How to Take Pixels Out of an Image in Photoshop CS6
When you downsample in Photoshop Creative Suite 6, you eliminate pixels and therefore delete information and detail from your image. Although there are several pitfalls of resampling up, you can sometimes damage your image by downsampling, as well.
Granted, downsampling is sometimes necessary when you’re converting high-resolution print graphics into web graphics. For example, you may be forced to take images used for a corporate brochure and repurpose them into content for the company’s website. You probably won’t notice much degradation in image quality because the images are just being viewed onscreen.
In addition, downsampling can occasionally camouflage the moiré patterns caused by scanning halftones. Keep in mind, however, that 72 ppi isn’t sufficient for printing an image.
You should never need to make an image smaller than 72 ppi.
To remove pixels from an image, follow the steps above and change the image settings accordingly.
If you have to downsample your image significantly — for example, to 25 percent of its original size — you may get better results if you do several successive 50-percent downsamples, applying an Unsharp Mask or Smart Sharpen filter on the image in between each image sizing.