Resizing an Image
The greater majority of computer monitor screen resolutions are between 800x600 thru 1280x1024, with the majority in this range being 1024x768. Because of this it is very important that you resize images when uploading to the web or emailing pictures to your friends. How many times have you received a huge email with 1 or 2 images in it, and when you opened them up all you see is the top left of a picture with these huge scroll bars on the right and bottom of the picture??
The image below illustrates the relative difference in the size of a picture (in pixels) between a recommended web/email image size, which is 800x600 vs. a 3.2MP image (2048x1536) and a 6MP image (3000x2000). As you can see, there is a huge difference between these images. In order to allow people to see your pictures without having to resize the picture themself, or having to scroll through and imagine what the picture really looks like -- you have to resize the image.
To resize an image in Adobe Photoshop, you will need to make the following menu selection (Image - Image Size):
After making this selection, you will need to enter the size in the dialog box that appears on the screen. Before you enter the dimensions of the image that you want to resize to, there is a check box (which is checked in the image below), called 'Constrain Proportions'. This is a very important option. Keeping this checked will allow you to change only one of the dimensions, the software will determine the other dimension keeping the image properly proportioned. If you uncheck this option, the image will be stretched one way or the other. To change the image size, just enter the desired image size. In this case, changing the width to 800 pixels automatically changed the height to 569.
The other option in the resize dialog box is the 'Resample Image'. When resizing the image, you are essentially taking pixels out of the image. The software has a few different ways of doing this, these are called interpolation methods. These interpolation methods tell the software what to do to determine which pixels remain when making an image smaller and conversely, these methods determine how to create new pixels when increasing image size. The different interpolation methods available in each software program vary. In Photoshop, the methods are:
- Nearest Neighbor - fast but not precise, this is probably okay for photo sharing.
- Bilinear - Medium quality, some trade offs in speed are replaced by additional image quality.
- Bicubic - This is the slowest and most precise interpolation method.
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