Hi all My problem is a little complicated. The general idea is to perform multipass rendering, first pass suppose to fill float texture : glTexImage2D ( GL_TEXTURE_RECTANGLE_NV, 0, GL_RGBA16F_ARB, w, h, 0, GL_RGBA, GL_FLOAT, 0); with clamping float values disabled : glClampColorARB(GL_CLAMP_FRAGMENT_COLOR_ARB, GL_FALSE); and additive blending enabled : glBlendFunc ( GL_ONE, GL_ONE ); Than second pass suppose to use result of first pass, thats why befor second pass starts I perform copying color values from frame buffer to my float texture: glCopyTexSubImage2D(GL_TEXTURE_RECTANGLE_NV, 0, 0, 0, 0, 0, w, h); float fbuf = new float [ w * h * 4 ]; glGetTexImage(GL_TEXTURE_RECTANGLE_NV, 0, GL_RGBA, GL_FLOAT, fbuf ); The problem is values are clamped to 0..1. Anyone knows what could be the reason ?? I tried the same using EXT_framebuffer_object and it works correctly but it is much slower on my geforce 7300GT. Thanks in advance. Marcin