<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto">Hi Arun, <div><br></div><div>This might be a something you have already looked at but is your monitor gamma corrected for nonlinearity? The same change in input for darker background results in a smaller change in brightness than for brighter background (See below), which might explain better detection at higher brightness. </div><div><br></div><div><img src="cid:3A5EDF07-F4EB-4B10-8B9A-D96FC9F30B68" width="290" alt="01_4.jpg"><br><br>Regards,</div><div>Anshul </div><div><br><div dir="ltr">Sent from my iPhone</div><div dir="ltr"><br><blockquote type="cite">On Aug 24, 2022, at 1:29 PM, SP Arun <sparun@iisc.ac.in> wrote:<br><br></blockquote></div><blockquote type="cite"><div dir="ltr">
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<span class="x_elementToProof" style="font-size:11pt;margin:0px;background-color:rgb(255, 255, 255)"><span style="margin:0px">Dear visionlist, </span></span>
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We have a brightness perception puzzle in the image linked below. </div>
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<span class="x_x_elementToProof" style="margin:0px"><a href="https://drive.google.com/file/d/1QpWT48uA9R1ZG48ERy4F3osvxPgoy4qT/view?usp=sharing" data-auth="NotApplicable" style="margin:0px">https://drive.google.com/file/d/1QpWT48uA9R1ZG48ERy4F3osvxPgoy4qT/view?usp=sharing</a></span>
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When we tried to find the smallest change in brightness detectable against a uniform background, we found something strange: for dark backgrounds, we found that only large brightness changes could be detected<span style="margin:0px">, whereas for brighter backgrounds,
we found that much smaller brightness changes could </span><span style="margin:0px">be detected. </span></div>
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This was puzzling to us because this is the opposite of Weber's law -- by Weber's law we would expect that the threshold brightness change for brighter backgrounds should be larger than for darker backgrounds. But we observe the opposite. </div>
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All this must be because of contrast detection somehow. But we are unable to think of reasons why this is happening. Any ideas? </div>
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Regards, </div>
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Arun</div>
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<div style="margin:0px">---</div>
<div style="margin:0px">SP Arun</div>
<div style="margin:0px">Professor </div>
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<div style="margin:0px">Indian Institute of Science</div>
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<div style="margin:0px">T: +91 80 22933436 </div>
<div style="margin:0px">W:<span> </span><a href="https://sites.google.com/site/visionlabiisc" data-auth="NotApplicable" title="https://sites.google.com/site/visionlabiisc" style="margin:0px">https://sites.google.com/site/visionlabiisc</a></div>
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