Cropping photos: how to enlarge small subjects at printable sizes
Photographing small subjects often requires cropping photos later on the computer. Our latest Photoshop tutorial shows you how to expand your smaller subjects and enlarge subjects the safe way – at printable sizes – in any version of Photoshop CS or Elements.
There are a lot of fascinating small animals and insects around – photogenic, but also tiny. Even with a macro lens, you’re unlikely to get a subject such as our spider to fill the frame, so you’ll probably want to crop your photo in the digital darkroom.
Doing this, however, means you’re discarding part of the image, which may well become a problem when you come to print.
Cropping in tight on the spider in our shot has left us with only around 900 x 750 pixels. Conventional wisdom says that for photo-realistic quality you need to print at a resolution of at least 240ppi (pixels per inch), which means our cropped image can’t be printed at bigger than about 4 x 3 inches.
Our original shot
Even if we push it and print at 150ppi, we won’t get bigger than about 5 x 4 inches without risking the image becoming grainy and blurred.
If you want to print a similarly hard-cropped photo at 10 x 8 or A4 size, what you need is some way to enlarge the cropped photo for printing that preserves its crispness and detail. You need to not just enlarge but resample.
Cropping photos correctly in any version of Photoshop CS or Elements
1 Crop to size
The Crop tool gives you the option to specify Height, Width and Resolution for your crop. If you have a size in mind, feel free to enter it; this will constrain the crop frame to the correct proportions, even if you resize it. Draw the crop frame, then drag it to reposition it as desired.
2 Don’t specify Resolution
Leave the Resolution field blank, and don’t select a preset size. Presets are based on resolution (in Photoshop, 300ppi) as well as size. Enter a value in the Resolution field, Photoshop will interpolate (add pixels) to reach that resolution, but for more control do this separately.
3 Test Image Size
After cropping, go to Image>Image Size. Ensure Resample Image is disabled, choose inches as the units from the pop-up, and type in the print Width or Height you want. If the Resolution figure is below about 180ppi, you’re spreading the image pixels too thinly for a crisp print.
4 Configure Resampling
Enable the Resample Image option, and select Bicubic in the pop-up menu. Enable Constrain Proportions, then specify a Width or Height and an adequate Resolution, and Photoshop will generate new pixels to plug the gaps.
5 Sharpen for output
The interpolated pixels are based on existing pixels – in an area of brown, for example, Photoshop will add an average brown. It can’t create new detail, so you can’t enlarge beyond about 1.5x or 2x at most and get a crisp image. You’ll also need to sharpen before printing.
Photoshop Tip: Play the percentages
You might get better results if you stick to relatively even multiples of the image size, so try selecting ‘percent’ in the units pop-up and specifying not a new Width but ‘150 percent’ or the nearest to what you want. Even if you’re using resampling, though, enlarging too much will make the image become indistinct and blurred.
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on Tuesday, December 18th, 2012 at 12:10 pm under Photoshop Tutorials, Tutorials.
Tags: macro photography, Photoshop effects, Photoshop Elements tutorials