User talk:Fhoech

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16:04, 4 April 2017 (UTC)

Talk:Luma (video)

Hi

On the Talk:Luma (video) I've asked questions about your editions. PawełS (talk) 19:03, 29 November 2017 (UTC)[reply]

Best Gamma value for Gamma correction test image

Hello Fhoech, you wrote a nice comment on the Gamma correction talk page about the Srgbnonlinearity.png Gamma correction test image. I provided a new test image with a 0%/100% versus 75.8% brightness, or ln(0.758)/ln(0.5)=0.4 or 1/0.4=2.5 Gamma value. Srgbnonlinearity.png uses 74% brightness or Gamma=0.43 or Gamma=2.3. Why the Gamma value 2.3? Please look at https://en.wikipedia.org/wiki/Talk:Gamma_correction#Gamma_used_in_Gamma_correction_test_image AndreAdrian (talk) 21:55, 26 November 2018 (UTC)[reply]

The goal is to have the same luminance for the gray patch than the surrounding black/white bars. It is assumed that alternating black and white bars equally distributed over the image area produce 50% luminance. To get the RGB value that would match this luminance for sRGB, you need to apply the sRGB transfer function (forward transform) to the desired luminance (Y), i.e. in this case input Y = 0.5, output RGB = 1.055 * pow(Y, 1.0 / 2.4) - 0.055 Fhoech (talk) 14:43, 29 November 2018 (UTC)[reply]