In this video we're going to edit my
image of NGC 7000 the North America nebula using GIMP. How's it going
everybody, Ruzzy here for AstroFarsography. so go on down to the description below to
download the data of the North America nebula to edit along with me and while
you down if you want more reviews, how-tos and vlogs for all things astrophotography
make sure to subscribe and hit that bell notification so you never
miss an upload. So now you've got the data I'll see you in a moment in GIMP
ready to edit.Okay now that you've opened the picture into GIMP you're gonna see
something like this and that is because Deep Sky Stacker applies no stretch or
editing to the photo as it's out of stacking we have to do all that
ourselves.The only thing I've done to this picture so far is resize it to
1920 x 1293 because the original files like five
thousand 5000 pixels big and GIMP does not like handling it. Well it can handle it
but it just takes ages. SO I've resized it for the tutorial so
to begin editing we need to start seeing stuff so we're going to go to 'Colours' and
'Levels'. 'Levels' allows you to adjust the Black, Gray and White points of an image,
and we need to stretch the signal so we're going to move the white point of
this image down to stretch and amplify the signal that's there. So we can start
seeing stars appear I'm gonna do that a second time because doing it twice
gives you more control. If you're all the way down here you don't have a lot of
control each, little movement and does a lot. So I just want to be able to
start seeing the nebular appear and I can just about here so I'm gonna call
that, that. I'm gonna call this 'First Levels'. And that's that done for that layer. I'm
going to 'Duplicate' this layer by using Ctrl+Shift+D or you could always
go to 'Layer' and 'Duplicate Layer' and then we'll call this layer the 'First Adjustments'
and to this layer I'm going to do a 'Curve' stretch now so Curves allows you
to manipulate various parts of the histogram.
So here's our data and the Blacks, Shadows, Midpoint, Highlights and Whites
of the image and their corresponding brightness value we're going to do
what's called the Astro Curve and that's where you drag all this data up quite
aggressively like this. I'm just gonna put another point here just
smooth that curve out a bit and so that's the Astro curve
so we've took the data that's in the shadows of this image and we've dragged
them up to the midpoints. I'm gonna click OK and now you can see that it's got
this dodgy cast all over this, yeah? We're gonna fix that by using the Levels
adjustment so 'Colours' - 'Levels' move the 'Black Point' of the image down this is to
taste if you like this like low contrast look that's up to you, if you want really
high contrast you would move this slider down. I like somewhere in between that
will do it for me and before we move on we're gonna use the 'Histogram' now if you
haven't got a Histogram on show go to Windows - Dockable Dialogues - Histogram. With the histogram I'm gonna click it and I'm gonna select RGB and you can
see that the red value the red pixel values are lower than the green and the
blue. So to fix that we're going to use the 'Levels' adjustment. Colours - Levels. Make
sure that's on RGB and we're gonna select and edit only the red channel. So
under 'Channel' click 'Value' and select 'Red'. Now move the white point of the red
channel until it's more in line with the rest of these. Yeah I'm happy with that. I'm now going to
Duplicate this layer again and I'm gonna call this thing second adjusment layer. Before I move on with the second adjustment layer I'm actually gonna hide
these first two layers. We're now going to make a 'Star Mask'. so a Star Mask will
help protect the intensity of all the brightest points in the image - the stars - and we're going to use it throughout the rest of the adjustments
we're making. So it's a good point to make one here and to do that we're going
to go to Tools - Selection Tools Colour Select. Ssing a threshold of about 50,
so that means this the color we sampled plus 50 units each side of that colour will
get selected. I want to zoom in on a star I want to select that star, just be using
that color select tool. You can see how it's put a marquee around those stars. Now I'm gonna go to Select - Grow. I'm
gonna expand that selection by 2 just so it encompasses the entire star. If you
don't like that it's got some of the halo around it you can always change
your threshold and try again or adjust your grow factor.
