 Hi everyone. This tutorial will take you through the steps of creating a color image from your individual black-and-white fits images. So the fits images or the fits files are the ones that come directly from the telescope after they've gone through the processing pipeline and the color image in this case is made up of the red, the blue and the V filter images. So the red, green, red, green, blue images. So we're going to be using GIMP. GIMP version 2.10 now has support for fits files, which means we can open them in GIMP and we don't need an extra software like FitsLiberator. FitsLiberator, however, provides a lot more functionality than GIMP because it is designed for scaling fits images, but GIMP will do for now. So we're going to go ahead and open these images. So I'm just going to drag and drop them into my dock Mac. Once this pops up, we're just going to go with the default settings. So that's the red one. Maybe the little one red. Open the green one now. There. Green one. Finally, blue. I'm going in the order of red, green, blue, just just because it's easier. You can put it in the order you like. So now the first thing we've got to do is we've got to stretch the image. Right now the data in this image is essentially white as you can see the white dots and black, but we want to get the entire range, the grayscale range going from white to black. So in this case, the first thing we've got to do is I'll just show you why we do this. If you go to levels, so we clicked on, I'll just redo that, click on colors, levels, you notice that the histogram is right towards the left, right? It's smushed right towards the left. And what we need to do is bring it out. So we can control it a bit more. And so what we do is we go to exposure, click on colors, then exposure, and we can bump up the exposure to a high value. We're gonna do too much. Now we're doing all of this visually, right? We're trying to get as much detail as we can without overexposing the white regions. Now it is also dependent on your image, but the most important thing at this stage is just to get enough information out. So once you're happy with the exposure, I was happy with the exposure. I clicked okay. Do it again, color, exposure, bump it up to a high level. I'm just gonna take it up to there and go okay. That's done. The next thing we're gonna do is we're gonna click on color, levels. Now you can see that the histogram is broader and it covers the gamut of the range from white to black. What we're gonna do is we're gonna try and cut off those pixels over there that we don't need. We're making it darker there. Oops, you shouldn't have done that. Now the white, you've got to be very careful because as you make it more white, you lose the white regions. They get overexposed, so you don't want to do that. You want to get as much detail as you can and you want to make the sky as black as possible without losing too much detail. Again, you can't emphasize this enough. This is all visual, right? Click on okay. We apply the same thing to our green image or V filter image. Take the exposure. We bump up the exposure as much as we can, trying not to lose detail over-exposure too much. Click on okay, levels, colors, levels. Now we get the histogram. We cut off the black as much as we can give the sky black. A little bit of detail there. Now as you play with this yourself, you'll get a feel for your own images because every nebula is different. The amount of exposure for every image is different. So while you are playing with different types of objects, you will get a feel for how much to bump up the exposure enough. Okay, that is our blue image. Levels. Okay, so we have now our red, green and blue images. Now we need to combine them into one file. So let's go to our red image. That's our red image. Let's rename this layer to be red. So we are aware of it. Let's take a blue image. So now we'll be green image. Sorry, V, which is our green image. Select all, edit, copy. We go to our red file and go edit, paste. Let's paste it there. We're going to call this visible. Actually, I'll call it green. Hit enter once you type in the name. There we have a green, we have a red, green, and now we go to our blue. Edit. Also, select all, edit, copy and go to our red file over here and we edit, paste. Double-click on that and type in blue and hit enter. Okay, so you have, now you have your three filters or your three images taken in three different filters stacked up on top of each other. Now we're going to color them. So we're going to color them relevant to the name of the image. So here we have the red image. What I tend to do is turn everything off and just turn them on one by one. You can just click the I icon here. Excuse me, turn it on and off. So red, colors. Oh, forgot one step. Most important thing, image mode. See how it's on gray scale? We need to convert that to RGB so that we can actually apply colors. There we go. It's done. So remember image mode RGB. Now we can go click on colors, colorize. So this is the red image. We can click on this colored bar and we're going to put the red up to a hundred, green to zero, blue to zero. Click on okay. Now, actually let's make the hue as one and let's make the lightness negative 0.5. So actually, so I'm going to make it red, hue one, saturation one, and that lightness is negative 0.5. That's for the red one. Now you turn on green, we click on green. We don't need to go to image RGB because the whole image is now made into RGB. Excuse me. And then we click on color, colorize. That's a green image. We click on the color bar. We put green to a hundred, blue to zero, red to zero. Click okay. We leave that as 0.3333 and we make this one negative 0.5. So lightness is negative 0.5. That's our green. Then we turn on the blue, click on blue, colors, colorize, click it here and make that blue one hundred, green zero, red zero. Okay, we leave that as 0.6667, saturation is one and over here we make the lightness negative 0.5. Okay. So now you have your red, green, and blue. What we've got to do is now we've got to allow the light or the color from every layer that's underneath each other to come through. And what we do is we change the transparency mode. Over here in your layers palette, you can see mode. So select blue, click on that, click on mode and select screen. Then green, click on mode and select screen. There we go. You can see that it's a bit green. It's not quite similar to the image I showed you at the start. Here's where we have to manually now adjust the colors for each one to be able to get the color palette we think this image should be. So one rule of thumb when you're doing astronomical images is you want to try to get the sky as black as possible. Right, and there's different ways to do this. Now one way is to change the mixing of each of these colors with levels. Okay, I'm just going to show you that way first. So I've clicked on blue, gone to color and levels. As you can see, I can change my histogram and you can see that this is changing so I can make it a bit bluer. Right, I can make it greener. Now I know for a fact that this is the image which should have a red here and a blue. That's why I'm playing it in such a way that I can get those colors back. Again, whoops, this is completely visual. Okay, I can go to the red colors, levels, and I can do the same thing in the red one. That loses the sky. So once my sky, whoops, was too much. Once my sky is as black as it can be, now depending on how your monitor is calibrated, you will get different tints on your screen, but play with it. You will get a hand of it for your monitor. What you can do now is once you get it to a stage that it's roughly okay, you can go and click on this icon over here, layers menu, I'm going to do it again from here. You can do it either from that icon or you can do it from up here, layer, new from visible. So now it creates a merged layer called visible, combining all of those three. So I'm going to put that up there. There we go. Just drag it on top. I'll turn these off because I don't need them. So our visible layer, now we can actually go into colors and we can play a lot more with this. For example, if we want to bring out a bit more of the reds, we can bump up the saturation a little bit. Oops. Bump the saturation up a bit more. We can still go into levels and we can make the sky darker. We can bring a bit of the vibrancy back, right? We can go to color balance and we can do these manually so we can add more red to the image. Can you see how it's changing? You can split the view so you can actually see how it's changing. We can do that on mid-tones. If you don't like it, just click reset or you can go to shadows. As you can see, it changes that. I can get a bit more blue in there, right? But remember, if you change it, it's going to change it all over the image. So you've got to be very careful when you're doing that or you can change your highlights. And within your highlights, you can make it a bit more green-tinged. There you can see the middle one changes. We don't want that. So you can play with these as much as you want to get roughly the color that is suitable for that image. Now people can take artistic freedom and make it all sorts of colors, but this is what's called the Hubble palette. If your eyes were sensitive to light in these wavelengths, very sensitive to light in these wavelengths and could detect this slight nuances in the colors, you would be able to see this object. That's the foundational thinking behind it. So basically, at this stage, you should have an image like that and then you can go and save your file in whatever format you want. You can save it as a TIFF file or a JPEG file using GIMP. But this is basically where it is. As I said, there's a lot more control. If you think you can make more changes, you can go into these individual layers and make those changes. So that's the basics of it. Feel free to play around and see how it works for you. Thank you.