Strokes exported from Illustrator are not showing properly

Barbara,

By the way, you say "When I export the stroks as PNG or JPG,"

Among those I would suggest your using PNG for a few reasons, one being its losslessness.

Barbara,

"Please Note that the stroke thickness is between 0.01 pt - 0.1 pt - 0.2 pt. and I can't go thicker as the design requires this thickniss."

I believe it is worth seeing this design requirement in a way that is different to the seemingly obvious, based on this:

Pic 1 - This is what does the design look like in illustrator,
Pic 2 - This is what does it look like after exporting.

It seems clear that you are satisfied with the vector artwork in Pic 1, whereas the raster representation in Pic 2 is wrong.

I believe the requirement could be that "the stroke thickness is between 0.01 pt - 0.1 pt - 0.2 pt" to get the right appearance of the vector artwork, AND the raster artwork must be made to have the same appearance.

It seems clear from you screenshots that the raster artwork is fainter than the vector artwork, increasingly so with thinner stroke weights, so you can keep the original vector artwork and work on a copy by increasing the stroke weights to get the raster artwork as close to the original as possible, which you can see by direct comparison as in your screenshots; obvioulsy, the copy will appear coarser as vector artwork.

Maybe you can increase all the stroke weights by the same amount. which might be something like 0.01 pt or 0.02 pt.

One of our scripting friends may have a script that does just that. Anyone?

Or, especially if you have a limited number of different stroke weights, you can use the Select>Same>Stroke Weight for each of them and increase it the desired amount.

Or you can select all the stroked paths and outline the stroke to get filled paths, then add a stroke with the desired amount of increase; this will also make the paths a wee bit longer, but only by the added stroke weight.

Undo would undoubtedly be your friend, or you could go back to the original and start over.

Where are these JPEG and/or PNG images going to be displayed? On a web page maybe?

If you are designing graphics that will ultimately be rasterized into pixel form you have to do two things. 1: decide what specific size the pixel-based image will be in terms of absolute pixel numbers. For instance a HDTV display has 1920 X 1080 pixels. 2: tailor the artwork's size or aspect ratio and its details to fit the parameters of those pixel dimensions.
 

Really, the dots per inch stuff means nothing unless you're actually printing something. I'm typing this on a notebook with a 120Hz 17" 3840x2160 pixel display. I don't care what the DPI of my screen may turn out to be (which is a lot) because it's irrelevant in terms of the layout where the pixel based image is going. All I care about is the pixel numbers of the "foot print" where that image is going to be placed.

In order for a 0.01 point stroke to be clearly visible in a pixel based image that image will probably require a heck of a lot of pixels.

I deal with this same sort of thing helping people understand how to create graphics for LED-based "jumbotron" signs. They think the LED display is equivalent to a TV screen, but it isn't. Most of these units have a pretty low pixel count compared to even an old standard definition TV. But they try to treat it like a TV screen anyway. If their display has a pixel count of 60 X 200 pixels it's not going to have enough pixels to resolve something like a group photograph of several people. There is no way to squeeze in extra detail between the pixels that are physically available on the display.

One thing I would suggest doing is use Photoshop in conjuction with Illustrator to create your JPEG or PNG images. Create a document in Photoshop with the pixel size your target image needs to be. Then copy/paste your Illustrator artwork into it. If certain details are being lost, not resolving, etc then the artwork has to be adjusted. I'll create a lot of graphics intended for jumbotron displays within Illustrator or even After Effects. But I create the graphics with the pixel dimensions of the target display in mind.

What's the end purpose of exporting anything at 0.01pt? Who's going to see it? Whose going to see 0.2pt?

What are you trying to create?

0.01 pt strokes don't make a lot of sense to me when you export pixels (at least not with resolution smaller than 1200 ppi)

That said: Please show us screenshots and/or the exported files and an AI demo file.

That sounds like the old problem of "over-designing" your artwork at a larger scale and then scaling it down, with the interpolation eating up your super thin strokes. The only solution to this is to really design at the actual pixel output size and use 72 DPI document resolution or you'll always run into these issues. Also check things like overprint and all that. This affects this stuff as well.

Mylenium

At what resolution are you exporting? Exporting to an image means exporting to pixels.

In Illustrator 1 pt equals 1 px at 72 ppi. Fractional pixels do not exist so there may not be enough pixels availlable.