I'm just going to carry on as it is because we're doing a tutorial. Ctrl+C
and Ctrl+V to copy and paste that into place, and then press this button here to
create a new layer. Because it's only a floating selection we can't edit it, so
click create a new layer. Call that 'Star Mask'. So if I deactivate that there you
can see what we've got going here. We've got all these stars, they've just been
isolated from that layer and I'm going to actually move the star mask layer
below the second adjustment layer now. And this is going to become clear very
soon, and to to demonstrate that I'm gonna hide
this layer.Now it's time to make the layer mask. So I want to make a Layer Mask using the Star Mask. Press and hold Alt and click the thumbnail of the Star Mask Layer. So that's reselected all those stars. Now go to 'Layer - Mask - Add Layer Mask'. Initialize the Layer Mask as a Selection and invert the mask. So what
this does - what this means is that we've now made a white mask with black
selected points on it. Because with the layer mask anywhere that's black you see
through to the layers below, and anything that's white you see the active layer. So
in this example I'll show the layer mask I'm gonna use ctrl shift & a to deselect
that. This is our layer mask so where all these black points are where the stars
were and they are no longer editable on this layer
they are seeing down below anywhere that's white is the second adjustment
layer you can see this in demonstration again so well those white points are we
just seen through if we reactivate the star mask layer we can now see through
the star mask layer. See? This way we can do edits on this way we can do edits on
the active layer without damaging the stars, yeah? So click the thumbnail of
second adjustments and we are ready to get back going. I'm going to do another
curves adjustment now so we're gonna go to colours and curves and we see the data
has moved up and do another curve another Astro curve but not nearly as
aggressive, and I bring it to the midpoints but not all the way
down here. Yeah. Can you see the can you see the star mask it work? So I want to
move that about there and just like before go to colours and
levels and move the black point to get your contrast back, and if you want to
brighten up again you can always move the white point of this layer. Okay now
I'm gonna crop this image if you look carefully around the edges you're gonna
see areas that aren't as bright as the main point of the image, and that is
because the image was dithered, and that means each picture had moved slightly
from the picture - the last picture - and that leaves this border around it where
there's not as much signal-to-noise. So take your there's not a much signal even.
So take your rectangular selection tool or the rectangular marquee or whichever
you want to call it. Just click inside and try not to fall off your left mouse
button. Click and draw a marquee around it, from there we want to go to 'Image - Crop To Selection' and then use 'Ctrl+Shift+A' to deselect. If you don't
use the keyboard shortcut you can always click 'Select' and click 'None'. So we've
now cropped the image we've done some curve adjustments. We've done some levels adjustments and we've got a star mask in place. I now want to select just the nebula I
want to start editing the nebulosity independently to the background and to
do that I need to select the nebula. Right so the easiest way to do that I
found in GIMP is to go to 'Tools -Selection Tools - Colour Select' again with the threshold I use of about 50 I'm going to
click inside in the nebulosity here. So I want to sample this colour for example
and what that's done is is took that value of red and 50 units that side and 50
units that side and selected everything that's within that colour range.
