brook

Images from my digital camera that are viewed in PhotoShop always indicate a resolution of 72 ppi in the Image Size dialog box. It doesn?t matter if the images were taken at 1 mega pixel, 2M or 3M, they all have a resolution of 72 ppi indicated in the Image Size dialog box. I assume that is because most monitors screen resolution is 72 ppi. Is this true? Also, if I want to print a photo at 300 dpi with an inkjet, do I need to change this 72 ppi setting to 300 dpi? What about the printers software, does that change the dpi setting when I select best print as opposed to normal print? All these settings, so confusing??

jpfitness

that's a weird one Brook [stuned] and I have never noticed or seen that before........ where did you look to see that it was 72dpi?
When I open my images they open at what ever dpi the photos were taken at, I wonder if it is a prefrence thing?
just try this for an excerse....... open a photo, select all, edit/copy, file/new........ when this box opens it will tell you the size and resulution of the image that you have copied, let us know what it says
sfm

Bacardi

Ahh, never mind, as this is not important. This 72 dates from the beginnings of real puter days because Apple printers used them, and also because in the print world 72 means 12 times 6 points. Photoshop still sets type in points. you can check under "preferences". You can still choose between the "real" points, 72,27 and the postscript simplification of 72.


What is important is Image>Image Size. There you can set to piels so you can know exactly how many pixels you have at your disposition. Then, when you uncheck "resample" and change the number of pixels that will fit in an inch, the final size will of course change, but the quality will increase when you use more pixels to define each inch.
For normal desktop printers, even photo quality, you will not need more than 150-200 pixels per inch. The rest is really pure overkill. 300 can be used for professional offset printing, but it is less sharp than 266ppi.

My way of looking at things is: say you have a size of 2400x1800 pixels.
Try out a print at 150 and 200 pixels per inch, and look at the quality. The main difference will be that at 150 the size will be 16x12inch, and at 200 it will be smaller, namely 12x9 inch. For most normal work and quality, 150 will do. But you can play with the ppi and set to, say 178 if you want to change the printed size without resampling. What will happen is that your printer software will do the resampling for you.

Whether the colours will be correctdepends on something else...

wbiss

Erik, you beat me to it! Great explanation! [righton]

brook, your photo size dialogue box shows at 72 ppi (pixels per inch) because that is the standard jpeg resolution of digital cameras. Do not confuse dpi with ppi (a common mistake) because dpi refers to "dots per inch", in the case of print.

When it comes to "print" (refer to the image below) by decreasing the image size (leave the 'resample' box unchecked, you automatically increase the ppi. 300 ppi seems to be "optimum" for most printers (and even "overkill" as Erik has mentioned) but you can play and see what kind of results you get at 150-200. You will notice that when you resize for print, your file size stays unchanged. No loss of data means a higher quality output!

ladyfinger007

Excellent explanation both of you! :}

Some (hi-end) users reported that for some ink jet printers, it is good to work on derivates from the resolution.

Say your printer can make 2880 dpi (max theorical resolution of the smallests dots of ink) it is good to make your files at 288 ppi (pixels per inch) or 360 ppi instead of the "rule of thumb" of 300 ppi (in most cases, there would be an "uneven" interpolation) IIRC, they were talking about the professional range of Epson printers (the 2200, the 7600 and 9600...) Now, it's up to you to test what works best for you!