Cropping and Sizing in Photoshop

If you’re a photographer from the days of film, you will have to finally accept the inevitable: Digital photography is taking over! You will have to undertake further training in the digital darkroom! Common tasks you will encounter in digital photography are cropping, sizing and resolution of the final digital image.

Traditionally all output was in the form of prints, printed media or projection. There was no need to consider aspect ratios and resolutions. Film came in known aspect ratios as did prints. 35mm film suited the “A” scale printing industry. There was minimal cropping in matching the aspect ratio of 35mm film to say an A4 print. Many magazines, some in the USA, were designed around the A4 scale.

With non-digital photography all you had to do was scale the image to fit the paper on the enlarger during printing. Now you have to consider your output media. Digital camera sensors come in various aspect ratios such as 1:1 3:2, 4:3, 16:9 (APS-H) and others. Electronic output media comes in the traditional 4:3 aspect ratio of squarish monitor screens and old TVs and 16:9 ratios (wide-screen) as used by many laptop PCs and modern digital HDTVs.

Print media also has a range of aspect ratios different again. It seems there was little co-operation between standards used in cinema, TV, printing and camera manufacturing. The result is we compensate for the differences through resizing and cropping in post production. The biggest reason for this mismatch in standards comes down to economics. You could think of it as each device has its’ financial sweet spot that determines its’ size and aspect ratio in manufacture.

Confused yet? Well there is one consolation. Most electronic media will automatically re-scale your images to fit the screen and as long as the aspect ratios are close, not too much is chopped off, or not too much masking around the edges will appear where the screen and picture are not the same shapes. To get a full screen without cutting out any of the image, the image must be of the same aspect ratio as the screen. This becomes a challenge when the image is going to be viewed on different shaped screens, or you do not know what shape screen your images will be viewed on—4:3 squarish, or 16:9 wide shape!

So far we have only talked about aspect ratio. A property that didn’t exist in film is “resolution”. A fine resolution is many dots packed so close together you can’t see them—the image looks solid! For digital printing, 300 dots per inch is the chosen standard. A square inch will be 300 x 300 dots (90,000 in all). If your print measured 3 x 5 inches that would equate to 15 inches each of 90,000 dots. 90,000 x 15 = 1.35 million dots. You could also calculate that by (3 x 300) x (5 x 300) dots in total, or 900 x 1500 dots for print.

While we talk about dots in the printing industry, we talk about pixels in the electronic media industry. For ease of understanding at this level, consider a dot and a pixel as the same thing. So a printed picture containing 1.35 million dots could have come directly from a 1.35 mega-pixel camera without any editing.

An A3 magazine centrefold measures 16.5 inches x 11.75 inches. The closest monitor size to that would be a 22 inch wide-screen monitor. Monitors are members of the electronic media group, while magazines belong to the printed media group. Printed media requires images to be of high-resolution—that is at least 300 dpi of resolution. Electronic media only displays in low resolution by comparison—72 ppi (remember to consider dots and pixels as the same at this level of understanding). Even if you opened a 300 ppi image file, the monitor would ignore most of the pixels as it can only display at 72 ppi, yet it looks quite clear, detailed and sharp at normal viewing distance. On the other hand if you print out a 72 ppi resolution file you are going to get a bit of a fuzzy print. Fine detail will be lost to smudge, colours will be muddy, course and pixelated and nothing will be very sharp.

So for the printing industry that desires digital images to be of 300 dpi (dots per inch) an A3 sized magazine centrefold would need an image with a resolution of around 16″ @ 300 dpi x 12″ @ 300 dpi, or 4800 pixels x 3600 pixels—a total of 17.28 MP (mega pixels) approximately. You need good gear to met this standard. However, the accepted resolution for a computer screen or digital HDTV is only around 72 – 96 ppi. In fact 72 seems to be the adopted standard now. So a 16″ x 12″ image on a TV screen would only need 16 @ 72 ppi x 12 @ 72 ppi, or 1152 px x 864 px. That is a total of 1 MP (995328 p). Even a cell-phone camera can produce that resolution! However as the HDTV is unlikely to be A3 size, the electronics in the HDTV will adjust the size to fit the screen. After all when it comes to HDTV, how many different sized TVs are there? They just enlarge the image electronically to fill the different sized screens at the expense of resolution. You really only notice this when you move up close to the screen. Lucky we tend to move back further as the screen size increases, not closer!

Electronic file size (not image size here) is influenced by the image resolution. Obviously lots more pixels per image result in larger sized files and that determines how many images we can store in memory and how long it takes to create, load, or send and open these files to view the image they carry electronically. That is one reason not to provide high-resolution images for computer viewing even though the computer will automatically size them to fit the screen.

So there are now two media forms photographers have to consider and they are miles apart–print and electronic. One requires expensive top end equipment (print media) the other doesn’t (electronic media).

If you are trying to cover both markets, you are going to need good gear and a digital dark room (a computer with good image editing software) to down scale images intended for electronic media. You will need to be able to crop images to the various aspect ratios as well as resetting the resolution and thus the overall size at the required resolution.

