Alright, the bootscreen is the first screen you see that appears when you start a game. Editing this is becoming somewhat scarce knowledge (imo), and I'd like to share my knowledge.
*Note: This tutorial is only for people that know a little about image editing in the first place. If you don't know what indexing an image is, or tilemap editing, or how to edit palettes, then this isn't for you.
Okay, you need these tools to do this.
GIMP or Paint (or another graphics editing program)
Sphere (not necessarily)
Okay, step 1. The first step is to create your bootscreen.
After you've made your bootscreen, you want to index it with Irfanview. (Also, export the palette for later!)
For my example, I will use this:
Next step. Now that you have your image, you want to remove all repeated 8x8 tiles that appear in the image. To do this, I recommend using Sphere, however, you can do it by hand. Once done, don't forget to make sure your image is indexed!
Need help? Clicky.
At this point, I am here:
The next step is to take the tileset created in the last step, open it in NTME, and create a tilemap. Make sure that the size is the preset size "FR/LG TS" (32x20 tiles). For this tilemap, all the tiles need to be in the palette 0.
This is what my tilemap looks like:
Okey, open unLZ.GBA. The first part is to insert the tileset. In unLZ, go to image 207 (FR) or 209 (LG). Now, it won't look like the tileset for the bootscreen, but it is. Insert the image, and repoint the image data if need be. (But, don't import the palette!).
At this point:
Okay, now in unLZ.GBA goto to 208 or 210. This is the tilemap for the bootscreen. Import your tilemap, and repoint as necessary.
Import the tilemap:
In the ROM thus far:
Time for a palette change! (But it's working so far! )
Finally, the palette editing (if necessary). Open your ROM in APE. Next, go to 00402260 (FR) or 0040209C (LG). Once you loaded the palette, edit away! If you did, import your palette from earlier. However, it (probably) throws an error. To get the palette to load, just keep trying to load the palette until the program actually loads it but crashes. When the message comes up about the crash, quickly press "Print Screen" and save the loaded colors. Paste this image in Paint or GIMP, and manually input the values.