Clearing things up

[Brian Robison]

Hi Creekers,
I wanted to start a thread to help clear up some things that are over my head right now.
I do a little photo work and I'm using Rodney's recommendations. It's working pretty good for now.
I have an Epilog so I'm trying to figure out these options.
(1) Dithering?
(2) Photo or Clip Art?

[James Stokes]

With my Epilog, with photos even run through Photograve I still use the photo setting.

[Joe Pelonio]

I'll take a stab at it. I always use the clipart setting for art that I have created in Corel, and for many photos that are sent to me as tif files. With a scanned photo or jpeg sent to me I use photo. Even then sometimes one setting or the other will work better for that photo, so some experimentation is needed. Generally the more detailed photos will be better done in photo mode. The photo mode does some dithering, which is reducing the number of colors or greys by combining them, to meet the resolution you have selected. It results in some loss of sharpness but if that number of colors/greys were reduced without dithering it would look far worse, all pixelated.

[Mark Koenig]

"pixelated"...

I like that verbiage... :p

Mark...

[Joe Pelonio]

"pixelated"...

I like that verbiage... :p

Mark...

I use it a lot when talking about low resolution artwork that people want printed big. I just checked to see if I might take credit for coining it, but no, it seems to be a word.

"Describes an image in which individual pixels are apparent to the naked eye.

The term should not be confused with pixilated, which means whimsical and bemused."

[Dave Jones]

I have an Epilog Mini-24. The two settings in the advanced tab, for Clip Art vs Photographs are:

- Clip Art - This converts shades of grays in the image into a sort of "halftone" dot pattern. Those are grid based patterns where a specific pattern or cluster of dots is used for each shade of gray in the image. A large area of a single shade of gray will have that pattern repeating over and over. The patterns used by the driver do not seem to be the classic halftone dots (where a dot at the center of a grid point gets larger or smaller with the shade of gray). The driver makes grid based patterns, but with a bit more distribution of the dots within the space of the grid point.

- Photograph - This setting converts the shades of gray of the image into a "dither pattern". There are a couple of dither methods in use by different software, and I'm not sure which one the Epilog driver uses. The most common are "noise dither" and "diffusion dither" (aka "error diffusion" or "Floyd-Steinberg" ). Dithering creates dot patterns that do not follow a grid. They are more random looking, and in most photographs are more natural looking while allowing more detail to show through than halftone patterns.

In general, the grid based patterns look best for things with large areas of single shades, and sudden changes from shade to shade (like clipart). In general the dither based patterns look best on images where the shades of gray are changing gradually, or have a wide range of different shades (like photographs). There may be times where choosing the other method works well, but in most cases the names Epilog assigned to the two settings are appropriate.

In the tests that I have done, when the original is pure black and white, with no shades of gray (no anti-aliasing, which causes shades of gray, and no CMYK black, etc...) then for me it makes absolutely no difference if you use Clipart or Photograph setting, since both deal with pure white and pure black the same. They only differ in how they deal with shades of gray. I have run Photograv images through both settings and have not seen a single pixel come out different.

Photograv, by the way converts images into dither patterns. Since it's output contains no shades of gray, it should not matter which setting you use, unless you add something else, not run through Photograv, to the engraving that does involve shades of gray.