Renaming the shaders again, because the extensions I gave them were confusing GitHub's syntax highlighting.

shaders/imagePass.frag.glsl

@@ -0,0 +1,14 @@
+precision mediump float;
+uniform sampler2D tex;
+uniform sampler2D bloomTex;
+uniform sampler2D backgroundTex;
+varying vec2 vUV;
+
+void main() {
+	vec3 bgColor = texture2D(backgroundTex, vUV).rgb;
+
+	// Combine the texture and bloom, then blow it out to reveal more of the image
+	float brightness = pow(min(1., texture2D(tex, vUV).r * 2.) + texture2D(bloomTex, vUV).r, 1.5);
+	
+	gl_FragColor = vec4(bgColor * brightness, 1.0);
+}