Achromatic contrast, Spatial frequency and Reversing phase?

How do I change achromatic contrast in percentage of a sinusoidal grating?

How do I change spatial frequency in cycles/degree?

How do I change grating orientation pseudo-randomly?

How do I reverse grating phase?

Original text: "These two experiments were based on a common dataset, which independently varied spatial frequency and contrast. Subjects were presented with gratings of differing achromatic contrast (1.43%, 5.25%, 15.95%, 50.14%, and 99. 62%) and spatial frequency (0.1, 0.27, 0.73, 2.08, and 5.79 cycles/degree) across different blocks, in a 5 × 5 design. Every 4 s, grating orientation changed pseudo-randomly. In addition, grating phase reversed every 1 s, and grating phase was systematically varied. Each run included 15 blocks of 16 s each, beginning and ending with an additional block (12 s) of uniform gray, of equivalent mean luminance. Each subject participated in 2 scan sessions, with 12 runs (1056 functional volumes) per session. Experiment 3 analyzed variations in contrast, combining spatial frequency. Experiment 4 did the reverse."

Answer 1

[Raunak Gupta]

Hi,

In my understanding this looks like modeling of a sensor which capture the image with different inherent properties. For that you may define the system using equations in MATLAB. If you are working with color images, then you can change the contrast using chromadapt.

[João Sá]

Thank your for your help, but yeah... It was some time ago