ThomasD said:
Let's say I need to print out the photo, does increasing the dpi from 72 to 300 affect the quality of the picture?
Basically 72 dpi is about the general resolution for looking at the picture on your PC screen only. Which in most cases is fine on your PC and can look pretty sharp especially when certain software also has specially feature to blend the pixels to give it an enhance and more pleasant look on your screen.
But when you are printing out by way of a Colour Printer, 72 dpi is too coarse and will result in pixelation which translate into seeing a lot of jaggy lines and edges when printed out in 72dpi. By using Photoshop to change the picture's resolution from 72 to 300 dpi is not going to help the situation to improve. It is just the same bad situation only at a higher dpi only. You can take a 300dpi picture and readjust to view it on the PC by setting it to 72 dpi but never the other way around. To some extend it might help only if you take the size into consideration as well. That is about the only time maybe it can help your situation if you want to change it from 72dpi to 300dpi.
For example I have a picture that is 72dpi and it's size is about 24inches by 36 inches. Now you might already know those sizes does not make sense much on the PC monitor as your program will scale it down to fit your PC screen. In the real world outside the computer if you do try to print the picture at it's given value of 24x26 inches and AT 72dpi...you will find the picture would look really bad!..as there will be a lot of jaggy pixels. Now at this point you might say...okay, let's increase the dpi from 72dpi to 300 dpi that should solve it yes? Since the printer can print at 300 dpi too. Nope! Increase the the resolution from 72 to 300dpi just increase the SIZE of your picture file from say 2mb to maybe 8mb! but not the quality. The concept is very simple in graphic sense. A big picture can be shrink and it will still be fine and sharp but you can not take a small picture and increase it size and get MORE details out of it. Your picture must in the first place contain enough details and information so that it may be enlarge and still give you all those details missing when it was a small picture. Problem is those details are not like magic and pop out of no where.
Don't believe all that BS in the movies where you see some super spy or some army defense using a power camera or satellite camera to shoot an image photo and then they bring it to some lab where they would look at the picture and then have the ability to zoom in tight to some blur looking area of a print and then add more resolution to it or enhance it with a computer program so that missing or blurry details actually start to appear. The truth is if your original picture...film or digital lacks the details to begin with...there is no way you could ever get more out of it. No technology is that smart to be able to predict or manufacture it. The only way that can be true is if the designer or artist paint the image!
So how and when can you actually set the resolution from 72 dpi to 300dpi and get some "quality" out of it? Well I would not say quality but I would say the picture will look more acceptable and sharp since you will also be reducing it's size. SO getting back to my above example of 24 x 36inches at 72dpi. I will now choose say to print that picture in 8x10 print size. So I will use Photoshop to change the picture size. I will choose 300 dpi and select 8x10inche for the new size.( see again it is about reduction and using a smaller image size) Now with the new size it looks fine. In truth nobody really would print 72 dpi on their A4 printer right. Usually folk or software will scale it down to A4, maybe regular 3R, 4R or 10R. The PC might actually select 300dpi once it rescale it down to one of those sizes I just mentioned. But when would this situation not be workable? It is when the size is already 3R for example and the dpi is already at 72. You can print it out as 3R size but the quality will be very bad as the dpi is too coarse for printing and the printer will print it pixel for pixel in size! In that situation, trying to change the dpi from 72 to 300 but keeping it at 3R size will not make a difference. It just use bigger print size dots to preproduce those same 72dpi dots on your 3R size picture. It is abit hard to explain it but I hope roughly it gives you abit more idea as to why changing from 72dpi to 300 dpi in most situation will not make a difference in the final printing.
That is why when designers do design production or photo shoot, we try to get the graphic done in as higher a resolution and size as it allows. And when we know the photo we shoot will be use to make larger sharp poster and other large scale prints later on, we will try to use medium format nagatives or those larger format camera to produce those large negative that can hold more details and resolution. So that there is flexibility for reproduction work later on.
Just my two cents...
