Hey everyone, my name is Mack Murdock here with OPT and it's been raining outside,
so in this video we're inside where it's nice and dry and we're going to be going over one
of the most basic and essential steps when it comes to processing your images - stretching.
When you first take your image you might see something that looks like this
where your target is barely even visible, but hidden under all the darkness
is the information you need to turn your image into this.
Stretching is taking the histogram of your image and literally stretching it so that tiny
sliver of data is scattered across the entire histogram, allowing you to see the shadows,
mid-tones and highlights that will eventually be in your final image.
There are different ways to stretch an image and no way is right or wrong.
We suggest you learn from a few people and find out which one works best for you.
We're going to keep it super basic in this video and show you how to stretch your image in
five different programs: Deep sky stacker, Photoshop, Pinxinsight, Affinity and Gimp.
But if you want to skip ahead to any of these specific programs
you can jump to these time stamps right here all right let's get started so the very first step.
And most essential step to stacking your image is right below this video you're going to see a
little thumbs up button hold your mouse over it until you see the sign says I like this,
and you want to ever so gently just single tap that button until it turns blue. After that,
hit the subscribe button and ring the bell for notifications
So our first program is Deep sky stacker, which unfortunately only works for Windows and this
is a Mac so luckily enough I'm a wizard so let's switch that out.
Alright let's get into it alright so this is Deep sky stacker.
So this is a perfect program to take all your calibration frames like your light frames,
dark frames, flat and bias - put them all into one program and have them spit out one image.
For you to start processing I normally wouldn't stretch an image in Deep sky stacker because
things like Photoshop or Pixinsight gives you a lot more control and fine tuning
However this is a perfect program to just be able to see what your image looks like
after you've done stacking them. So here is your histogram over here and your levels and
so I take the black slider over here and I move it until your data which is this part over here
is as stretched out as you can, so like right about there looks good and then you take your
middle slider your grays and you move it until it's right above this curve over here this curve.
And then finally you take the white slider and you just kind of stretch things a little bit more and
then you click apply and you should see an image come up and this is what the image looks like.
Alright, to save your image you want to click this over here save picture to file
let's call it uh North American nebula. Here it is
and uh to apply the stretched image you want to click apply adjustments to saved image over
here. If you would just like the raw stacked image you want to click this one over here. So
let's click this one and let's click save and that is how to stretch an image in Deep sky stacker.
Alright, so now that we're done with Deep sky stacker I want to switch back over to my Mac so
bbd bobbidy blue. All right well let's get into Photoshop. Alright so here we are in Photoshop
and here is our unstretched image, and now it's time to stretch it. So let's go to image
you want to go to mode and you just want to make sure the settings are in its right spot.
So if you're shooting in monochrome like I am you want to make sure that you're in grayscale
if you're shooting a color image you want to make sure that you're in RGB and uh you want
to make sure that you're editing in 16 bit. So the very first step that you want to do is go
hit the like button if you haven't already and then after that come down to adjustments and you
want to click levels and here you can see that the data in this image is all the way off to the left.
At that point what we want to do is we want to bring it a little bit more to the center and
start stretching it out so to do that you want to take this middle slider and move it closer to
where our data is and there you can see you know a little bit of our of our image and you click ok.
And so what we want to do next is go and just do it again and the reason why we want to do it again
is because now as you can see our data is closer to the middle and every time that you repeat this
process it's like fine tuning your stretch so we're going to move the black slider a little bit
and let's move this just a little bit as well and maybe just the whites a tad and then click ok.
And let's do that one last time. Ao adjustments levels something to keep in mind too is when
you're moving the black slider you don't want to move it over where your data is like
right about here uh you don't want to do that because what you're doing now
is you're doing what's called clipping and you're actually losing valuable information
so let's back off that area just a little bit right about there. Seems good to me. And uh
let's click ok and there is your nicely stretched image in Photoshop.
Alright let's head over to Pixinsight. So here we are in Pixinsight, the very first thing we
want to do is go to process and we want to open up two windows by going to intensity transformation
screen transfer function and let's leave that down there and let's go
to process intensity transformation again and finally go to histogram transformation.
