Create a sketch effect for photos using Brad Larson GPUImage in Obj C

Question

Hey. I would like to try the sketch effect on photos using Brad Larson GPUImage sdk in iOS . I am trying to create a sketch effect like this

But the sketch effect that I get looks like this

I use GPUImageSketchFilter to create this effect. Below are the options that I provide to achieve this effect:

 setTexelHeight:(1.12 / 480.0) setTexelWidth:(0.5 / 320.0) 

Please suggest me how to achieve this effect.

Brad going on your suggestions, I have this ...

My goal: I need to make the correct image look like the left one. Pls suggest me .. !!

Answer 1

There is information about the problem you are facing. Hope this helps you. http://iphonedevsdk.com/forum/iphone-sdk-development/103548-pencil-sketch-of-an-image-in-iphone-sdk.html

Answer 2

I saw the best sketch effect code, but I am not good at filtering, I cannot write a custom filter for GPUImage to apply this:

 float res = iResolution.x; float n0 = 97.0 / res; float n1 = 15.0 / res; float n2 = 97.0 / res; float n3 = 9.7 / res; float total = n2 + ( 4.0 * n0 ) + ( 4.0 * n1 ); const vec3 div3 = vec3(1.0 / 3.0); void main(void) { float offset, temp1, temp2; vec4 m, p0, p1, p2, p3, p4, p5, p6, p7, p8; offset = n3; p0=texture2D(iCamera,iScreen); p1=texture2D(iCamera,iScreen+vec2(-offset,-offset)); p2=texture2D(iCamera,iScreen+vec2( offset,-offset)); p3=texture2D(iCamera,iScreen+vec2( offset, offset)); p4=texture2D(iCamera,iScreen+vec2(-offset, offset)); offset=n3*2.0; p5=texture2D(iCamera,iScreen+vec2(-offset,-offset)); p6=texture2D(iCamera,iScreen+vec2( offset,-offset)); p7=texture2D(iCamera,iScreen+vec2( offset, offset)); p8=texture2D(iCamera,iScreen+vec2(-offset, offset)); m = (p0 * n2 + (p1 + p2 + p3 + p4) * n0 + (p5 + p6 + p7 + p8) * n1) / total; //convert to b/w temp1 = dot(p0.rgb, div3); temp2 = dot(m.rgb, div3); //color dodge blend mode if (temp2 <= 0.0005) { gl_FragColor = vec4( 1.0, 1.0, 1.0, p0.a); } else { gl_FragColor = vec4( vec3(min(temp1 / temp2, 1.0)), p0.a); } }