tracing a jpg of a paper upholstery pattern

Question

Hi there,I wish to use Illustrator to convert my paper patterns (of car seat components) to SVG files.I have photographed each of the pattern elements on a fixed background (my cutting mat) and now wish to load them into AI in order to trace them.I have a scale line on each item for sizing.My question is, how do I ensure my jpg is presented at the correct size prior to tracing the pattern profile.I.e. how do I set it to full scale prior to tracing.thanksDave Hickman

Jacob Bugge · Accepted Answer

Dave,As I (mis)understand it, you could just scale the final traced pattern element since everything will be vector; and by the way it will (almost) undoubtedly be better to trace by redrawing on top of the locked image.But if you wish to start by getting the image at the exact size to start with, you may:1) Place the image at an obviously larger scale than the one desired,2) With the Line Segment Tool ClickDrag between the endpoints of the scale line on the image, then Click an empty spot with the Line Segment Tool and copy the Length (deselect in the box and ClickDrag),3) Select both 1) and 2) and Object>Transform>Scale, then in the Uniform box delete the 100 and insert the true scale line length multiplied by 100 (you may add two zeroes or move the decimal spot two places to the right) then add / (divide) followed by the copied value from 2 (without the unit) and press Enter.This should give you the exact desired size. You can make sure by determining the new length of the scale line and seeing that it is the true one.

Peter Villevoye · Answer

The camera doesn't know the size of what you're taking a picture of, so any image will need some reference to the size of the object. That's why you did it right by using a scale in your photos !

JPEGs are very vague about their measured size. The only thing you can be certain of is their number of pixels in width and height. Any other information like a dpi setting (which might be indicative of the size) is often absent, or ignored by other applications if present. Fortunately, Illustrator, Photoshop, and InDesign do try to interpret the dpi setting as an expected image size.

So an image of 72 x 72 pixels at a 72 dpi setting will yield an image of 1 inch (2,54 cm), if placed by clicking (not dragging). An image of 72 x 72 pixels at 144 dpi will be shown as an image of half an inch.

But then again, the original size of the photographed object or the image is not known by the camera, nor the resulting JPEG.

Scanners on the other hand are capable of knowing the size of the scanned object, and often include a proper dpi setting (hence size) in the JPEG file.

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