removing the black grim with your white duster you reveal a lovely sunny day out side. Great you think I will get this done and knock off early, but wait suddenly you see your old enemy coming down the pathway. You quickly change your white duster to the black dirty one and grim up the window again but with the white duster you clean two spy holes for your eyes to make sure he doesn't steal your ladder.

Using Layers in Photoshop is like being a window cleaner so remember this visual aid to help you out as we make a start.

First lets look at the layers palette

You will be using this a lot so lets get used to it and understand it.

Number 1 in the picture is used to create a new blank layer, however most of the time you will simply drag your background layer onto this little icon and create a duplicate layer of your background image. You can also right click on the back ground layer and select duplicate layer if you like but dragging it onto the icon is faster I find.

Number 2 creates a new layer set but you wont be using it so ignore for now please.

Number 3 Creates an adjustment layer, you will be using it but not in this section.

Number 4 This is the one we need to look at closely as it will create our Layer masks for us.
Pressing it once will create a white layer mask called a reveal all layer mask. Pressing it again while holding down the alt key will give you a black layer mask called a hide all layer mask.

Now remember the old saying.. WHITE REVEALS AND BLACK CONCEALS.

SO when you create a white layer mask on your duplicate layer it will reveal the image just like having a very clean window to look through. If you use a black layer mask it will conceal everything like having a grimy dirty black window.

How is this going to be useful to you as you work on your images?

Well many times we need to change the the colour of parts of our image or we might need to apply saturation to the galaxy with out saturation effecting other parts. We might want to boost colour on one area and leave it off other areas. All this and more can be done with layer masks.

Now I could bore you to death but instead I want you now to go and take a look at this brilliant tutorial on using layer masks. Get your note book out and book mark this tutorial for future reference because if it goes off line you will be coming back to me and asking me for my notes.

Here is the tutorial its really good and you will love using layer masks go through it several time so you really understand it.

After you have practiced some more with levels, curves, high pass filter AND layer masks, we will take a look at the very helpful if somewhat confusing


The inverted layer mask is useful for getting rid of noise and graduation in your images here is how it works.

You create a duplicate layer of your background layer.

You then go back to your background layer click on it to make it active and press Ctrl A then
ctrl C to copy it. This selects and then copy's the background layer.

Having copied the background layer you go back to the duplicate layer and click on it to make it the active layer again

Now using your new found skills from above you create a white reveal all layer that will appear next to your image in the duplicate layer.

SO far so good.

Ok now we need to press the alt key and click on the white reveal all layer and then we hit ctrl V to paste our back ground layer into it.

Good, Now we will invert this image by hitting ctrl and I this will invert the image for you.

Now you should have a negative of the background image. Sticking with it we use levels to bring the white parts up and darken the areas we want to keep like the galaxy for instance remember white reveals and black conceals!

Now we have done that we have one last magic button to work on and that is found in number 5 the layer blending modes. You need to change this to soft light and then adjust the opacity slider down a bit. Make sure you select your image in the duplicate layer before doing this if you keep the white layer mask selected it wont do anything.

Well done now all you have to do is merge that duplicate layer down right click merge down and your done.

The invert Layer mask is very useful for getting rid of gradients and noise but its sometimes needs more than that so we will cover that in the next part along with selecting stars and reducing stars.

Here is a great tutorial on using the inverted layer mask method. Get that note book out !

Vavoom your Zoom!
Also one really helpful tip I picked up recently that saves you a lot of zooming back and forth is to go to your preferences in Photoshop Edit-preferences-general and make sure to tick the box that says zoom with scroll wheel. This will enable you to zoom in and out on your image with your mouse wheel much faster and a real time saver!