Improvement to halftoneImage()

[imrinahru]

Context/Problem:

Current halftoneImage() syntax is : `halftoneImage(img, 'type', freqency, angle, intensity);

1. The frequency can be selected from >=1 and it represents lpi (line per inch). It is counterintuitive that if a user puts larger figure in frequency, the dot size is increased with less dot in the screen, since a user is likely to be planning in terms of lpi.

At freq = 10:

At freq =5:

2. The usable parameter range for a decent print quality is quite narrow, especially for circle and ellipse. But maybe that's due to the size of the image (the solution is for the user end to use a larger good quality image)
   'circle', freq = 4, too little dots:

'circle', freq = 6, dots already became a smudge. Adjusting the intensity will alleviate the smudge only with the cost of loosing dots on brighter areas.

3. For this image, frequency set at 4 and 6 looked ok but at 3 there is appearance of moire by the color itself, which will be harder for a user to use especially when they want to overlay other colors

I know this is a lot to put into a single issue, I 'd just love to place here to start a discussion, and if it can be assigned/picked up, I'll separate the issues.
Any suggestion is appreciated!