Try this:
CCRenderTexture *renderer = [CCRenderTexture renderTextureWithWidth:tx height:ty pixelFormat:kCCTexture2DPixelFormat_RGBA8888 depthStencilFormat:GL_DEPTH24_STENCIL8];
[renderer beginWithClear:0 g:0 b:0 a:0 depth:1.0f];
[sprite visit];
[renderer end];
UIImage *img = [renderer getUIImage];