Author Topic: How should I set up photoshop to get a proper size?  (Read 1649 times)

Network23

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How should I set up photoshop to get a proper size?
« on: April 18, 2018, 07:58:10 PM »
I am making square coasters.  In Photoshop I made a 4in x 4in square at 300DPI.
When I open it in T2 I have to resize it to 101.6mm

Is there some settings I should have so I do not have to adjust the size in T2?
Thanks.

ggallant571

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Re: How should I set up photoshop to get a proper size?
« Reply #1 on: April 18, 2018, 08:52:29 PM »
For 0.1mm resolution I scale everything to 254 DPI.

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Network23

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Re: How should I set up photoshop to get a proper size?
« Reply #2 on: April 18, 2018, 09:29:58 PM »
Thanks. Will give that a try.

ianchia

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Re: How should I set up photoshop to get a proper size?
« Reply #3 on: April 19, 2018, 04:53:15 AM »
@Zax, maybe this 0.1mm=254dpi in Photoshop, GIMP, Illustrator bitmap export etc (and 0.05mm=508dpi, 0.2mm=127dpi) should be in the T2Laser manual? It comes up often enough and I was also one of the people confused that you helped out on the forum. Unless it already is and I missed it?

Best,

- Ian
« Last Edit: April 19, 2018, 04:57:41 AM by ianchia »

Zax

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Re: How should I set up photoshop to get a proper size?
« Reply #4 on: April 19, 2018, 05:07:16 AM »
I do have 0.1 = 10 lines per mm or 254 DPI in the manual, under Resolution but could probably expand on it.

One issue I get a lot is that people think because they set an image to a physical size in their editor it will engrave at that, not understanding that raster (image) formats do not have any real world sizes and are only pixels.

The simplest way to determine size is using pixels, just multiply the pixels by the resolution. So if you have 1000 pixels and use 0.1 resolution it will be 1000 X 0.1 = 100 mm or at 0.15 resolution = 150 mm.

ianchia

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Re: How should I set up photoshop to get a proper size?
« Reply #5 on: April 19, 2018, 05:39:32 AM »
Hi Zax,

The issue with not correctly comprehending the manual is that in Photoshop, you can set the DPI to different values depending on the output media.

So for example, printing magazines might be 200 DPI.

A laser paper printer might be 600 DPI.

Or you might send 300DPI to a large format printer.

The imageís pixel size and resolutions are not tied to each other. I can have a 300x200 pixel image at 150DPI or a 300x200 pixel image at 254DPI.

And then we have screen devices which are PPI (pixels per inch) like iOS devices which typically are 326/401/458. And these are always *inches*. Ugh.

And then in Illustrator (I donít know much about Inkscape), the physical size is totally independent since itís just vectors. You setup a physical size for the artboard canvas without any DPI and you just pick a DPI if/when you export to a bitmap format if thatís what youíre after, or the vector PDF/EPS/SVG is based on your vectorís physical dimensions and DPI is never asked for.

So itís kinda confusing if thereís not a hold-your-hand explanation for newbies (like myself not that long ago) where we translate pixels to **millimeters** in T2Laser. It logically makes sense but itís definitely not intuitive.

Does that make sense how folk might get confused?

- Ian
« Last Edit: April 19, 2018, 05:41:51 AM by ianchia »

ianchia

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Re: How should I set up photoshop to get a proper size?
« Reply #6 on: April 19, 2018, 05:49:38 AM »
Oh, and a really obvious note that vector shapes are not affected by T2Laserís resolution setting. Unless they are and I missed that as well? (-;

- Ian

Zax

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Re: How should I set up photoshop to get a proper size?
« Reply #7 on: April 19, 2018, 08:24:53 AM »
I do not agree with your statement "imageís pixel size and resolutions are not tied to each other", in fact the opposite is true. The dpi setting is directly translated to the pixels, it has to be, whether in the file or later by interpolation by the printing or display method.

If you create a 1" square image at 254 dpi it will generate a 254 x 254 pixel image, now change that to 300 dpi and Photoshop will scale up the image to 300 x 300 pixels. It's really that simple.

You are correct, vector files are different and T2Laser reads the size directly from the file. The exception is AutoCAD has now decided to use a dimensionless format.

ianchia

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Re: How should I set up photoshop to get a proper size?
« Reply #8 on: April 19, 2018, 04:24:54 PM »
I do not agree with your statement "imageís pixel size and resolutions are not tied to each other", in fact the opposite is true. The dpi setting is directly translated to the pixels, it has to be, whether in the file or later by interpolation by the printing or display method.

Well, yes and no. It was loosely worded on my part and I apologize - that's what I get for posting just before bed. Over the years, I have spent a bit of time explaining to people display resolution vs print resolution vs media resolution (and you probably have as well.) If it was easy, the situation wouldn't exist where people are upset that their printouts are blurry on paper when they looked fine on their device screens where the images were downloaded.

I'm just trying to help clarify how one might explain this resolution thingy to people who are new to laser engraving, new to image editing, and have no idea that the output media type might also affect the equation. Although a fact or equation might be simple, sometimes understanding is quite tricky.

Let's take the attached PNG for example. It's a 500x500 pixel, 50x50mm, 254 Pixels per inch, PNG.

In Photoshop, if I select Image > Image Size, the dialog box looks like this.



Following your statement where the "dpi setting is directly translated to the pixels" - I'll change the Pixels/inch setting from 254 to 300 and voila! Your statement proves true. The image is automatically adjusted by Photoshop to 591x591 pixels.


 
But...

Now I edit the pixel dimensions for width and height back to 500 x 500. Now my resolution is 300 Pixels per inch, and the image's pixel dimensions are again 500x500, but my document *physical* size is 42.33x42.33mm.



We both understand that it's because the pixels are now physically smaller, but that's not generally obvious to someone new to this. (eg. "Pixels can be smaller? I thought it was just a dot on the screen...") It *could* be seen that I've retained the same 500x500 pixel dimensions for both images and yet the resolution setting is different. That's what I was trying to say originally (badly.)

Yes - the "dpi setting is directly translated to the pixels, it has to be, whether in the file or later by interpolation by the printing or display method" statement is absolutely true. And yet, kinda confusing... because one can keep the same pixel size AND change the dpi/ppi setting. Yes, it's obvious that the "document size" changes as a result of this, but unless folk have a design or print background, what does that mean? I imagine that a very common use-case might be people downloading raster images off the web, and then try to engrave - and those images might typically be 72 or 96 dpi. I can even imagine that they'll bypass any image editing program, load them straight into T2Laser, set the resolution to 0.1 and output size to be 6x4 inches etc, only to be disappointed that their engraving is so blurry.

And then we get to the output media's native resolution. It's not immediately intuitive for a person new to laser engraving that the type of material being engraved has a natural limitation on resolution. eg. slate has a low output resolution, acrylic and mirror has a high (254 or higher?) resolution, different types of paper have different resolutions (254dpi for origami, but maybe 120-ish for watercolour paper), MDF might have a 200dpi resolution and different wood grains densities and even the direction of the grain will affect the mid-to-low resolution.

I don't know if you want lengthy stuff like this in the T2Laser manual. I figure it would make a better customer experience if there was a explanation or tutorial so that it was less confusing up front, particularly to newcomers of laser engraving with no print or design experience.

All the best,

- Ian


« Last Edit: April 19, 2018, 04:35:36 PM by ianchia »

Zax

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Re: How should I set up photoshop to get a proper size?
« Reply #9 on: April 19, 2018, 05:14:16 PM »
Now I understand why your results are so impressive  ;)