Have you just bought a new camera or smartphone and you would like to know how big you will be able to print your still pictures? Are you thinking of making a photo album with your favourite photos but you do not know with what size they will look good? Although this depends on several factors, we explain how it works in general and we give you an interactive tool so you can know it without having to use a calculator.
For the impatient, here you have the Blurbiness® Photo Size Calculator. But we recommend you read the rest of the article too.
In this article we explain:
- What is a pixel?
- What are Megapixels?
- How do I know how many pixels my photo has?
- Pixels and printing dots
- Dots per inch resolution
- Let us simplify, pixels per inch and dots per inch
- Viewing distance: the farther, the lower resolution
- More Megapixels does not mean more quality
- Not all JPEGs are equal
- The paper quality
- The photo quality
What is a pixel?
Digital images that you see on your screen are composed of tiny “squares”. Every single one of these squares can have a different color, and many tiny squares together form a picture. Pixel is how we name every one of those squares.
Pixel by pixel, we make a bigger picture. In this way, if a photo is, for instance, 1,920 pixels wide and 1,080 pixels tall, then the image is composed of 1,920 x 1,080 pixels, that is, 2,073,600 pixels in total. And it is said that the image has a resolution of 1,920 x 1,080 pixels.
What are Megapixels?
Now that you know what a pixel is, it is easy to understand what Megapixels are. A Megapixel is just a million (mega) pixels. Therefore, an image with a resolution of 4,000 x 3,000 pixels will have 12,000,000 pixels in total, which is the same as 12 Megapixels. Usually, Megapixels are abbreviated as Mpx.
How do I know how many pixels my photo has?
If you already have a photo, how do you know how many pixels it has? It is easy. We explain how to know what pixel resolution an image has in the following sections.
How to know how many pixels a photo has in Windows
If you are using Windows:
- Right click on the photo.
- Click on “Properties”.
- Click on “Details” tab. Depending on your Windows version, this tab may have a different name.
- You will see the picture dimensions in pixels under the “Image” section, for example “1280 x 1024”.
How to know how many pixels a photo has in Mac
f you are using Mac:
- Right click on the photo (or Ctrl + Left click).
- Click on “Get Info”.
- In the “More info” section you will see the picture dimensions in pixels, for example “1920 x 1080”.
How to know how many pixels a photo has in Android
If you already have a photo in your Android smartphone or tablet:
- Launch the photo gallery.
- Tap on the picture that you want.
- Press the menu button on your smartphone or tablet.
- Tap on the “Details” option in the menu that appears.
- You will see the picture width and height in pixels. For example, “Width: 2560” and “Height: 1920”, which means that your photo has a resolution of 2,560 x 1,920 pixels.
How to know how many pixels a photo has in iPhone or iPad
Unfortunately, the”Photos” application which comes with the iPhone or iPad does not have the option to show the details of one picture, at least at the moment of writing this article. However, with a very simple free app you will be able to show the pixel resolution of any photo that you have in your iPhone/iPad:
- Install the Photo EXIF Viewer free app in your iPhone or iPad.
- Launch the app.
- Tap on the “+” icon at the top right.
- Tap on “Photo Library” to choose a photo from your gallery.
- Pick up the photo that you want.
- Now you will see the photo information. Under “General” section you will have the PixelWidth and PixelHeight values. For example, if PixelWidth says 2592 and PixelHeight says 1936, your photo has a resolution of 2592x 1936 pixels.
Pixels and printing dots
Well, you already know what pixels are and what resolution in pixels your photo has.
On a screen, every pixel can have any colour. Really, every pixel is composed of three tiny dots, that you cannot see with the naked eye, which emit light with the three additive primary colours: Red, Green and Blue, and this is why it is said that screens are RGB. By varying the light intensity, every colour can be reproduced (in fact, more than the human eye can distinguish).
Printers, however, leave ink dots on the paper absorbing the light (pigments). Most printers, like the one that you have at home or at work, use three inks with the subtractive primary colours: cyan, magenta and yellow. And they use a fourth ink in black to achieve more intense blacks and to avoid wasting colour ink when only black is needed. That is the reason why they use the concept of CMYK colour (Cyan, Magenta, Yellow and blacK).
The inks in the printer are not mixed, as they are when you paint with oil or water colour. Instead, the printer prints very small dots, and every single dot can have only one of the four colours. Printing more or less dots and closely or more spread, in combination with the white of the paper, produces the optical illusion of different colours. Therefore the printer needs to print several ink dots in order to represent one single pixel.
