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Effects on Monitor Image Display from Downsizing


When one views on a monitor a world wide web internet full frame image intended to be printed much larger than can be displayed on the screen, the appearance of sharpness on the screen image has little to do with how sharp the print might actually appear. One often sees critiques on web forums proclaiming how sharp so and so image is. Such pronouncements are however only valid for the downsized web display image and are simply a matter of the nature of graphic image detail and sharpening at the small web image size. The below image shows the effects of downsizing for computer monitor display on the print file for image 06-Q5-3. This is one of the drum scanned 4x5 Provia 100F transparency images on my home page index.

At the top is a full view of the 11582 by 9144 pixel image as though zoomed out to 6.25% or one-sixteenth. The red square lines atop the image represents the area displayed on the next lower image crop while the small red square at its upper right is the area display by the 100% zoom bottom image. Each lower image has been zoomed out by a factor of two times which shows four times as much area and are represented by like red lines. Each of the four images below the top image are displayed as 500 by 500 pixel monitor images. The first image below the full image at top thus shows a crop 1/2.26 height times 1/2.87 width versus the full image frame. That square on the full image is a 4000x4000 pixel square that has been downsized using the bicubic algorithm by 1/8 to 500x500 pixels as though zoomed out by 1/8. The second image below shows a 1/4 zoom image, the third image below shows a 1/2 zoom image, and the fourth image shows a 100% zoom image at actual print file pixel size. All 500x500 images were conservatively resharpened.

Although the bottom image displays on a monitor at actual pixel size, it will not represent the perceived resolution looking at the 30x38 inch full Lightjet 5000 print on Fuji Crystal Archive photographic paper. That is because a typical computer monitor dot pitch is between 90 and 100 RGB phosphor dots per inch of monitor screen so that operating systems as Windows XP can only display images at something less than the phosphor dot pitch. In Windows that is a function of operator setting in the Control Panel Display function that is often either 768x1024 or 1024x1280 pixels. If the later is selected that might result in a display of these 500x500 pixel crops over a distance of about 6x6 inches of screen. However on the actual print at the full 30x38 inch size, the same section of the image will only display an approximate four times smaller 1.6 square inch area. That is because the print resolution is 304.8 pixels per inch of color information. Therefore if the same 6x6 inch square is reduced to a 1.6x1.6 inch square on a print, it would appear considerable sharper. Although the second image from the bottom that was downsized by a factor of two and zoomed in at 50% appears sharpest, if one were actually viewing on a theoretical monitor with a dot pitch as dense as the print resolution at the same sizes as the print, the bottom image would appear nearly as sharp while providing considerably more detail due to the square factor. Can you see the fly on the petals just right of center?

By comparing each image from the top down, there is a perception that each lower image seems to show considerably more fine detail. The result of each image being a square area factor showing four times as much information except for the lowest full zoom image that is a bit less due to image softening and sharpening artifacts.


downsizing
   David Senesac

   email: info@davidsenesac.com

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