Preparing an image crop for presentation

Sometimes less experienced photographer had a very nice image, but then when they plan to view it on screen the image could not fit the entire screen.  After cropping it become not nice anymore due to unideal composition.  Moreover sometimes improper cropping results in printed image that looks bad due to jagged lines and artefacts. 

This article will discuss cropping tips which has nothing to do with crop factor.  Crop factor is the comparative size of a full size to a camera sensor. 

Why cropping tips?  Because some less experienced photographer had a ruined image due to bad cropping.  Bad cropping ruin the compoition while composition is one of the most important aspect in photography.  A good image on 3:2 format might not look as good when cropped on 4:3 or 16:9.  This article will discuss on tips in cropping, why photographer crop an image, and how to create an image from 3:2 format camera to be crop friendly.

Warning for professionals: Excellent photographers has the necessary skill for cropping image automatically on the camera, while most less experienced ones has no such skill.  Therefore less experienced ones usually fiddle image on computer to make it fit the screen.  Photography teachers won't be happy with this tricks ^^ but they helps me a lot!

Finishing a photo session does not mean the works ends there you will need figure out where and how will you present the image, on a digital display or printed on a paper.

Preparing a crop for digital display

There are ways to display the image captured,.  On a computer, TV, mobile phone, PDA all with their own resolution and aspect ratio.  The problem arises here, most SLR's aspect ratio is 3:2.  While the two most common screen aspect ratio is the 4:3 for normal television and computer, plus 16:9 HD widescreen.  The illustration below is made using 3:2 SLR, I've put two coloured rectangles to help you understand the aspect ratio.  I give the 4:3 aspect ratio red colour and for the 16:9 I give blue.

As you can see, the blue line will cut the image's top and bottom.  The image inside the blue frame is what will you get when cropping this image at 16:9.  The red frame on the other hand will cut the image on its left and right.  Don't worry, we can move those lines more top or bottom and more left or right.

4:3 are not a problem for Olympus other 4:3 system user, but it is a problem for Canon and Nikon users, which count for more than 90% of DSLR photographers.

When to crop?

1. When the photographer find a small interest point and he or she have some limitation so that he or she can't took it at full size.  The solution: just take the image as a whole then crop it later on a computer.
2. When the photographer see a point of interest, but had no idea on how to put it on the camera.  The solution: Set the lens on wider angle, then took picture.  Finish the image editing on the computer.
3. When the photographer is in hurry, therefore he has no time to do in camera cropping.  Solution: Just use wider angle to capture the big picture, then do cropping on a computer.
4. When the photographer's lens is not long enough to properly cover the subject in filling the image.  Solution: use the maximum tele available on your lens, then do cropping on a computer

Therefore less experienced photographer needs to follow these tips to maximize their image:

1. Use the sharpest lens and camera available.  Sometimes the image is magnificently composed, therefore needing a crop size that is so small and needed to be viewed at 100 or more % on screen.  A Sharp lens will forgive you, that is because your image will stay sharp at those magnification.
2. Do not fill the whole image area with the subject.  It is always best to provide some spare unimportant area if you plan to cut it later on.  Example: when you intend to took a landscape image and then use the image on wide screen, you will need to spare few pixels on top and bottom of the image.  Those pixels will be removed in the cropping process.  Therefore, if you are planning to crop your image, always spare some pixels on the left, right top and bottom of the image.
3. Cropping into HD or other format is not a problem.  Modern DSLR has very high resolution, my EOS 400D has 10MP, while HD is only 2MP.  So 10 MP images would easily cropped into smaller size without any serious image degradation.  Illustration on 10 MP picture compared to other popular screen resolution.
   • Illustration of HD 1080i (1920 x 1080, red), 720p (1280 x 720, green), XGA (1024 x 768, blue), and SVGA (800 x 600, yellow) to the original 10 MP image of the EOS 400 D
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4. The most important thing is the image proportion and composition.  Plan your image so that you will sill had nice composition after cropping the image.  E.g., when taking a group of people picture, don't fit the people to the frame.  Since cropping into 4:3 will render some people invisible,

How about cropping for portrait?

For portrait, cropping is even more important.  Most of the time SLR user will want to crop their image to look proportionally better.  SLR's 3:2 is too thin for most occasions, then cropping to 4:3 will make the image looked proportionally better.

This strategy is not future proof however, since the screen resolution will increase and your image will looks outdated or small when high DPI digital display arrives.

Preparing a crop for print

Preparing an image for print is slightly different compared to digital viewing.  Aspect ratio is not an important issue here, since most people are fine with 4:3 or 3:2.  16:9 is too wide to be comfortably held by hand.

Is the resolution number important for image printing?  It is not!  A 100 megapixel image will looks crappy when printed at huge bill board size and viewed from few cm away.  People will see the artefacts here and there.

The more important thing is the DPI, dot per inch number.  DPI is the density of dots per pixels.  When you had higher DPI, e.g. 300 DPI image the image will look better, has less hard edges and less blurs.  On DSLR like my EOS 400 D, the DPI is only 72, quite low.  This make the image will looks crappy when printed at full size (1.371 x 0.914 m) and viewed from 25 cm away.  It is fine when viewed from 1 metre away, which is the common gallery viewing distance.

Don't worry about the low DPI count on camera, most photo editing software can up sample the image without any loss of quality.

One the DPI count is one factor to be considered when cropping an image to be viewed handheld.  That is, human eyes could feel uncomfortable staring an image with less than 300 DPI at reading distance (25 to 30 cm).  Therefore when printing small hand held article, you will need to set at higher DPI.  Human can notice hard edges and jagged lines when viewing a lower than 300 DPI image.

Up sampling from 72 DPI to 300 DPI will make the image's printing size smaller.  Therefore you if you plan to print the image on hand held size or short viewing distance should rethink when you are about to use this shot and crop strategy. 

Therefore the best and easiest way to prepare image for printing is by following this steps:

1. Up sample the image to 300 DPI.

2. Crop the image in cm or inch, but not pixels.  While human body needs absolute size in cm or pixels to comfortable hand held and see an image, pixels size are relative.  Pixel size depends on the DPI number, the higher the DPI the smaller the pixel.  An 3000 pixel image is only 10 inch wide at 300 DPI, however it is 20 inch at 150 DPI. 

3. Resize the image to the desired size, in cm or inch.

This will result in higher than or equal to 300 DPI image, which is more than human eye's capability.  Actually there are other more advanced ways to crop more accurately.  However that involves a lot of calculation which might be too complicated, but that way only improves the picture quality insignificantly.

This strategy is more future proof however, human hand's size does not change significantly over generations, therefore having an image that fit today's adult hand will also fit future's adult hand.

Final words

This article is intended only as a guide.  Follow at your own risk.  I can't be held responsible for any lost of image or quality by following my tips.

A typical computer screen has around 100-108 DPI, which is quite low.  That is why we can see the jagged when playing 3D games and on texts.