Understanding Resolution
How Many Pixels (or how much resolution) do I need? If you ask people new to digital imaging how big a pixel is they’ll come up with a wide variety of answers. Experienced digital folks know that the correct answer is, “it depends”.
The more pixels you have, the larger the file size, and the greater the potential to print the image in larger sizes. Like a mosaic in an old church, the more tiles there are, the more detail there is in the image. A 2-foot square mosaic that was created with 2-inch tiles will have less detail than one of the same overall size that was created with quarter-inch tiles. So, an image with 1200 x 1600 a total of 3.2 megapixels will not have as much detail and sharpness as say an image with 1944 x 2592 a total of 5 megapixels.
In terms of how this translates to a digital camera, for example, my Canon 20D can capture up to a maximum of 2336 pixels by 3504 pixels. 2336 x 3504= 8,185,344. So, this camera is an 8.2 Megapixel camera. Let’s go to Photoshop to see how the camera’s resolution affects the file size. Go to File> New. For the Width type in 2336. For the Height type in 3504. For Resolution type in 72. Color Mode: Select: RGB Color. Notice the Image file size is 23.4MB. Now for a 5 Megapixel camera like the Canon G-5, it’s pixel dimensions are 1944 x 2592= 5,038,848. Now change the dimensions in the window. For the Width type in 1944. For the Height type in 2592. For Resolution type in 72. Color Mode: Select: RGB Color. Notice this Image file size is smaller at 14.4MB.
In this instance, if you want to print, then BIGGER IS BETTER! The larger the file size, the more you will be able to do with the image later. The term “File Size” is all about how much information that is captured with your camera for that shot, in terms of how much memory (RAM) it occupies. So, in order to answer the question of “How many pixels or how much resolution do I need?” it ultimately depends on what you want to end up doing with the image. More on this to follow.
How Big is a Pixel? Again, the answer is it depends.
A pixel size depends on two factors; how many pixels there are in each row and column of an image, and how many inches you tell an output device that image is going to be on each side. In other words, a pixel has no set dimension until you tell it what size it is relative to some output device.
Assuming the number of pixels remains constant, the pixels per inch, and the resolution- will change as the size of the print or displayed image increases or decreases. For example, as you increase the print size (say from a 4x5 to an 8x10), the same total number of pixels spread out to fill a bigger space. Each pixel has to increase in size, which decreases the resolution, and makes the image appear less sharp than a smaller print of the same size.
You have to know where you’re going to output before you start. To get maximum quality with digital images, you must know where you are going (in terms of output) before you capture and when you are going to output a file to a particular device.
Resolution for On-Screen
When you’re working on images that will be presented on-screen (websites, PowerPoint, e-mail, etc.), then you don’t need very many pixels, because the screen is a relatively ”low-resolution” environment. All computer screens have the same number of screen pixels every inch: 72 pixels per inch, where every linear inch of screen has 72 pixels on it. If you think in terms of your screen’s native resolution (with Windows, it’s usually the default of 800x600 pixels; on the Mac, the default is 1024x768 pixels.) That’s not very many pixels: 1024 x 768 = 786,432 or less than one (1) megapixel.
Website’s images are typically much smaller than maximum screen resolution, usually on the order of only a few hundred pixels on each side. If you look, say, at the main image on the front page of the COD website, you’ll find that it’s typical around 500 by 200 pixels. Many website images are much smaller.
Resolution for Print
Print resolution is a bit more complicated, because you have to know what resolution is needed for the printer you are sending the image to. For maximum quality laser printers, you need somewhere around 100 pixels per inch, and inkjet printers need somewhere between 150 and 200 pixels per inch, and consumer lab printers (like Costco) are around 320 pixels per inch.
So, if you want to make an 8x10 inch print, and you want to print it on an inkjet printer that should have 200 pixels per inch, you’ll have to do the math: 10 inches x 200 pixels per inch = 2000 pixels AND 8 inches x 200 pixels per inch = 1600 pixels. So, you’ll need an image that is around 2000x1600 pixels. So, if you have 3,200,000 pixels (or 3.2 megapixels) you have enough for an 8x10 image on that printer. Obviously, if you wanted to print a smaller print, you wouldn’t need as many pixels.
Let’s look at some examples and use Photoshop to do the simple calculations for us to see how the number of pixels affects the file size and the image size.
Again using a Canon 20D I can capture up to a maximum of 2336 pixels by 3504 pixels. 2336 x 3504= 8,185,344. Go to File> New. Type in the Width: 2336 pixels. Type in the Height: 3504 pixels. Type in Resolution: 72. Color Mode: Select: RGB Color. Click: OK. Now go to Image> Image Size and you will see that at a Resolution of 72 (good for on-screen viewing only) I can get an image size of approx. 32 x 48 inches. Notice the Image file size is 23.4MB. On the bottom of the Image Size Window “Check On: Constrain Proportions”. Make sure Scale Styles and Resample Image are Off”. Now change the resolution to 150ppi (to make a print on our inkjet printer) and notice that now I can only make a print up to 15x23 inches. Notice that the Image file size is 23.4MB. Finally, change the resolution to 320ppi (to make a print at what Costco recommends) and notice now I can only make a print up to 7x11 (significantly smaller than where we started). That is why the more pixels you have the better, if you want to make bigger prints. Notice that the Image file size is still at 23.4MB. Why is this? The file size won’t change because the # of actual pixels hasn’t changed (there are still 2336x3504). The only thing that is changed is the size of the pixels and how many can fit per inch.
