Pixel intensity overflow in HDR mode about tev HOT 7 CLOSED

Hi Wenzel, I can't reproduce the issue on my macbook, unfortunately -- the pixels just keep getting brighter and eventually saturate to white. The attached screen recording is representative of what I see.

You can also see flickering that I've started to experience since switching my M1 Max that I mentioned recently. Seems at first like a separate issue (no overflow behavior), but who knows -- might be related in the end.

from tev.

Before I start digging deeper into tev, could you check whether the same overflow occurs when cranking the brightness in one of the nanogui samples? Thanks!

from tev.

It's on a Pro Display XDR in my case, but with the not-quite-latest macOS version (which may be relevant here, Apple has been doing a lot of work on HDR support in the OS). I plan to give this another try with Monterey when I receive my M1 machine in February. (Busy with the SIGGRAPH deadline until then, too .. ;-))

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Heh, no hurry (and a successful crunch!).

Another thought: if the overflow indeed happens at reasonably large values (e.g. an eye-searing 64k), I'm happy to add clamping in any case -- just let me know if you find a specific value.

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The magic value seems to be 64, and this fixes it:

diff --git a/src/UberShader.cpp b/src/UberShader.cpp
index 91d9a8a..68b4d88 100644
--- a/src/UberShader.cpp
+++ b/src/UberShader.cpp
@@ -355,9 +355,8 @@ UberShader::UberShader(RenderPass* renderPass) {
                         ),
                         1.0f
                     );
-                    if (clipToLdr) {
-                        color.rgb = clamp(color.rgb, 0.0f, 1.0f);
-                    }
+                    color.rgb = clamp(color.rgb, clipToLdr ? 0.f : -64.f,
+                                                 clipToLdr ? 1.f :  64.f);
                     return color;
                 }
 
@@ -377,9 +376,8 @@ UberShader::UberShader(RenderPass* renderPass) {
                     ),
                     1.0f
                 );
-                if (clipToLdr) {
-                    color.rgb = clamp(color.rgb, 0.0f, 1.0f);
-                }
+                color.rgb = clamp(color.rgb, clipToLdr ? 0.f : -64.f,
+                                             clipToLdr ? 1.f :  64.f);
                 return color;
             })";
 #endif

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Here is that that looks like by the way.

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Thanks for checking! 64 seems rather low, to be honest, but still a factor of ~4 above what my highest dynamic range display (the laptop) can output. So... I doubt the extra clamp affects anyone as of now. :)

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