how to convert pixels in mm ?

[Andy_Bat1]

Hello everybody!

I'm making a tool in which the user specifies the size of the frame, I want to give him the opportunity to choose between units of measurement. How do I convert one unit to another? Centimeters to millimeters as I know 🙂

The calculations in my instrument produced in pixels. A user wants to place on a sheet of paper photos of a certain size in order to then cut them after printing and pasted into the frame.

This part of the script produces the  selection of the pixel size, but calculation was conducted in millimeters.

app.preferences.rulerUnits = Units.MM;


var newSelect = Array(
                   Array(Left, Top),
                   Array(Right, Top),
                   Array(Right, Bottom),
                   Array(Left, Bottom),
                   Array(Left, Top)
 );
 doc.selection.select(newSelect);

Came up with a solution, I do not know how much it is optimal - use factor

app.preferences.rulerUnits = Units.MM;
rmm = doc.width;
app.preferences.rulerUnits = Units.PIXELS;
rpix = doc.width;
var propPixMm = rpix.value/rmm.value;

[gener7]

Pixels are not physical units of measurement. They are computer data units that define a raster image.

You can have 1000 pixels and decide whether they print to 1 mm, 1 cm, or 1 meter in length. It will still be 1000 pixels.

The best way to see this is to open a file, open the Image Size box and turn resampling off.

Change the physical size and you will see the amount of pixels remain the same.

[Andy_Bat1]

My last solution is used Photoshop patameters and Photoshop factor, I'm happy ^-)

[YahorShumski]

Resolution is what connects pixels with real world. Printing standard of resolution is 300ppi, that means the 'density' of pixels is 300 pixels per inch.

[Michael_L_Hale]

When using UnitValue objects you can have it convert between unit types.

app.preferences.rulerUnits = Units.MM;// or any other unit except percent

var rmm = doc.width;

alert(rmm.as('px'));

[Andy_Bat1]

my variant (all correct):

#target photoshop

var doc = app.activeDocument ;

app.preferences.rulerUnits = Units.MM;

rmmW = doc.width.value;

app.preferences.rulerUnits = Units.PIXELS;

rpixW = doc.width.value;

var PixMm = rpixW/rmmW;

alert(rmmW +"mm / "+rpixW +"pix\n factor " + PixMm);

[pixxxelschubser]

var doc = app.activeDocument;
app.preferences.rulerUnits = Units.MM;
rmmW = doc.width.value;
app.preferences.rulerUnits = Units.PIXELS;
rpixW = doc.width.value;
var PixMm = rpixW/rmmW;
// 🙂
var WidthMM= rpixW/doc.resolution*25.4;
alert(rmmW +"mm / "+rpixW +"pix\n factor " + PixMm);
// 🙂
alert(doc.resolution+"\n"+WidthMM+" mm");

[pixxxelschubser]

@Andy_Bat1,

Did you found the best solution for you?

[Andy_Bat1]

I'm stopped on my self solution

[Michael_L_Hale]

Sorry, I was not trying to say your variant does not work. I was just pointing out how to use less code and take advantage of the UnitValue method.

[AngelOfLight-Australia]

How to Convert from Pixels to Millimeters from How to convert from pixels to millimeters « DallinJones.com

In chemistry, we studied something called dimensional analysis. Dimensional analysis is a method for converting from one unit to another. So first off we multiply the number of pixels by 1 over our DPI (in this case 300 DPI) then we multiply that by 25.4 by one inch (number of millimeters in an inch) Once everything cancels out we are left with a fairly nice, simple and easy to use formula.

mm = (pixels * 25.4) / dpi

In order to convert back from millimeters to pixels we simply reverse the formula using simple algebra.

pixels = (mm * dpi) / 25.4

There you have it. A very simple way to convert from pixels to millimeters. And then from millimeters back to pixels.