Make Screen Sized Photos a Habit

If you're interested in selling photos, then you need to make a habit of creating versions with proper size and resolution for a computer screen. In a digital world, editors want to see what you have now. Don't clog someone's inbox with an image that will appear large enough to cover the state of North Dakota. Instead, have versions intended to be viewed on a monitor and send them with the explanation that high resolution files are also available for the asking. That way, the recipient can quickly review what you have and call for the big versions for which the person is willing to pay. You'll need some photo editing software, but that can be a minor expense.

Some Notes on Sizing Images: Part 5, Changing Image Size

Remember this screen from yesterday?


Now we learn how to change the image size. So long as Constrain Proportions is checked, when one things shifts, everything will. But generally you'll either want to change the size and keep the resolution the same, or change the size and resolution simultaneously. To do so, uncheck Resample Image. Now if you change the size (or pixel dimensions), now the resolution will remain the same and the image editor will make the necessary changes to the image to make everything.

So say that you have a 4x5 inch image at 300 dpi and you want the same size, but a lower resolution because you want it on the web and there's no need to use extra storage and take longer to downlond. So change the 300 dpi to 96 dpi and then click the OK button.

You can enlarge the image size or resolution, as well. Go back and recheck Resample Image. (Don't worry about the method - bicubic will do fine for now.) Now try changing the size. The resolution remains the same becuase the software is calculating what necessry changes to make.
Making an image smaller is always easier than making it larger, because in the first case you toss out informaiton, and in the latter, the software must make a calculated guess as to what additional image information it would need to fill in all those spaces that appeared when you spread the pixels out over a bigger distance. It's not perfect, but it's pretty good, and you'll have a larger image.

Some Notes on Sizing Images: Part 4, Meeting an Image Editor

Now that we know something about the resolution and image size trade-off, let's see how you'd actually change the image settings. Take a look at this screen shot from Photoshop Elements:


The top section shows you the current dimensions of the image in pixels, at you can also see that the image has 32.7 megapixels. The latter isn't necessarily the same as the file size, depending on the type of image file. A JPEG file will be compressed and, so, smaller than, say, a TIFF image file. Although you see the width and height in pixels, you can choose other forms of measurement, like inches. However, pixels is a useful choice because you can relate it to the properties of the file - X pixels across and Y pixels high.

Next section is called Document Size. This is how the image will display, and you can see both the dimensions and resolution. You can change the units here (even choose a percentage unit if you want to scale the image up or down a given amount).

In both the Document Size and Pixel Dimension sections, the a bracket with a chain connect the width and height figures. That keeps the dimensions in a constant ratio. If you wanted to change the two disproportionately (not done that often in photography, unless you're trying to distort the results), you can click on the chain and it will appear broken, telling you that the two are no longer linked.

You can also change any of the numbers and all of the others will change accordingly, so long as the Constrain Proportions box at the bottom is checked.

Tomorrow we'll actually manipulate the image size.

Some Notes on Sizing Images: Part 3, Image Size

We've looked at the image resolution. Today we start to include image size, which means the size at which the image displays. Image size is a second constraint put on an image - its display size. It's fine to know the resolution, but you also want to know how large the image will actually be. Note that you can theoretically display an image at virtually any resolution and any size - a 500 foot wide 60 dpi imge, or a 5 inch wide 300 dpi. So, when resizing an image, you will need to specify this in the image editor.

Resolution and image size are inversely related. The lower the resolution, the more you can spread out the pixels, and so the bigger the image. Similarly, the smaller the image, the more you can crank up the resolution.

This will be a trade-off: You only have so much image data and so must make due with what you have. If you have a 300 dpi image that is 4x5 inches in size, without adding to or subtracting from the image data, you can have an image double that size - 8x10 inches - but the resolution is only going to be 150 dpi, because you're spreading the dots farther apart to get them to fit in the new image display size. Similarly, you can take the 300 dpi image and squish it down to 2x2.5 images, only the new resolution will be 600 dpi. Even if you print the image to see at arm's length, you'd only need 300 dpi. In other words, you have more resolution than you really need, and that means taking up more storage for the one photo than is necessary.

What you want to do is give an image the resolution and size you really need. An application like Photoshop Elements gives you a lot of options on that front. More on that tomorrow.

Some Notes on Sizing Images: Part 2, Resolving Power

The human eye is an amazing instrument, but to distinguish between two separate points, we all need a little distance between them. But the distance is a matter of arc. If you set a compass with one leg where you are and the drawing part on one of the points, then twisted the compass so that the drawing part was on the second point, you would have just drawn an arc, or a short section of a much bigger circle. Remember that there are 360º in a circle and there are 60 minutes, or parts, to every degree.

The human eye can distinguish between two points if there is about 1.7 minutes of arc between them. However, the actual linear distance between them is the amount of arc times the distance from you to the points. The farther away the points are from you, the farther away they can be from each other and still keep the same amount of arc between them.

The idea behind images is that we don't want the eye to be able to distinguish between the points. Otherwise every picture would look like a bunch of points - like a pointillist painting by Seurat. The closer you get, the more you notice the points. But if you move away far enough, then everything blends together to look like a continuous image. So when you are resizing images, you need first to understand the resolution you want, and that depends on the medium you choose to display the image and the conditions under which an audiece will see it. (Tomorrow, something on image size.)

Some Notes on Sizing Images: Part 1, Resolution

One of the most common thing to do with photos is resize them, whether to get the ready for the web, fit them onto 4 x 6 standard prints, enlarge them, or even crop to improve the composition. And your ability to do any of these comes down to resolution and image size. Resolution refers to how many little digital dots you have in a given linear measure. For example, you might have 300 dots per inch (dpi) on a traditional print, or you might have 96 pixels per inch (ppi) for a screen display of an image. Here's an example of resolutions you'd need for some common uses:

Use	Resolution (in dpi/ppi)
Monitor viewing	96
Prints to be seen at a couple of feet	300
Prints to be seen at ten feet	60

The word resolution is clearly related to the word resolve, and that's the whole issue, as we'll see tomorrow.