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Etching: reducing size of vector graphics


#1

Hi,

I am simply trying to scan images that I draw by hand, reduce their
size to around 30% of the original, invert the image or make a
negative of the image and finally print the image onto pnp blue so
that I can etch it onto my silver jewelry however when I reduce the
image size I seem to lose the image quality. I have been using
photoshop and illustrator. Has anyone tried something similar to
this?

I draw patterns that I would like to etch into my silver jewelry.
The original hand drawn image’s size is too large to be etched onto
say, a ring. An example would be trying to print a 12" wide smiley
face on a 4x5 card. The image needs to be shrunk so that it fits the
card.

Here is my current process: I scan the drawn 8x11 image. The image is
simply a pattern drawn in black ink on white background. I use
Illustrator to turn the scanned pixel-based image into a vector
graphic. Since this is a line-based drawing, I understand that using
vector graphics is the way to go. After saving the file in
Illustrator, I open it in Photoshop. In Photoshop, I invert the
image because this is how I want the image to etch (turn the black
lines into white and the white background into black). Now, I save
this new image in Photoshop. Last thing I need to do before I print
the image is to reduce the image to about 30% of the original. Here
is where I get into trouble: the lines of the vector graphic lose
their quality and detail once resized. They become blurred. Does
anyone know how to reduce the size of a vector graphic without losing
the details of the image?

Thanks,
Chris


#2

Hi Chris.

Step one: if you’re using Illustrator, forget about Photoshop. You
don’t need it.

Step two: you say you’re using Illustrator to “turn the scanned
image into a vector graphic”.

how are you doing this? Are you manually re-tracing the graphic
using the pen tool, or are you using the auto-trace function? The
reason it matters: Auto-trace is psychotic. Yes, it’ll get you a
(monstrously huge) vector that loosely resembles your original
bitmap, with very little work on your part, but the odds are that the
control points will be belligerent, numerous, and nowhere near where
you really want them. Auto-Trace loves fills, rather than stroked
lines, which works OK for ‘illustrations’, but for etched graphics,
stroked lines tend to give crisper results, especially when you know
you’re going to be reducing the size. (It also lets you fiddle with
line weight on the reduced image independent of overall image scale.
Most handy, especially for etchings.)

(Knowing that you’re going to be tracing a scan, I’d get in the
habit of drawing the graphics much larger than you really need them.
That way any little wobbly bits get evened out by the reduction.)

So step three is: trace the image by hand, using the pen tool. Yes,
it’s a pain, but your other option is to engrave it by hand. Pick
your poison.

To invert it, just make a big black square, (fill it with black),
send that to the back, and lock it.

Then select all, and set the strokes to white.

Unlock the background block, make sure the graphic is centered
within it, and group them.

Then you can use the scale tool to reset the graphic to whatever
size you need. I tend to use the transform pallet, because I can do
it by inches directly from there. (ungroup the vector from the
background before you do that, otherwise you’ll be setting the size
of the background block too. You don’t care about the size of the BG
block, so long as it’s bigger than the graphic.)

Done this way, you can set the size of the graphic to whatever size
you like, with no loss of quality at all.

Regards,
Brian Meek.


#3

Are you resizing the image in photoshop or changing the size in the
print function? I do my image scaling in my photo editor not the
printer.

John
Rasmussen Gems & Jewelry LLC


#4

Try switching to a vector graphic program.

RC


#5

Photoshop is primarily a pixel editor and it sounds like what is
happening is that your art is being rasterized (turned into pixels
instead of vectors, hence its jagged, or fuzzy.) You can completely
skip the Photoshop step. Color your art the way you want it and
scale it in Illustrator. Make sure the line thickness of fine details
is sturdy enough to hold up to the amount of scaling you need. Draw a
marquee around all the elements, group them and duplicate them to
get as many as you can on a sheet to save materials. Vectors remain
sharp at any scale and are only subject to the resolution of your
printer


#6

Hello Chris,

I am wondering how you are going about creating your vectors in
Illustrator. Are you using live trace? If you are truly creating a
vector you should be able to rescale your image without losing
quality.

