resizeThe task of resizing images in Photoshop and other editors is a bit confusing. Do you “Resample Image” and what is image dimension versus pixel dimension? To get to the Image Size dialog box open an image, and go to Image>Image Size.

As you can see in the example, the Pixel Dimension box shows the file is a 1.14MB JPEG file and how many pixels are in the image. The document size box shows you how big your image will print and at what resolution. Resolution for print is generally at the 300ppi.

As for image quality on the web, a resolution of 72ppi has been the norm, however, the web is now leaning toward 90ppi to take into consideration iDevices and other monitor sources that are offering up gorgeous images. But remember – a large image will slow down a website’s page load, which of course is taboo, and printing a large sized low res image will look totally degraded and blurry.

When it comes to using images over the internet, digital images have no absolute size or resolution.  All it has are a certain number of pixels in each dimension.   The resolution changes as the image size changes because the number of pixels that make up the image are being spread across a lesser or greater area.

For web use, the DPI is meaningless. It is only useful for a file that will be printed. For web use the important part is the pixel dimensions. HTML uses pixel dimensions to control the size of an image in a web page. The size on any particular display will vary because 72DPI is no longer the norm. Most modern displays are actually above 90DPI.

You will always have a loss of image quality when you upscale an image. The information is either there, or it is recreated by some software. I understand that the software for enlarging images offered by Alien Skin does a great job, although I have never used it.

You wouldn’t want a humongous image to have to download while someone was visiting your website.  It will take too long to download and it is just not necessary to have such a huge file.  You have complete control over all of the images you have if you understand some of these basic Photoshop concepts.

Images to a Smaller Size

When you make an image smaller, you will be losing pixels in the process.  This is when you check the “Resample Image” box.  Resampling is a process in which the number of pixels (the tiny dots that make up an electronic image) is changed to modify the overall size and resolution of an image. It reduces the number of pixels in the image, leaving as much of the image as needed to maintain high quality while removing unneeded data to help the image and your page load quickly.

Check the Bicubic Sharper, which is a high-quality method for reducing the size of images.  It is based on Bicubic interpolation but also adds some sharpening.

Resizing Images to a Little Larger

Even small enlargements require adjusting the pixel dimensions. Keep “Resample Image” box unchecked to keep the pixels the same. If you are printing an image that has been enlarged a bit, you will have to see which resolution will look best. Try 240ppi (pixel per inch), and adjust according to the rules in this post – 300ppi has the most detail for print.

You can try enlarging the image 5 percent to 10 percent at a time.  Make sure Bicubic Smoother is checked, and that Resample Image is off.  In some cases you may need to purchase software made specifically for enlarging images.  Check the reviews and try any trial versions of upsampling software before you make your purchase.

Resizing Images to Much Larger

Using the Bicubic Smoother is a high-quality method for enlarging images and is based on the Bicubic method but adds some contrast while also attempting to produce smoother results.  Make sure you you check this, and that Resample Image is off.

There are several methods for re-sizing images, and thankfully, Photoshop lets you try a variety of things within the Image>Image Size menu.

Resizing for a Specific Size

If you ever need to produce an image that has a required image size, which can include max MB size, or you want to email a large image that is for use over the internet and want to shrink it, you will need to start maneuvering the pixel dimensions. Check “Resample Image”, adjust the width or height, use the scrubby sliders if you wish. If you are using images for online use, you can easily stay under 1000 either in width or height.  Use either Bicubic Smoother or Bicubic Sharpener.

Minimum megapixels for quality prints:

Max Print Size           Minimum MP         Resolution
4 x 6″                         2 megapixels        1600 x 1200
5 x 7″                         3 megapixels        2048 x 1536
8 x1 0″                       5 megapixels        2560 x 1920
11 x 14″                     6 megapixels        2816 x 2112
16 x 20″                     8 megapixels        3264 x 2468
16 x 24″                   12 megapixels        4200×2800

Retina Display is a brand name used by Apple for liquid crystal displays which they claim have a high enough pixel density that the human eye is unable to notice pixelation at a typical viewing distance. The term is used for several Apple products, including the iPhoneiPod TouchiPad, and MacBook Pro. As the typical viewing distance would be different depending on each device’s usage, the pixels per inch claimed as retina quality can be different for the smallest devices (326, iPhone and iPod Touch): greater than the mid-sized devices (264, iPad) and greater than the larger devices (220, MacBook Pro). When an Apple product has retina display, each user interface widget is doubled in width and height to compensate for the smaller pixels. This mode is referred to as HiDPI mode by Apple.

First Retina Display: iPhone 4 326ppi Pixel

Apple has applied to register the term “Retina” as a trademark in regard to computers and mobile devices with the United States Patent and Trademark OfficeCanadian Intellectual Property Office, and in Jamaica.  On November 27, 2012 the US Patent and Trademark office approved Apple’s application and Retina® is now a registered trademark.


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