Tip: Don't forget to save often, Gimp does have a tendency to crash! xD
Let's create a new document in Gimp. I will make mine rather small, about 800x1280 pixels at 300dpi. I recommend you make yours a lot bigger if you want it to be an actual movie poster size, though. I'm not printing mine, so this size will do. Create a new layer named "Gradient BG Overlay 1." Get out the blend tool. Make your foreground color #070805 and your background color #030d19. Apply the gradient from top to bottom while holding down the CTRL/CMD tool to keep the line straight.
Let's create a new layer and name it "Aurora." Go to Filters > Render > Clouds > Solid Noise. Use these settings:
Be sure Randomized is checked and click ok. You should now have some clouds on this layer. Get out the Perspective tool and distort the clouds so that the top half is larger than the bottom half, like in mine below.
Click ok when done. Change the layer mode to Dodge and lower the opacity to 50%.
Now we are going to create a custom gradient for this. Unfortunately, I don't feel like explaining the gradient making process, so I have created it for you. Download it from here and put it in Gimp's gradients folder. Hit the little refresh button in the gradients dialog and it'll show up.
Create a new layer above your clouds layer named "cloud gradient overlay 1." Apply your gradient on this layer from top to bottom holding down CTRL/CMD. Set the layer mode to Multiply.
Now we will add the hero into the poster. I used this photo courtesty stock.xchng. Cut the man out of the background and place him into your document on a new layer named "hero." Let's make him silouhetted by going to Colors > Brightness/Contrast. Lower the brightness all the way. You may have to do this a couple of times to get him to near complete dark. Scale the man down a little bit to make him stand in the bottom left corner. (Please note the image below has been brightened so the hero is viewable.)
Now we will create terrain for our hero to stand on. Create a new layer underneath the hero layer and name it "terrain." Get out the pen tool and draw some real simple & quick terrain. Convert it to a selection and fill it with black, like in mine. Group the hero and terrain layers by clicking the little chain lock icon next to the layer.
Create another new layer underneath both of those layers and name it "Linear Gradient 1." Apply a black and white linear gradient from top to bottom. Make sure black is the foreground color. Set the layer mode to dodge and lower the opacity to 80%
Step 6Now we'll add in our planet. I am going to use this planet. Add it as a new layer, named "planet," into your document. place it in front of everything except for the hero and the terrain. Change the layer mode to Screen and keep the opacity at 100%. I also went through and softly erased the majority of the stars in the background of the image.
Add a new layer above the planet layer. Go to Filters > Render > Clouds > Solid Noise. Use these settings:
Change the layer mode to Dodge. Get out the Eraser tool and, using a large, soft brush, brush over the parts that you don't want to appear on the final image. Duplicate this layer twice. In the 3rd copy, invert it by going to Colors > Invert and then change the layer mode to Soft Light and lower the opacity to about 50%. Use the eraser tool again to adjust some areas.
Create a new layer underneath the hero and terrain layers named "swirl." Render some clouds like before. Go to Colors > Curves. Adjust it so that you have a nice variety of grays, like below:
Click ok. Get out the Elliptical Selection tool and make a nice circular selection around the swirl. Go to Select > Feather and feather it by 50 pixels. Get out the perspective tool and distort the swirl so that it faces the planet, like below. Click ok when done.Step 9
Set the swirl layer to Dodge and duplicate it. Create a new layer above the swirls and name it "Lens Flare." Fill the layer with black. Go to Filters > Light and Shadow > Lens Flare. Render a lens flare over the area where your swirl is. Set the layer mode to Dodge. Resize the layer if needed to cover your swirl.
Let's create another new layer under the hero and terrain layers and fill it with black. Get out a large, soft brush and give it this color #5a708e. Paint some areas mainly in the center and close to the light sources. Change the layer mode to Soft Light. The clouds will become a bit darker and bluer.
Create a new transparent layer under the hero and terrain layers and name it "beam." Get out a large, soft brush tool that's white in color. Make the brush 50% opaque. Draw a straight line that starts in the center of the swirl and ends touching the little planet protruding from the bigger planet. You'll need to play around with brush sizes and opacities to achieve a look like I have below.
Now we'll add our stars. We'll create big stars and small stars. Create a new layer under the planet layer and name it "small stars." Fill it with black. Go to Filters > Noise > RGB Noise. Keep Independent RGB checked and set all 3 values to 1.00. Click ok. Set the layer mode to Screen.
Go to Colors > Levels. In the top bar, set the values to 125, 1, and 211. Click ok. Go ahead and use the eraser tool to erase parts of the starfield that are too strong.Step 13
Now for our large stars. Create a new layer and name it "big stars." Set the layer mode to Dodge, and get out the brush tool. Using a soft and white brush, randomly scatter some stars. Make the opacities and sizes vary, but don't go too crazy with this part. Lower the opacity of the layer when done.
Now we is addin' the moon. I'm going to use this stock photo. Place it in your document on a new layer and name it "moon." Rotate the moon so the lighter side faces your planet. Go to Colors > Hue/Saturation. Give the moon a blue hue. Set the layer mode to Dodge. Duplicate the layer, and go to Filters > Blur > Gaussian Blur. Blur by 10 pixels. Change the layer mode to Screen and lower the opacity to about 8%.
In the end, I decided I didn't want the hero or terrain, so I got rid of them. Well, enjoy!