Dots per inch resolution
When they talk about dots per inch or dpi resolution of a photo, they are talking about the physical size we want to print that photo with. That is, how many dots will be on every inch of paper. Or what is the same, the dot density on the paper.
If we say 300 dpi resolution, in a line one inch long on the paper (remember that one inch is 2.54 cm) 300 dots would be printed. Therefore, to print a picture with a size of one inch wide and one inch tall (which is a square of 2.54 x 2.54 cm) we would need 300 x 300 dots, that is, 90,000 dots.
However, if we printed the same photo with 150 dpi, that is, with lower dot density, we would get a picture on the paper with a size of 2 x 2 inches (5.08 x 5.08 cm) with those same 90.000 dots.
The more dots per inch, the more defined the picture will look, if you see it close up. But, as we explain below, if you print a large photo, for example for hanging it on the wall, you will see it from a distance and your eyes will not be able to distinguish individual dots of ink, so you will need less dots per inch.
Are you confused about inches and centimeters? Did you know that you can use Google to convert between inches and centimeters?
Let us simplify, pixels per inch and dots per inch
As you saw in a previous section, printers need several ink dots in order to represent one single pixel. But, in general, you do not need to worry about that.
When you send a photo to be printed, to a printing house or to an online photo album service, for example, you will have to take into account the dpi resolution, usually 300 dpi. This will refer really to pixels per inch. That is, how many colour dots from your photo will be printed in every inch of paper. The printer will take charge of printing many more ink dots, which are much smaller, in order to achieve the different colours.
In practice, most of the time, you can consider “dots per inch” as “pixels per inch”.
Viewing distance: the farther, the lower resolution
Pay attention to billboards, can't you distinguish the ink dots? Now look at the billboard close up and you will notice them clearly. Large format prints are for being viewed from a distance, so your eyes will not be able to distinguish individual dots and, therefore, a lower dpi resolution is needed.
But what has this got to do with your photos? Well, the larger the photo you want to print, the farther away you will be to look at it and lower the resolution needed.
So with the camera that you already have you will be able to print photos larger than you thought. Go back to the top of this article and check it with our Blurbiness® Photo Size Calculator nteractive tool.
More Megapixels does not mean more quality
Ideally, the more pixels your photo has, the higher quality you would get when printing. But the truth is that the number of pixels is not the only factor that influences the quality of a photo, and a picture with less pixels will look better when printed than a lower quality photo, even if this one has more pixels.
To understanding this better, we recommend you to read also our article The Megapixel myth: more Megapixels DOES NOT mean better quality photos.
Not all JPEGs are equal
Most likely you have your photo as a .jpg (or you have converted it to .jpg to send it to a printing house). But keep in mind that the .jpg image format allows you to adjust the compression level.
Suppose that you have a photo saved as .jpg with low compression, which means that you will have the maximum image quality that the .jpg allows, at the cost of having a bigger file size.
If that same photo, with the same number of pixels, is saved again as .jpg with higher compression, the file size will be smaller, but the image quality will be lower. So you will have the same number of pixels but with worse quality.
Why use lower quality jpg then? If you want to publish the picture on the Internet or send it by email, it will be important to have a smaller file size, and it is now when it is interesting to have a jpg with a higher level of compression.
However, if you are going to print the photo, always use a jpg with the maximum quality (lowest compression).
Most digital cameras and smartphones allow you to choose between two JPG qualities to take still pictures (look for this in your camera settings). Choose always the highest quality if you intend to print the photo.
If you know a little more about photography, you get on well with your computer and your camera allows you to take stills in RAW, then choose RAW instead of JPG. You will have more control to make adjustments to the image before converting it to JPG, instead of leaving the camera to do it all for you.
The paper quality
The quality and type of paper have a big impact on how the printed photo will look. Different kinds of paper absorb ink to a greater extent. For example, a regular sheet of paper will absorb more ink and it will be spread more, this is the reason why ink dots are not as well defined as when you print on photographic paper. Besides, the glossy paper enhances the colours.
The photo quality
The quality of the photo itself is essential too. Avoid blurred photos, ensure that they are properly focused and try to take them under proper light conditions.
If you already have a digital camera or smartphone with a reasonable quality, we encourage you to learn photography basics (with a good book, video tutorials on the internet or attending a photography workshop in your city). You will improve the quality of your photos more than by just buying a more expensive camera.
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If you have doubts or suggestions about other topics not covered in this article, feel free to leave your queries, we will write articles about the most frequently asked questions.