and this is what has left us so we're gonna refine this selection now by going
to 'Select - Feather' and feather it by 10 points and that just as you can see
cleans the selection up. Then copy and control paste that make
it a new layer so it's no longer a pasted floating layer and I'm gonna
apply if the star mask again to this. So again I'll click the thumbnail of the
Star Mask, click select your pasted layer I'm gonna call this the nebula
adjustment layer. So with the nebula adjustment layer selected go to 'Layer - Mask - Add Layer Mask' by selection and an inverted mask. Deselect so the nebula
adjustment layer is looking through to the second adjustment layer which is
looking through to the star mask click the thumbnail of the nebula adjustment
and we're gonna start working here now and then do a contrast curve so I'm
gonna show you the contrast curve this is otherwise known as the S curve and
you're gonna see why. I'm gonna take take the image in about like this part of the
image I'm going to pull it down on that part of the curve and then higher up in
the highlight section, I'm gonna increase the value. Now that's quite a high contrast curve
and that's actually really modest like if you put it all the way down there can
you see what's happening? Can you also see how the Stars are still protected? I may raise the white point again so
go to colour levels raise the white point and if you look what you had look what
you've got is increased contrast is increased colour and, if that's too much
for you can always just change the opacity of this layer so I'm gonna put
about 66% maybe I'm gonna put this to do 50% yeah. There's two ways now to edit the
background colour. I'm gonna hide the nebula adjustment layer I'm gonna go to second
adjustment layer and you can do we're gonna do the same on to the background
you can either go to selection tools colour select and try to hit a good point
in the background. But you're gonna notice that there's a lot of colours are
bleed over so you're gonna select a lot of the nebulosity and I show you
what we've got here go away toolbar, hid you for a reason! You see you still
got a lot of the nebulosity it selected you could always adjust this or you
could try to add add more contrast and then do it again. So let's see what
happens if we adjust this there so let's go let's go to colors let's
lower the black point. Yeah that's working for me. or instead of doing that pasted layer,
I'm gonna call that 'Background Adjustment'. instead of doing that you could have
just selected the second adjustment layer and did the same thing. But because
that's gonna that's gonna adjust everything including the nebula adjustment
layer - as the nebula adjustment layer's translucent we're seeing through
it slightly - it will adjust the look of that. So I'm gonna keep it with the
background adjustment layer and if you wanted to you can always apply a star
mask to that layer as well. There we go, so what did, we have, let's do
a run-through: We started with that then we got to that, we made our star masks we
have that then we adjusted the background sky intensity, and then we did
the nebulosity and that might be too much contrast for you it might be a good
contrast for you. Like I said I'm just trying to teach you the tools, so then
you know how to make the edits as the way you see fit. So I now want to
combine all these layers into one layer but I still want to leave these layers
as they are. So I'm gonna go to 'Layer' 'New From Visible'. So that's the visible
layer now. What new from visible does is: everything that we could
see is made into a new layer. I'm gonna call that
stamp because it's what I do in Photoshop, and the more familiar with it
and it's called a stamp. If you want to increase the nebula even more
you can always just drag that up. You could, for example, duplicate your Nebula
adjustment layer. Go on top there and let's see. Let's increase the colours.
Let's go to saturation and let's increase the saturation a bit so that's
too much. Remember this is only 50%
transparent I'm gonna make that probably 33% up I change the opacity to 33% so
it's just about there. What're the RGB layers like? mm-hmm mm-hmm
exactly as I thought I'd see. and once again you can do the same with
the background adjustment there for example we're gonna put that there if
you want to add more contrast you can always go to Colours - Brightness/Contrast
you can raise the contrast up if it lets me select it okay.
so playing around with the contrast I'm not gonna keep it that's why I was just
throwing around with those layers but that's where you'd then make them
adjustments, and as you can see it's made a bit of an adjustment but I'm just
gonna delete that layer now. I'm happy with this. Right, I'm gonna go to layer again
new from visible and call that stamp 2 Let's do a bit of noise reduction. I
think this is only two hours of data so you can see that it is quite a bit noisy.
So to do noise reduction we're gonna go to we are going to go to
Filters - Enhance - Noise Reduction. I'm going to do a strength of about six. let's do strength 6, let's see
what happens. Noise reduction can take a very long
time, especially on the full-size image. Just another reason why I made it
smaller so noise reduction generally softens the image quite a bit it's made
it quite starless, so you always just put these back on top just to bring some that detail back in. and then change that opacity to about
33% so I just want to start getting some of the details back in again, let's
change the mode so put the mode to the luminance. I'll show you what that does so if
you put the background adjustment back on you get all that noise back in and
you back to square one, but if you set it to luminance. it kind of is a bit best of
both worlds you've done noise reduction and you've got some of that detail and
contrast back. So I'm gonna do the same thing from the nebula adjustment layer
gonna set that to luminance and probably to 100% opacity. Nah we'll keep it at 50. So
noise reduction, bringing some of the star detail back in and that's where we
are with that. If you don't want the image to smoothen out that much you
can always use lesser noise reduction. go and stamp from visible again Stamp 3. I am going to see do I want to bring
the white point up anymore? I think I do but before I do that - you guessed it - the
star mask comes back into play. so if you need to move the star mask up to
here now because we've been stamping the it's lost the star mask unless you want to
apply the star mask to each stamped layer just move the star mask. Apply layer mask
so now I'm going to do my levels adjustment now that my stars are
protected. Let's see about adding a contrast curve
into this I'm not feeling that right think we're about nearly there. I want to
now show you how you can do some selective contrast enhancement. This is
something I like doing on most of my images so I'm going to show you how.