Non vector images i.e. Raster images may get blurred once resized as
they are made up of pixels. Vector images are mathematical equations
(shapes) made up of points and paths.

If what you have are really vectors you should be able to change the
colors within the path (e.g. black to white) and reduce them in
Illustrator without having to bring the image into Photoshop.

If I knew a bit more about your process I can be more helpful. Feel
free to message me on or off-line.

Jeneba


#7
So step three is: trace the image by hand, using the pen tool.
Yes, it's a pain, but your other option is to engrave it by hand.
Pick your poison. 

Not necessarily. After using live trace in illustrator, import the
results into your CAD software. Most should have convert function
from splines ( which is another name for vector graphics). It may
also show as a skin object or a lathe object. Does not matter. The
convert function can either directly reduce complexity or there
should be another function. The point is to reduce complexity to 0.
It should get rid of extraneous control points. If results will be
too primitive, you can bump up complexity slowly until results are
satisfactory.

If your CAD package does not have this functionality, you can convert
to polygons and switch to point cloud mode. Another name is vertex
mode, or whatever name your software uses. The control points will
show as vertexes and can be deleted manually. A bit slow but better
than tracing by hand. If results are rough, use subdivision surfaces
function to smooth it out. Render the result and than you can get it
in photoshop for further processing.

Leonid Surpin
www.studioarete.com


#8

Chris–

It would be helpful to be able to see a before and after version of
your image.

I agree with Alberic that you probably don’t want to use both
Illustrator and Photoshop. I also agree that auto-trace is more
likely o give you trouble than to help you.

If, however, your ink drawing is fairly crisp, I would try Photoshop
alone before I tried Illustrator. Especially if your designs are
complicated. The directions that follow assume that you are using
Photoshop and not Photoshop Elements (though the process would be
very similar).

Step one: Make sure you have a fairly high resolution scan. I would
try 300 ppi. The scan should be color or grayscale, not just black/
white.

Step two: Open the scan in Photoshop. Do whatever you do to look at
the scan at 100%. I’m a Mac user so I type Command-Option-Zero (or
double-click the magnifying glass icon in the control panel).

Step three: In the menu bar, choose Image>Image Size… Change the
pixel dimensions to percent and change the percentage to 30 (or
whatever percentage suits you).

Step four: Before you click OK, make sure “Resample Image” is
checked, and select “Bicubic Sharper (best for reduction).” Any of
the bicubic options are probably good enough. Your options may be
slightly different depending on what version of Photoshop you are
using. Then click, “OK.”

Step five: Before you evaluate the quality of your reduced image,
make sure that you are viewing the image at 100%. The image should be
acceptable. If it isn’t acceptable, I would like to know what is
wrong with the image, are the edges of lines jaggy, or too gray?

Step six: If you are using a Mac, type Command-I to invert the
image. You can also go to the menu bar and choose
Image>Adjustments>Invert.

–Whit


#9

There are a number of problems with your workflow.

A scanned image is always raster, that is just the nature of
scanning. So, unless you are converting the scanned image to curves
in Illustrator there is no point in going through that program at
all.

Since the scan is raster it’d be better to open it in Photoshop,
invert the colors, then bring it into Illustrator for conversion to
vector. However, since your are reducing the image quite a bit you
don’t need to convert to vector at all.

Etching can be thought of as a raster rather than a vector process,
so there is no great utility in converting a drawn image. Photographs
are always raster, and photo-etching starts with making a photo
negative, after all.

Do you produce your own film, or send the art out for photography?
Are you producing your own positives to give to an etching service,
or are you sending them the digital file?

Anyway, here’s my suggested workflow:

First, decide on the final size of the etched area. Then find out
what the optimal DPI (dots per inch) is for the imagesetter, or
printer, you’ll be using. Now you can calculate the absolute image
size you’ll be using. F’rinstance, let’s say the final etched area is
a 1"x1" square, and the imagesetter can output at 1200 dpi. That
means that the raster image which you’ll burn will have a size of
1200x1200 pixels. Each pixel will be translated by the imagesetter
into one dot in the 1200dpi matrix. Now you know how big your image
has to be in Photoshop.

