For those of you new to computer graphics – a tracing program is necessary to convert a bitmap scan of a line art image into a vector based object that can be manipulated in a drawing program.
Typcially, the results of a trace are less than satisfactory and the computer artist blames either the scanner or the trace program when it is actually more often than not a problem of incorrect trace settings and low resolution settings of the scanner.
This article will show how to first improve the quality of the scan and then how to make the trace more accurate using Corel Trace.
This is actually where most people go wrong. A standard flat-bed scanner generally has an optical resolution of 300 dpi and an interpolated resolution of 1200 dpi or higher. The factory settings of a scanner for line art is generally 300 dpi. While this sounded high a few years ago, this is way too low for a good scan that is to be traced.
When a 300 dpi image is put into a tracing program it has a real hard time drawing straight lines and sharp corners when the image is so rough. This same image scanned at 600 dpi is 4 times sharper and now provides a much sharper image to trace around. At 1200 dpi it is 16 times sharper and a near exact duplicate of the original. The round corners you got with a 300 dpi trace now have sharp edges and the lines are very straight.
OK, at 1200 dpi the file size can be 10 or 20 mb. Yes, this is a large file and may be too large for the tracing program if there is lots of detail. You will never know until you try it. And yes, it may take the program ten minutes or more to complete the trace. I never said it would be fast – just better.
The confusing part is that most scanner manuals recommend to trace at the same resolution as your output device. This only makes sense if you are going to print out the raw scan without tracing it. If your laser printer is only 300 dpi then why scan higher? The reason is simple. The higher resolution has everything to do with how tight the trace is and nothing to do with the laser resolution!
Quality of Original Art
No matter how hard you try, if the original art is small and unsharp, there is not much you can do to make it better. Especially if you have to enlarge it 1000% to fit on a shirt. Start off with the cleanest and best art you can get. Press the customer to find a larger copy than a business card.
If you plan to fill an object with a color then the shape must be closed. If you have openings in areas the trace will leave them open and it will be harder later to close these lines. Examine the art before you scan it and take a black fine point pen and close the shapes.
Corel Trace comes with default settings from the factory that give you an adequate trace that is fairly fast. These settings are not good enough for a tight trace. When trying to trace a high resolution scan it is important to use the following settings to maximize the qualtiy of the trace.
Corel Trace Revised Settings
Over the years Corel has used different names for trace settings. In earlier versions of Corel you would change the Curve Precision, Line Precision and Curve Length to Very good. Corel then used the terms Tight and Accurate for the trace settings. In version 9.0 of Corel Trace they have a simple slider on the main page that is titled Accuracy. 100% is obviously the best.
If you follow the above suggestions of increasing the scan resolution and changing the Corel Trace settings you will have an object that will be almost identical to the original artwork. The only problem is that Corel Trace will only handle certain file sizes so if using a 1200 dpi scan setting the file may be too big for Corel Trace. Also, Corel Draw does not like to load large files with thousands of nodes. You may have to experiment with these settings on large files to determine the amount of nodes that can be successfully loaded.
Author’s URL: Scott Fresener – https://mrroggers.wordpress.com/2008/03/21/who-is-scott-fresener/