We're going to make a duplicated layer of this so we're gonna do another we're
gonna - you can either stamp it or duplicate it. I'm
gonna delete this layer mask because we're going to need another layer mask
and call this the contrast layer. What I'm gonna do is I will go to Colours - Curves and I'm gonna put quite an extreme contrast curve on this, maybe
even something like that. Maybe go to Colours - Brightness/Contrast. Very slight and very just a very bit. You might now be sitting wondering
"what the heck is going on?", we're going to use a layer mask so we're going to go to
Layer - Mask - Add Mask, and I want this one to be full transparency I want to make
the black mask fully transparent that was the wrong mask. So you want to make a black mask so it's
fully transparent so you can completely see the layer underneath then take a
white brush, so paintbrush - white brush and I'm gonna use it about size size 50
is working for this and we we're gonna want to paint white paint. So do you remember what I mentioned about layer masks? White shows through to the
one below it so black hides that mask and white shows through. So we're gonna
we've hidden everything using a black mask so we're we paint white we're gonna
see through that mask. So we want a nice soft brush not a lot of force just
a nice soft brush and paint white paint onto the areas where you want that
contrast to show. You can always adjust the force, adjust
the opacity of the brush as well to start blending it in. Just paint this anywhere you want a bit
more contrast, so maybe a bit there. I'm gonna paint a bit more, a more
transparent brush just to feather this out so it's transition isn't as
harsh, and now with the layer mask selected I'm gonna go to
'Filters-Blur-Gaussian Blur'. I'm gonna put a bit of a blur on to this
maybe 20, yeah. There's two ways you can now do this
either you can change the opacity of this layer. it's a blending mode normal and
change the opacity or you could go to if I can find it in this one. Multiply and
again just play with the opacity. I prefer the normal mode so that's a bit
of selective contrast added to this image and from there yeah I'm gonna go
to new from visible and I'm just gonna rotate this image now. Cuz this wasn't
the orientation I wanted so I'm just gonna go to transform rotate 180 degrees.
That's the picture I wanted and that it's very I'm very happy with that
actually for GIMP. I'm not used to GIMP so this is it now this is the finished
article after the rotation this is how I wanted it. So with any luck from this
tutorial what you've gained is knowing how to make Levels adjustments, curve
adjustments, why you would use them changing individual channels on a curve
on the levels for example playing with the red. Using layer masks, making star
masks, how to use the colour select tool to pull out the nebulosity and then
make adjustments individually to layers underneath it. I'm still looking for a
good way to do star reduction in GIMP but using the noise reduction mode and
then luminance layers over that to bring some
detail back in seems to work quite nicely. and then just adding selective
contrast and other adjustments like like saturation and such. So if this has been
helpful to you let me know if it's been helpful and drop it in the comments, feel
free to use this data if you decide to put it up on social media and share it
then please tag me in it so I can see see the results of your work with my
with the information I've given. and yeah if you enjoyed this, let me know - give it a
thumbs up if you thought a lot of waffling give it a thumbs down, and if you
need any more and want any more GIMP tutorials let me know and what you'd be
interested in. Thanks very much for watching I hope you have a good day
clear skies and keep looking up and keep them cameras clicking. See you
later.
