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Why You Should Only Use JPEGS for Photographs

When it comes to formats for exchanging files one of the more common formats that we use is JPEGS. JPEGS are good because most people can create them, the file size is small and when you say JPEG to someone they know what you are talking about. The problem with JPEGs is that they are good for photos but not so good for logos or other so called line art type images. The big problem with JPEGS is that they typically save the files with Anti Aliasing on. Anti Aliasing is basically trying to eliminate the “Stair Stepping” that occurs between the edge of an image and the background of the image. For a black and white image you will get subtle shades of gray that will go either darker or lighter depending on the colour of the logo and the colour of the background. To see anti aliasing at work in CorelDraw you can go to VIEW and look at your logo in Normal (non anti aliased) and Enhanced (anti aliased). So what is happening is that we are trying to be able to see the image clearer on the screen. And this is the important thing to remember here is on the screen. Not on the printer or on the laser. When it comes to the best image I suggest for a logo that is being a tiff, or bmp or eps or PDF. Just make sure that someone has not taken a JPEG and just saved it as this format. This does not work.

Here is our Test Image

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Here is an image that I used in a previous lesson. It is a JPEG image of a legend plate. Again, this was probably a photograph so this is why it is a JPEG. Most cameras are going to produce a JPEG for the output photos and because they are JPEGs they may be aliased. Also remember that if you export an image for the web because it is going to be seen on a monitor it will be anti aliased. This tends to be the default setup so turn it off if you are going to send a JPEG to someone that is not going to be seen on the web.

Anita Aliasing Up Close

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Here is a zoom of the edge of a part of the legend plate. As you can see because then we are going from red to white the edges will go dark gray to light gray. Remember your laser will engrave the light grays in an image. You may not see this on wood, but you might see it on black brass coated steel.

Our Image Converted to Gray

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Here is our image converted to gray. This makes it a little bit easier to see

Here is a Different Zoom

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Here is a zoomed out view. You can see the “shading” that is going on.

Convert Our Image to Black and White

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One way to create crisper text is to convert the text to black and white. Go to BITMAPS (1) | MODE (2) | BLACK AND WHITE (3).

Select Line Art

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From the Pull Down Menu select “Line Art” (1). The left window is your original window (2) and the right window is the preview window (3). The Threshold allows us to darken or light the image.

Threshold Setting

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The default setting is 128. If I increase the number the image becomes bigger as some of the darker shades of gray become black. If I make the number less the lighter shades of gray become white.

Converted to Black and White

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You can see the stair steeping is very pronounced at the edges of the image.

Zoomed in

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To see further how bad the stair stepping is I have zoomed in to see it. You can see the jaggiesness of the edges. The quality of our engraving is not going to be good.

Vector Image

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Now you may not think that the previous image was that bad. Well here is a vector image of the legend plate. As you can see the quality is perfect. Now this is not fair as the laser converts this to a bitmap. So let us convert it to a bitmap.

Convert the Vector Image to a Bitmap

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To do what the laser does in terms of converting the vector image to a raster or bitmap image select the vector image. Go to BITMAP (1) | CONVERT TO BITMAP (2).

Convert to Bitmap

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From within the dialog box make sure that Dithered (1), Apply ICC Profile (2) and Anti- Aliasing (3) are unchecked. The Colour is Black and White (4), the resolution can stay at 300 as the file size is minimal (6). Click OK (7).

Vector Image converted to Black and White

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As you can see the quality of the edge is better than the original file we where working on. The edges are very clean. It shows you that vector graphics are always the best to use when it comes to engraving.

What about if we Trace the Image

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Seeing the legend plate needs to be cleaned up converting it to vectors amy help. One of the great features in CorelDraw is the ability to convert a bitmap image into a vector object. When it comes to editing a line drawing such as the legend plate with issues working in vectors is easier. We can use this technique with the legend plate.

Select Line Art from the Trace Command

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Select the image. Now go to TRACE BITMAP (1) OUTLINE TRACE (2) LINE ART (3).

Set to WireFrame Overlay

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I like to work in wireframe overlay when I am comparing the trace to the original image. Set the transparency to 80.

Line Art Settings

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The default settings for the Line Art setting are all the way on the Detail (1). Smoothing is set to 25 (2). The Corner Smoothness is set to 0 (3).

Here is the Trace Of the Legend Plate in The Trace Command

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You can see that the trace is actually pretty good. The red line indicates the trace.

Legend Plate Traced

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Here is the legend plate traced. YOu can see that a little work needs to be done on the notch and the text needs to be deleted out.

Here is the Legend Plate

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I did a 2 minute cleanup and we have a pretty good replica of the original legend plate in Vector format.

Look at the Another Example

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I just got a request from a customer to help them with this logo. Another Web image JPEG. Notice the aliasing that is being done around the edges.

When it comes to formats for exchanging files one of the more common formats that we use is JPEGS. JPEGS are good because most people can create them, the file size is small and when you say JPEG to someone they know what you are talking about. The problem with JPEGs is that they are good for photos but not so good for logos or other so called line art type images. The big problem with JPEGS is that they typically save the files with Anti Aliasing on. Anti Aliasing is basically trying to eliminate the "Stair Stepping" that occurs…

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