Help with screenshots

Using an image editor (like Photoshop) you can swap resolution for size.

i.e. if you take a screenshot at 2545x1358 pixels at 72dpi (about 90cm), you can convert that to 300dpi in an image editor, but the physical pixel dimensions get's smaller - it would come out at around 21cm.

Dependant on how big you need it, this may be enough.

if you need it bigger than 21cm (in the example), then the image editor would have to sample up pixels and the image may blur.

macOS offers only this:

1. Press Command-Shift-4 which will change the cursor to crosshairs.
2. Hold down the mouse button and use the crosshairs to select the part of the screen you wish to capture.
3. Release the mouse button and the image will be saved to your Desktop.

1. Press Command-Shift-5 to access the advanced screenshot controls.
2. A sizable rectangle will appear to select whatever part of the screen you wish to snap.
3. A floating control pallet is on the bottom left from which you can select various options.
4. Images can be saved on the Desktop.

The resolution should be the same as your screen's resolution.

You can't take a 300 dpi screen shot of a screen that can't display 300 dpi. You could convert the screen shot to 300 dpi but of course you have nothing to gain.

No. The easiest way to explain is this. Let's say you had a 1x1 ppi screen, you color it black. Now you convert it to 4x4 dpi, four times the resolution. However, there's no more information so it would still look like a 1x1 black square and have no more detail.

Just to add, as far as any part of your post being irrelevant, the question was how to take a 300 dpi screen shot which is not possible no matter what you've had to say.

The best way to think about this is that pixel dimensions and size are just a way of showing the amount of information in an image, they are 2 pieces of information and they are linked intrinsically.

Say an image is 100x100 pixels at 100dpi, if you increase the resolution by 3 to 300dpi, the pixel size of the image goes down by 3.

Increase dpi, decrease pixel size.

Increase pixel size, decrease dpi.

You can of course resample an image up and override this, but the software you use has to get that information from somewhere, it can't create detail that wasn't there in the first place.

So it uses interpolation (comparing 2 pixels side by side and averaging between them) to create new pixels, which if you push that too far, simply blurs the image.

Your Mac is always 109 dpi regardless of what resolution you set it at. However, 2560x1440 is the highest resolution it can display so it would look the best on screen and show as much detail on screen as it can.

Take any 72 dpi image you like, convert it to 300 dpi without changing its dimensions in Preview. It will look exactly the same. However, if you enlarge an image enough it will start looking pixelated. None of which has anything to do with this thread.

"None of which has anything to do with this thread"

Yes it has - the poster asked whether he can take screenshots at 300dpi but his display would only capture at 109dpi and whether he could do anything to the image to get it to 300dpi.

I said that you can increase it to 300dpi but it would decrease the physical pixel dims of the image. If the poster wants to increase it to 300dpi and keep the same dimensions, then the image will blur.

I fail to see where any part of my post is incorrect or irrelevant.

So there's no way to get a higher resolution screenshot on Mojave? What about a developer tool like Quartz Debug that works on older iOS? Is there a third party program that enables a higher resolution screenshot? Or, finally, must I have a graphics card newer than NVDIA GeForce GTX 775M 2048 MB or a newer screen than my iMac (27-inch, Late 2013)?

Thank you for a response

Given my equipment and graphics card (above), Is my display now 300 dpi? Under System preferences/Display, every time I open it, it shows default display, even after I've checked Scaled 2540X1440. Is this the default? I'm considering buying a new iMac. Is there any equipment that delivers more than 300 dpi?

So if the screenshot is 2545X1358, or 1600X900, the screenshot dpt does not change. But won't the 2545 look better if the size of both remain the same? I am putting these screens shots in videos, some of which I'll blow up.

Thank you all. Very insightful discussion. Last question: If I took two screenshots of the same image but only changed the ppi from 109 to 218 (using two different iMacs), will the image of the 218 look sharper/clearer?

The ppi of a 27" 5K iMac and iMac Pro is 218. Your iMac is 109.

Actually you can change the resolution without changing the size. You just don't gain anything in doing so.