How To Resize a Photo: Part 2 – Digital Photography Tip of the Week

Last week I started my discussion on how to resize an image in Photoshop Elements 5. This week I will conclude that discussion.

The difference between the Pixel Dimensions section and Document Size section of the Image Size dialog box is that changes in the Pixel Dimension section will add or remove pixels from your image and changes in the Document Size section will not. Using the same example from last week, my current image dimensions are 1200 x 1161 pixels, or 16.667 ” x 16.126″ at 72 DPI. If I wanted to print this 8 inches wide, I would first turn off the Resample Image checkbox (which tells Photoshop to add or remove pictures, and disables the Pixel Dimensions section) and then change the value in the width text box in the Document Size section to 8. When I do this, the height will automatically changed to 7.74″ and the Resolution to 150 DPI. At this point, I have not added or removed any pixels (data) from the image so the integrity of the original image remains.150 DPI is a little on the low side for printing though. To keep the size of the image the same (8 x 7.74) but print to 300 DPI, turn the Resample Checkbox back on. Changing the Resolution from 150 to 300 will now keep the document size the same, but the Pixel Dimension of your image will now be 2400 x 2322.

imagesize.gif

When resampling an image, there are 5 resampling methods you can use, Nearest Neighbour, Bilinear, Bicubic, Bicubic Smoother and Bicubic Sharper. The last three are the ones used for photographs most often. I generally only use Bicubic in my photography, though I rarely change pixel dimensions unless I am posting my image to the web. Bicubic interpolation uses adjacent pixels up, down, left and right to determine what colour pixels to add or remove as part of the image resize process. It is suggested that scaling up large amounts to use Bicubic Smoother to help eliminate some of the jaggies introduced into the upscaled image and Bicubic Sharper when scaling down to account for the loss of detail that will occur as image data is removed during downscaling.

The Scale Styles option will scale styles such as layer styles, borders and drop shadows up or down as necessary when resizing the image. I never turn this option off. When resizing for the web, simply use the Pixel Dimension section of the dialog box as computers ignore resolution and display images based upon their physical pixel dimensions.

Ultimately, it is always best to start off with the largest file size you have. I have suggested in the past that you should always shoot on the highest resolution your camera can record. Doing so will eliminate much of the need to upscale your image for a large print, while still allowing your to easily downsize your image when needed. It is better to have to downsize and throw away data than try to add data to your image when you upsize the image. As it is, my 6.1 MP digital camera can produce a 12″ x 18″ image with a resolution of 170 DPI, or an 8″ x 12″ image with a resolution of 256 DPI, both a very acceptable range for normal viewing distances of images of those sizes.

Until next time, happy shooting.

The digital photography tip of the week is written by the PCIN Assistant Editor, Chris Empey. Chris is a long time photographer and is currently the President of the Niagara Falls Camera Club. You can see more of his photography at his Photo of the Day website.
If you have a tip to send Chris, or a question about digital photography he can address in the newsletter, send it to chris@pcin.net.

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