Now you will set your scanner to scan at a DPI that is appropriate
for the size of your original. If you scan at 300 DPI then your
original needs to be 4"x4" to come to 1"x1" at 1200 DPI. If you scan
at 100 DPI then your original would need to by 12"x12" to come to 1x1
@ 1200dpi. Since you say you’re reducing about 1/3, then you’d set
your scanner to scan at 400 DPI to get to a 1200 DPI at print size.

Now, draw your pattern at the appropriate size, 3"x3" in our example
(3"x3" @ 400 DPI becomes 1"x1" when output at 1200 DPI). Scan the
drawing at 400 DPI and bring it into Photoshop. Clean up the image,
if necessary, and invert the image.

Here’s the critical difference in workflow, DO NOT scale or resize
the image. Image editors like Photoshop allow you to change the DPI
setting of an image without otherwise altering the image. Do a SAVE
AS… and only change the DPI (Print Size) setting of the image. This
way, no pixels will be changed, but the image will output at the new
resolution. So an image which was 3"x3" and scanned at 400 DPI, will
print at 1"x1" when output at 1200 DPI. And none of the pixels will
be changed.

This only speaks to your digital workflow. If the problem is in your
photoresist or elswhere in the actual etching process, that’s a
different issue entirely.

Elliot


#10

Hi Chris,

I have used Photoshop to enlarge and reduce logos, text, and other
designs in preparation for transfer for engraving. I have not used
Illustrator, having found that Photoshop alone was sufficient for my
purposes. I struggled a bit with this at the beginning, and would
find my images not retaining the clarity I needed. I was scanning
designs and then opening them in Photoshop for manipulation. The key
to making a clear image for transfer is to increase the resolution
of the scan, up to 1200dpi at least. Then, when opening in
Photoshop, set your preferences so that the image opens with the
same resolution as the scan, so the images are the same size. This
retains the most amount of from the original, so that
when you reduce the image it remains clear, just smaller. You can
also increase the resolution of an image once it’s in Photoshop, and
then do the reduction, but any manipulation of the image in
Photoshop does change it a bit.

Occasionally, you may have to do some clean up work on the original
design in order to remove blurry or indistinct lines within the
pattern. I would zoom in in the design, and use the eraser and
line/paint tools to sharpen whatever was looking weak, and zoom out
to check my work before I did any reducing. (Always do the
modifications on a copy of the original scan so you can return to
the original if things get too far out of whack!)

Melissa Veres, engraver


#11

Chris,

Vector graphics are the best for scaling but you just have your
process misaligned. First of all, if you are going to go to the
trouble to trace your drawing in AI then you should scale it to the
size you want in AI. This is the only way you can take advantage of
the scaling properties of vector art. Once you bring it into
Photoshop it is rerastorized. Scale it in AI then import into PS
then reverse the image.

All this said, since your drawings are so large to begin with you
have plenty of resolution to play with making the AI step largely
unnecessary. Just bring the original image into PS then open the
Image>Image Size menu. Make sure that the box “Resample Image:” is
unchecked then change the scaling dimensions as you wish. Now
reapply the “Resample Image” check and reduce the Resolution to 300
pixels/inch. Now you can apply your reverse and print. Make sure you
"save as" the adjusted file to another name so you preserve your
original. This should work quite well w/o the AI step.

Charlie


#12

I am guessing because I do not know Illustrator. I suspect something
is going wrong somewhere in the conversion of either the scanned
image into VG format or else the VG image into PS. Have you tried
this without the step of making it into vector graphics, that is,
import the scan directly into photoshop and then scaling it? It’s
hard for me to see much real advantage to the vector format unless
you are thinking of thousands (and thousands) of such images, but
since you want to etch it seems like the numbers of scanned images
would not be that large. Just a thought. HTH.

Steve