Counting Pixels using Gimp?

Discussion in 'Off-Topic' started by spinnaker, Jan 30, 2016.

  1. spinnaker

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    Oct 29, 2009
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    I can across this article regarding calibrating a bit for etching.

    http://phk.freebsd.dk/CncPcb/calibrate.html

    I guess all bits are not created equal. And it sort of makes sense that the width of the bit will change slightly the deeper it goes.

    The author suggests, scanning your etched board and counting pixels to get the width. I understand this can be done in Gimp but I have no idea how that would be done.

    Can anyone explain step by step? I almost know nothing about gimp.
     
  2. ISB123

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    You use the measure tool which measures the distance in pixels, after that you just convert pixel to mm to get the results.
     
  3. Wendy

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    I standardize everything to 600 px / in for the laser printer. I go through this same dang learning curve every stinking time!

    If you save the PCB file as a graphic (I use .gif) it will come up in windows when you hover over the file.

    I am fresh on the problem because I am in the process of making a board now.
     
  4. spinnaker

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    I see, the hover tool, I can draw a line. But that is it. Can't figure out how to use it. The line is never ending for me. I have tried esc, enter, click. It keeps wanting to draw the line.
     
  5. spinnaker

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    Not following you at all. How are you measuring the width of a trace?
     
  6. ISB123

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    You have to hold and drag it across the object you want to measure. After that on bottom part of GIMP's GUI it should display the measured value.

    Capture.PNG
     
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  7. Wendy

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    I use paint for basic editing. Each pixel is 1/600 of an inch. or 1/60 for .1". When you use select (I believe something similar exists for Gimp) it will give the box size in pixels. I use simple math. So if a trace is 5 pixels wide then it is 5/600 (8.3 mils) wide.

    I don't use Gimp for editing, I'm too used to paint. But Gimp is marvelous for converting file types (.pdf to .gif) and for printing to scale. Since the maximum resolution for most laser printers is 600 DPI that is what I use.
     
  8. spinnaker

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    Got it. Not sure what I was using before but it was not the measuring tool. Thanks
     
  9. spinnaker

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    Got it. Makes sense now. So if you know your image was scanned in at 600 dpi then that is 600 pixels to the inch. Makes sense now. :)


    Are you milling PCBs? Or just using this method to calibrate other pcb creation methods?
     
  10. joeyd999

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    The scale image tool will allow you to set the resolution and size of the image (in any of a number of possible units), if this helps.
     
  11. Wendy

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    Milling PCB is one of those things I would dearly love to learn. That or drilling a constellation of holes using one of the small scale machines. We have several at maker space that I look at wistfully some days. It will happen, but don't know when. Just drilling the holes would be a huge help. Right now I'm still using the toner transfer technique.
     
  12. spinnaker

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    I agree. I am struggling right now getting the milling right. My traces and pads are coming out smaller than they should be, I think. The issue is getting all of the settings right. So far I am not happy with the results. Toner transfer turns out a much nicer board.

    But doing drilling only would be a challenge too. The problem is matching up the traces with the drill holes. Basically what you do is to mill the traces. Before you do, you pick a x/y spot on your board as the starting location. You mill the board then switch to the drilling job. You don't reset the x/y zero point, that way the drill holes are lined up automatically. If you don't mill then you need to line up the drill spots manually. I have already done it. I messed up by zeroing x/y before getting to drilling and I had to line things up manually. It was tedious. The good news is that when you get one whole lined up, they are all lined up.
     
  13. Wendy

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    If you have an accurate constellation of holes you would drill them on the blank board, then do the toner transfer. Alignment would be much easier then, I have a personal pad pattern I like that makes this easier (see Making Gerber Files). Sounds like we are working on the same problems coming from two different angles.

    I'm following up and a different transfer technique that has been suggested, using a smooth sheet of 1/4" aluminum on a sandwich grill and a rolling pin, It has a temperature control among other things. I'll post it in Completed projects if I get it to work the way I want.
     
  14. spinnaker

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    Ah that is a good idea. Think backward. :)

    Sounds like no reason that would not work. A translucent transfer material would make things a bit easier. I use waxpaper so that would work.

    I use a laminator for transferring the toner. Works fairly well though even with it, it can be hit or miss.
     
  15. joeyd999

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    Actually, this is 'forward thinking', in the sense that, in an automated fab, holes are drilled and plated prior to etching.
     
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