Tips on cropping and resizing at required resolutions using Adobe Photoshop software.

While there are many programs in which this can be done, the industry has adopted Adobe Photoshop as the industry standard. At the time of writing this article, Photoshop CS5 was the latest version available. Although this article was based on CS3, this area of production applies to all CS versions, however later versions may have added functionality to these tools not covered here.

There are two tools used in cropping and sizing. The first is cropping. Instead of using the cropping tool here, use the rectangular marquee selection tool. The rectangular marquee selection tool can allow you to set the aspect ratio of the selection/crop to match your monitor, TV, or print ratio shape—square (4:3), wide (16:9), APS-C (3:2), A4 (7:5) etc. Unfortunately for best results you need to crop your images in the same ratio as the monitor you are intending to view them on. If you don’t know this, then the default standard crop is 4:3. That is the ratio of horizontal and vertical measurements of the old square—pre-wide-screen TVs and monitors, and the standard size of many digital compact camera sensors. However the newer wide-screen TVs and monitors have a horizontal/vertical aspect ration of 16:9. Now to be difficult, many of the APS-C cropped sensors used in DSLR cameras are neither of these! They have a ratio of 3:2.

If your photos are intended to be viewed on a modern wide-screen TV/monitor and you want them to fill the screen without any side being chopped off, or an automatic black mask being used to fill in where the image fails to reach the edges on your TV/monitor, then you will need to crop them to the 16:9 ratio in Photoshop. In other words you will determine what to cut out from the original image during post-production to get it to the 16:9 ratio for these TVs and monitors. The same goes for cropping APS-C 3:2 ratio images from most DSLR cameras to fit the older squarish TVs/monitors, only instead of choosing a 16:9 ratio, choose a 4:3 ratio. Now to make things worse, if you decide to print any of your images, the ratios are going to be different again. A4 has a ratio of 7:5. What you could do is crop your original image to the desired ratio and save it as a copy of your original image. One for printing and one of TV viewing! This would be the very final stage of post-production after all other editing is done except sizing.

In Adobe Photoshop CS3 the rectangular Marquee tool is best for cropping here because it offers you options of selecting to a predetermined size, or ratio, in addition to freestyle (options the dedicated cropping tool doesn’t provide in Adobe Photoshop CS3). You can set the Marquee selection tool in Photoshop to “Ratio” from the rectangular Marquee (top) tool bar when the rectangular Marquee selection tool is chosen and enter your parameters. If you wish to crop an image to fit a HDTV, or a laptop 16:9 ratio screen, you enter 16 and 9 respectively as the parameters in the ratio parameter boxes. You then drag the Marquee selection tool over your image to where you want it and crop it there by selecting Crop from the image menu on the main menu bar. Now your image is in the 16:9 aspect ratio. For an “A scale” print your ratio would be 7 and 5 in each parameter field of the ratio tool. The tool provides a button to change from horizontal (landscape) to vertical (portrait) without the need to re-enter the ratio parameters each time. Of course you have lost what remained outside the selection, so make sure you are working on a copy of the original image file if you intend saving the result.

At this point you have only set the aspect ratio to a particular output shape, at any size. Now you need to work on the size of your image output. The easiest way to size your final image after it has been cropped to your desired ratio, is to enter the desired pixel sizes into the sizing tools parameter fields. You need to know what these pixel sizes are. Here are the important ones:

  • For the standard 4:3 ratio TV/monitors (the squarish shape) enter 1024 x 768 pixels. In the vertical or portrait image orientation just enter 768 as the height and accept what the programs adds as the width.
  • For a 19 inch wide-screen monitor of 1440 x 900 pixels, use that as your parameters in the Photoshop resizing tool. In the vertical or portrait image orientation just enter 900 as the height and accept what the programs adds as the width.
  • For a 16:9 aspect ratio modern wide HDTV or most notebook monitors enter 1920 x 1080 pixels, or find out the pixel size of your notebook screen. In the vertical or portrait image orientation just enter 1080, or your notebook vertical or height pixel size as the height and accept what the programs adds as the width.
  • For a 5″ x 3″ print enter 1500 x 900 pixels into your resizing tool
  • For a 6″ x 4″ print enter 1800 x 1200 pixels into your resizing tool
  • For A5 prints (8.25″ x 5.8″) enter 2480 x 1754 pixels into your resizing tool
  • For A4 prints (11.75″ x 8.25″) enter 3508 x 2480 pixels into your resizing tool
  • For A3 prints (16.5 x 11.75″) enter 4960 x 3508 pixels into your resizing tool

So how do you work this out? For prints just multiply the size in inches of each edge by 300. For electronic media do the same but multiply it by 72 instead of 300 for Mac’s and HDTVs and 96 instead of 300 for PCs. With monitors and TVs you need to measure the real width, or height—don’t use the given size, it is the diagonal size and of no use here. For instance, a 24 inch monitor is neither 24″ wide or high. The 24 is the diagonal measurement. You will have to literally measure the width and height yourself.

Using this method you don’t have to be burdened with resolutions.

Researched and written by Gavin Lardner ©


3 responses to “Cropping and Sizing in Photoshop

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