[ This article was first published in the January, 2009, issue of
Larry’s Final Cut Pro Newsletter. Click here to subscribe. ]
Thomas Kihneman, from Prime Time Advertising, writes:
Thanks for your seminars. As always, I learn new things. [In fact, during one session,] we were fighting about DPI. Here is why I often have to deal with that terminology.
When you drop an EPS image on Photoshop this is what you get.
I don’t know if there is a way to change preferences to match your way of thinking or am I just misunderstanding what that 300 means?
Larry replies: Tom, we weren’t fighting, it was a spirited discussion – and I appreciated all your questions!
DPI is a term relevant to print, where different printers and presses have differing resolutions. EPS was a format invented to meet the needs of print. They are, essentially, a mathematical formula that describes an image or font. Because EPS describes everything using math, it can be scaled to any arbitrary size, or any arbitrary resolution, very easily.
Because Photoshop tends to think in print terms, it defaults the DPI setting on imported EPS files to 300 DPI. This makes sense if you want to print your Photoshop document.
However, all video is bitmapped and fixed in resolution: 720 x 480, 1280 x 720, 1920 x 1080. Regardless of how big, or small, a screen you view the video on, the resolution of the image does not change. DPI is not relevant because as the screen gets bigger, the DPI does not increase. Each pixel simply grows bigger to fill the frame.
With video, what is important is the total number of pixels across, by the total number of pixels down. Video cares about pixel count, not DPI.
This is the direct opposite of print, where as the piece of paper to be printed gets bigger, you need more pixels to cover it.
Consequently, DPI for video is meaningless – since all video has fixed resolution, as screen size increases, all we can do is make each pixel bigger. Thus, the DPI of a 60 inch monitor is totally different than the DPI of a 9 inch monitor — yet the number of pixels in the image remains the same.
For this reason, I recommend you ignore DPI, and concentrate on the total number of pixels. It will simplify your life. In the case of importing your EPS file, set the DPI to 72.
UPDATE – Jan. 7, 2009
Don Smith, from NewsVideo.com, asks:
Your advice [to ignore DPI] prompts my question: “Doesn’t a higher DPI allow you to zoom into a small section of the picture better?”
I recently had to import a still of a young girl walking beside an elderly lady in a wheelchair and the two were holding hands. I made a move on the picture starting with a very tight close-up of their hands, then pulling out for a reveal. If the picture I started with had only the pixels across and pixels down to match a frame of video resolution and I push in to a small part of that picture, wouldn’t the result be pixelated? Is it here that DPI would come to the rescue? In the case of the two people holding hands I used a large file and thus was able to push in tight without pixelating.
Or, if I plan a push, is it that I just need to start with a picture several times the x and y pixel count of video?
Larry replies: Don, you are confusing DPI with pixel count. DPI measures the number of pixels per inch in the image – Dots Per Inch – which is meaningless when the same image is displayed on a 9-inch field monitor and a 60-inch beheamoth in the living room. By increasing DPI, what you are really doing is increasing the total number of pixels, which allows you to move around the image.
So, I stand by my advice – set DPI to 72 and stop worrying about it. Instead, concentrate on the total number of pixels across and down. As those increase, up to a point, you are able to move around and zoom into a picture.
Note: Final Cut Pro has a limit of about 4,000 pixels on any dimension. Do NOT try to force it to handle extremely large images, it will crash.