The Curves adjustment layer is one of Photoshop’s most powerful tools for shaping tone and contrast, and when combined with layer masks it becomes the digital equivalent of darkroom dodging and burning on steroids. Charlie Cramer, a fine-art landscape photographer and one of Ansel Adams’s former students, is perhaps the best-known modern practitioner of this… [Read More]
A pixel is not a little square, revisited
Just to be clear, the word pixel has several meanings. In this post, I’m referring to the value in the file, not the structure on the sensor. Alvy Ray Smith wrote a wonderful white paper when he was working for Microsoft. The title was “A pixel is not a little square.” I have referred people… [Read More]
Noise, Dynamic Range, and Print Size
Photographers talk a lot about noise and dynamic range, and camera makers are quick to publish specifications that promise ever-increasing performance. Those numbers are often reported at the sensor level: how many electrons a pixel can hold before clipping, or how many electrons of read noise lurk at the dark end. Those are useful engineering… [Read More]
Averaging captures, precision effects
When we average repeated captures of the same scene we hope for a steady improvement in signal to noise ratio. Each independent frame carries its own sample of random noise, and when we average those frames the signal adds coherently while the noise tends to cancel out. The result is a cleaner image that should… [Read More]
Aliasing with sinusoidal chirps
Today I will show you some plots similar to yesterday’s graphs, but with a different input waveform. For today’s post, I used what signal engineers call a chirp, which is a sinusoid of variable frequency. In this case, it starts on the left below the Nyquist frequency and ends on the right well above that…. [Read More]
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