The bottom line is that you have to know where you are going to output before you start!
The more pixels you have, the larger the file size, and the greater the potential to print the image in larger sizes. Like a mosaic in an old church, the more tiles there are, the more detail there is in the image. A 2-foot square mosaic that was created with 2-inch tiles will have less detail than one of the same overall size that was created with quarter-inch tiles. So, an image with 1200 x 1600 a total of 3.2 megapixels will not have as much detail and sharpness as say an image with 1944 x 2592 a total of 5 megapixels.
In terms of how this translates to a digital camera, for example, my Canon 20D can capture up to a maximum of 2336 pixels by 3504 pixels. 2336 x 3504= 8,185,344. So, this camera is an 8.2 Megapixel camera. Let’s go to Photoshop to see how the camera’s resolution affects the file size. Go to File> New. For the Width type in 2336. For the Height type in 3504. For Resolution type in 72. Color Mode: Select: RGB Color. Notice the Image file size is 23.4MB. Now for a 5 Megapixel camera like the Canon G-5, it’s pixel dimensions are 1944 x 2592= 5,038,848. Now change the dimensions in the window. For the Width type in 1944. For the Height type in 2592. For Resolution type in 72. Color Mode: Select: RGB Color. Notice this Image file size is smaller at 14.4MB.
In this instance, if you want to print, then BIGGER IS BETTER! The larger the file size, the more you will be able to do with the image later. The term “File Size” is all about how much information that is captured with your camera for that shot, in terms of how much memory (RAM) it occupies. So, in order to answer the question of “How many pixels or how much resolution do I need?” it ultimately depends on what you want to end up doing with the image. More on this to follow.
How Big is a Pixel? Again, the answer is it depends.
A pixel size depends on two factors; how many pixels there are in each row and column of an image, and how many inches you tell an output device that image is going to be on each side. In other words, a pixel has no set dimension until you tell it what size it is relative to some output device.
Assuming the number of pixels remains constant, the pixels per inch, and the resolution- will change as the size of the print or displayed image increases or decreases. For example, as you increase the print size (say from a 4x5 to an 8x10), the same total number of pixels spread out to fill a bigger space. Each pixel has to increase in size, which decreases the resolution, and makes the image appear less sharp than a smaller print of the same size.
You have to know where you’re going to output before you start. To get maximum quality with digital images, you must know where you are going (in terms of output) before you capture and when you are going to output a file to a particular device.
Resolution for On-Screen
When you’re working on images that will be presented on-screen (websites, PowerPoint, e-mail, etc.), then you don’t need very many pixels, because the screen is a relatively ”low-resolution” environment. All computer screens have the same number of screen pixels every inch: 72 pixels per inch, where every linear inch of screen has 72 pixels on it. If you think in terms of your screen’s native resolution (with Windows, it’s usually the default of 800x600 pixels; on the Mac, the default is 1024x768 pixels.) That’s not very many pixels: 1024 x 768 = 786,432 or less than one (1) megapixel.
Website’s images are typically much smaller than maximum screen resolution, usually on the order of only a few hundred pixels on each side. If you look, say, at the main image on the front page of the COD website, you’ll find that it’s typical around 500 by 200 pixels. Many website images are much smaller.
Resolution for Print
Print resolution is a bit more complicated, because you have to know what resolution is needed for the printer you are sending the image to. For maximum quality laser printers, you need somewhere around 100 pixels per inch, and inkjet printers need somewhere between 150 and 200 pixels per inch, and consumer lab printers (like Costco) are around 320 pixels per inch.
So, if you want to make an 8x10 inch print, and you want to print it on an inkjet printer that should have 200 pixels per inch, you’ll have to do the math: 10 inches x 200 pixels per inch = 2000 pixels AND 8 inches x 200 pixels per inch = 1600 pixels. So, you’ll need an image that is around 2000x1600 pixels. So, if you have 3,200,000 pixels (or 3.2 megapixels) you have enough for an 8x10 image on that printer. Obviously, if you wanted to print a smaller print, you wouldn’t need as many pixels.
Let’s look at some examples and use Photoshop to do the simple calculations for us to see how the number of pixels affects the file size and the image size.
Again using a Canon 20D I can capture up to a maximum of 2336 pixels by 3504 pixels. 2336 x 3504= 8,185,344. Go to File> New. Type in the Width: 2336 pixels. Type in the Height: 3504 pixels. Type in Resolution: 72. Color Mode: Select: RGB Color. Click: OK. Now go to Image> Image Size and you will see that at a Resolution of 72 (good for on-screen viewing only) I can get an image size of approx. 32 x 48 inches. Notice the Image file size is 23.4MB. On the bottom of the Image Size Window “Check On: Constrain Proportions”. Make sure Scale Styles and Resample Image are Off”. Now change the resolution to 150ppi (to make a print on our inkjet printer) and notice that now I can only make a print up to 15x23 inches. Notice that the Image file size is 23.4MB. Finally, change the resolution to 320ppi (to make a print at what Costco recommends) and notice now I can only make a print up to 7x11 (significantly smaller than where we started). That is why the more pixels you have the better, if you want to make bigger prints. Notice that the Image file size is still at 23.4MB. Why is this? The file size won’t change because the # of actual pixels hasn’t changed (there are still 2336x3504). The only thing that is changed is the size of the pixels and how many can fit per inch.
The bottom line is that you have to know where you are going to output before you start!