So this first method is super simple on how to stretch your image and only done in like two three
steps so this button over here is for an auto stretch so you click it and here's our image auto
stretched and so the thing is is it's not applied to the image yet it's not applied to the histogram
it's just a preview of what it looks like so in order to apply it what we want to do is we want to
click over here which is the triangle and click that and drag it to the bottom of this window
and you can see here that you have this nice curve going and so at that point you click
this button over here to apply click the square and it's applied our changes
we see the white over here and all we have to do is reset our histogram by clicking these
reset buttons over here and one over here. And here's our image stretched out did it in three
clicks sounds good to me all right so the other way to do it let's open that up again is to use.
It's very similar to Photoshop in a way where you're moving the levels
so if you click the circle over here this will give us a real-time preview of our changes that
we're making. So here's our real-time preview and so you want to move the middle slider over here
over on the left and you should see your image start popping up just like that looks pretty good
as it is and then you want to click this button over here to apply and just like last time you
do have to reset it because it is still showing the same changes that you were making before.
So you click this button to reset and so far that's looking pretty good let's do it one
more time over here uh just a little bit and maybe bring down the blacks that's looking
pretty good and let's click apply let's reset and then finally let's just bring down the black.
Yeah so having that contrast really makes it pop
maybe we'll bring up the whites that's looking pretty good. Alright so let's uh let's apply
reset and click out of here and here is our nicely stretched image this method gives you
a little more control over how much you want to stretch it or what parts you want to stretch.
You can also take both methods and just combine them you can do the auto stretch and
then do the fine adjustments using the histogram transformation. Alright so now that we're done
with Pixinsight let's head over to Affinity. So here we are in Affinity and over here on the right
hand side you have all your tools like levels and gradient maps and your curves and so today for
just this section we're going to deal with levels and curves. So first let's head over to levels
click default we're going to move this gamma slider off to the left until you start seeing
your image so far that looks great. It's going to keep that about there and we're going to hit merge
and that saved that adjustment then we're going to hit default again and we're going to start moving
the black slider over and we're also going to hit it with the gamma, that looks good. Let's go black
again there you go you start seeing a little more contrast in your image and let's hit merge again
let's do it one more time so we're gonna hit default that's gonna bring that up start
bringing up this bring it with the blacks maybe just a little bit more there you go.
So far that looks great, now we're going to hit merge
and then the next thing we're going to do is we're going to head down to curves
we're going to hit default and we're going to give it a little bit of an s-curve so you want to click
down here bring that down and then we want to bring the highlights up give it a little more
contrast just like that hit merge - and there is stretching your image in Affinity
So the last one on our list is Gimp. Gimp is the only other free software besides Deep sky stacker
and this one is more geared towards editing. So let's jump on in so here we are in Gimp, here's
our image and so the first thing you want to do is go up to colors over here you want to hit at
levels and just like you know kind of the other programs you want to move the middle slider
about there looks good to me, you hit okay let's go colors again levels
and now you can move that black slider now that you've moved
your data away from the left hand side it's starting to come along.
That looks good maybe let's move this just a little bit as well, that looks good.
Click OK, do it one more time levels of the black slider that looks pretty good to me right there.
Let's click okay, we'll go color and now we want to hit curves and we're just going to do a basic
s curve so you bring the whites up and you bring the blacks down and this just
gives us a little more contrast in our image helps us. Let's do it one last time, curves
what's up bring this down so that looks like a pretty good stretch to me.
That's where I would keep it and at this point considering this is H-alpha data
I would do the same thing with S2 data and O3 data
and then just take those three images and combine them for a full color image.
So there you have it everyone you can see that there are a lot of similarities
between the different techniques in each of the programs, and again this is just
one way of stretching your images. You can mix and match what you've learned in this video with
other techniques to bring out the most out of your data. Let us know in the comments which program
you use to process your data in a future video, we'll dive a little bit deeper on more advanced
ways of stretching and processing like using star mass and setting your white and black points.
Feel free to check out the link in the description
below to download some free raw data for you to mess around with.
If you guys like this video and found it helpful, please hit the like button,
subscribe and ring the bell for notifications.
My name is Matt Murdock here with OPT, and we'll see you in the next one!
Clear Skies!