Importing bitmap is auto-sizing?

[jginvc]

I am trying to engrave some simple dog tags and I scanned a 1:1 image of the blank on my scanner (which imports it as a rectangle document) in order to trace the bitmap to get the size correct. But it is auto-scaling the bitmap to whatever size my job is! I don't remember it doing this before, but maybe I haven't actually tried this exact task before. But why would it auto-scale to fill the job size?

[Adrian]

It always has done up to a point. It depends on how big the original bitmap is.

If you know the size of it then either import to a job the size of the image or use the Size tool after import.

[jginvc]

Shoot, kind of defeats the purpose. I do this all the time with my PCB cad program. Oh well, I ended up just drawing it by hand using measurements I took with my calipers. Took a lot longer but it came out ok.

[adze_cnc]

I scanned a 1:1 image of the blank on my scanner

An image file is never "1:1" really. An image file is only x by y pixels. It's up to software to determine how those pixels correspond to measurements.

For example: If you scan an image of a square that measures 1" at 300ppi (pixel per inch) to a JPEG file you will get a file that is 300 x 300. If you then print that on a printer at 600dpi you will end up with a 1/2" square on paper.

If you view that same image on a Windows machine (whose video is 96ppi) you will get a square that is 3.125" as measured on screen. On a 72ppi Macintosh it will be 4.1666".

Just this morning I imported a 408 x 1098 pixel JPG file into VCarve. There was no resolution specified in the file (typical for JPEGs) so it was imported at Windows' default 96ppi giving an image in VCarve as 4.25" x 11.4375". A TIFF would have been much better.

Because my job size was larger than those measurements the file imported "at size". Had my job size been, say 3" x 8" the imported JPEG file would have been scaled down to fit the job size—which is, I expect, what you are seeing.

If you really want your image to import "at size" then temporarily make your job size larger and then resize the job after import.

[jginvc]

Yes I understand that, I was stating that rather than taking a picture of something and then scaling it by placing a ruler next to the object to scale it accurately. When I design chassis for my PCBs I can use a scanner which imports it at the correct pixels/in resolution based on the meta data. I guess my other CAD software is just a little more clever.