Spring 2012

Spring 2012
by ani

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I am receiving images from clients at 300ppi that need to appear on ultra-HD screens. These images are the wrong dimensions (too small). I'm wondering if i can scale them up somehow to (without reducing image quality) by increasing dimension but reducing ppi. Any body have experience with ultra-hd images?

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"Ultra HD" just means 8 megapixel (for 4K), and is usually much less than 300dpi in actual practice. 300dpi doesn't mean much for files not displayed anywhere, though. Can you clarify the actual resolution of the images you are talking about? – mattdm Feb 14 '14 at 3:16
possible duplicate of How can I upscale a low-res image to make it appear higher-res? – mattdm Feb 14 '14 at 3:17
While this is close to the upscale question, I think the fact that it needs to match a native screen resolution puts further constraints on the problem that make it unique. – AJ Henderson Feb 14 '14 at 14:57

The DPI is meaningless until it is something is rendered at a specific size. In your case, the resolution is determined by the Ultra-HD display and all you need is something with at least 3920 pixels wide and 2160 pixels tall.

If you have more pixels in both dimensions, then you are good and there is nothing to do. If you do not even have that number, then you need to scale up. Most software like Photoshop can do that and you can use something like Bicubic Sharper option in the resize dialog to get a nice resize. It don't work miracles and you only need to size it to the dimensions required, not more. Otherwise it will get down-scaled on the display.

Most digital cameras since the last 5 years offer more resolution than Ultra-HD. It may seem high but that is because video requires a lot more bandwidth. Any 12 MP camera will more than cover the resolution you need in both dimensions.

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Ultra HD is only around 8 megapixels or less. The PPI the screen is capable of displaying is relatively low. The size you can get away with depends on the distance people will be from the screen. You can scale up the resolution without too much quality loss though you won't gain any either. I would recommend scaling it to the native resolution of the display. The inch and ppi measurements do not matter, only the pixel count.

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Phrasing it slightly blunty, no you can not scale images up without reducing quality in any way.

You need data to fill in for the "new pixels" and seeing there is only so much data in the image, some form of algorithm needs to make educated guesses at what should be in those pixels.

I believe, it's more a question of whether or not the quality losses are acceptable, which depends on the source size (as others have asked as well) as well as the nature of the picture itself. Some lend themselves better to upscaling than others, which in turn is influenced by the algorithm used to scale the image. For that, the other answers provide good information.

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