Sunday, 6 November 2011

Lets do Astrophotography NOW! Part 6 Photoshop

At some point your going to start editing your photos and I thought it would be helpful to have a look at the process from start to finish using Deep Sky Stacker and Photoshop to edit your images.

There are many tutorial out there to help you with this but they all seem pretty scattered about so this series of tutorials will be kind to beginners and straight forward.

Lets do it in steps to follow the process.

STEP 1. Get your shots taken ready to load into deep sky stacker.
I pretty much cover this in parts 123 and 4 so read those first.

STEP 2. Put your shots through deep sky stacker its not hard I will leave you to get on with that.

STEP 3. Editing your stacked image in Photoshop.

OK this is the meat and potatoes of getting your image looking good. Lets begin with learning about the Histogram, Levels and Curves as you will need to learn these first.

This is the Histogram in Photoshop it will become your best friend so make sure you treat it nicely and pay attention to what its trying to tell you.

When you first open you stacked image in Photoshop your first port of call is normally Levels.
Go to Image-adjustment-levels and up pops your little levels box looking like this isn't it cute.

Any way all that black stuff is your data and when you first open a stacked image all that data is squeezed into the left hand side compressed like an elephant has sat on it. Your job is to stretch it all out being careful not to stretch it too much. A bit like blowing up a balloon but too much and it will go bang and end up being a mess.

So I normally start buy moving the gray slider arrow in the middle towards the left and keep adjusting the gray and black slider arrows until my data is nicely stretched across the histogram. Now this takes time and practice to get right but it is crucial for success. Think of it as unpacking your suitcase and laying the contents out in a good order ready to start sorting out your socks pants and trousers. There are many good tutorial out there on the net to help you understand the use of the Histogram and levels I will provide links at the end of this guide but for now lets just run through the order of things.

OK So having spent time learning about levels and the histogram you are now ready to move on to the use of the all powerful and mighty Curves tool it looks like this.

With out any doubt learning all about Curves and how to use them is going to be the crux of making or breaking your images. With the curves tool you can bring out all the fine detail of your images and control with very precise detail the areas of your image you want to work on.
But curves is also great for controlling colour as well as contrast in your images. So your next task is to go and find out all about curves and how to use them correctly. I will provide bunch of links to good tutorial at the end of this run through so dont worry.

Right then, having done your levels and curves while keeping a close eye on the histogram to avoid over stretching your ready to move on to the tricks of the trade as I like to think of them.

When I did my image of the Triangulum Galaxy or M33 it was a tough one as I did not have enough good data to get what I really wanted. But, I knew I had enough to get a reasonable image so after taking it through levels and spending a good deal of time carefully adjusting it in curves I was ready to apply the tricks of the trade.

And I ended up with this final image.

However when I first started in Photoshop this is what I had to work with..

As you can see your stacked image can leave you feeling you have come a cropper and failed but this is because you have to draw out all that detail in Photoshop with levels and curves. Once you start doing that the image becomes much nicer and full of detail.

SO Tricks of the Trade.

The use of layers and masks and blending modes.
Now these are brilliant for bringing out all kinds of detail and colour adjustment and I have slowly put myself together a note book full of the best ones I could find on the net from others that have come up with great solutions to common problems so let me share them with you..

Theres a lot of them so I may extend this into Part 7 8 and 9.

High Pass filter.

From my little note book one of the ones I love using is the HIGH PASS FILTER for bringing out detail in galaxy's. This one works great for images of M31 the andromeda galaxy and really helps bring out the detail on those tricky dust lanes.
Here is the image of M31 that this was used on for the dust lanes.

Here is what you do..
First of all you will need to duplicate your layer. In the layers palate right click your layer and select duplicate layer.

That done go to Filter-other-high pass and select a high pass filter of 5 to 8 pixels and press OK. Then change the blending mode to Over lay for that layer.

Good stuff hey your working with layers and blending modes. Now lets add a layer mask called a Hide All layer mask.

Go to Layer-Layer mask- Hide all

This will add a hide all layer mask to the new layer we are working on. In the picture below you can see the background layer which was our first layer. We duplicated that one to give us the layer above. Next we did the high pass filter and lastly we added the hide all layer which appears as that little black box next to our high pass filter. Notice there is a little chain between them. This chain links the two together click on it breaks the link and allows you to work just on the hide all layer. Leave it alone for now as we want them linked up and ready for the next stage.

Now we are going to paint the highpass filter detail on to the galaxys small fine areas. To do this we must first insure our foreground colours box is set right. This little box in the tool pallete looks like this you need to click the little bendy arrow to change it so that white is on top and black is behind. And remember that white reveals black conceals.
Next select your brush tool and choose a small soft brush to work with.

OK that done start to paint the high pass filter detail on to the dust lanes of the galaxy to bring out the fine detail. When doing this you can alter the opacity and flow of your brush if its too much. You can also apply a small Gaussian Blur to the mask to lessen the effect if you need to.

We now need to repeat all the above by first making another duplicate layer from our background layer. That done we use the high pass filter on it as we did before but this time we pump it right up to a radius of 40 to give us a coarse high pass filter for the outer dust lanes of the galaxy we also change the blend mode this time round from overlay the first one we used to soft light for this next one. Now using a slightly bigger brush we paint this coarse high pass filter on to those bigger dust lanes which will sharpen them up and bring out more detail.

At this stage its a good idea to switch those little eye icons on the layers your working on, on and off to see what your doing and how its going to effect your image.

When you are done your last job is to merge the layers down buy right clicking on the top one and selecting merge down then again and your done.

This is a great method for sharpening up those dust lanes and one I have used to great effect.

Here is the tutorial for it to add to your book marks. I suggest you get yourself a little Photoshop note book and write it all down in your notebook this way you will build up a good selection of useful tutorial as I have done that you can work from as you edit. Like me you will find that these great tutorials often disappear if a webpage goes down so keeping it all in a little note book will save you from that computers cant do everything just yet..

Thats if for this section next section I will pass on some more of the tricks of the trade tips for you to keep improving your images as we learn together if you like.

Here are some great tutorials on using the histogram levels and curves for you to book mark

Ok that little lot should get you started remember to keep a close eye on the histogram