Photograph Display Quality Testing and Analysis Page
This page displays a variety of images that have been processed to minimize the "sharpening" effect the WIX Media Server induces when presenting images to a viewer's Web Browser. This effect is most noticeable with Black and White images, and seems to be less of an issue with color images. However if you are noticing an oversharpening effect on you color images the below outlined methodology may offer some mitigation.
The images have been reduced from larger files (6016x4016 300 pixels) and (7920x1008 by 720 pixels) down to an image that measures 2100 pixels on the long side and has a pixel density of 300 pixels per inch (ppi).
For the images below, Photoshop was used to process the reduction from the original dimension down to the 2100-pixel by 300-ppi dimension. The Bicubic (smoother gradient) setting was used since the Bicubic Sharper (reduction) setting was adding to the over-sharpening effect that occurred once the images were posted to the site.
Use of Gaussian Blur to Mitigate Over Sharpening
The images were originally processed for printing on an Epson R2400 Printer. To reduce the WIX sharpening effect several tests were done using gaussian blur settings of 0.3px, 0.5px, and 1px. For Comparison, the Gallery Below also includes images that have been resized w/o applying the gaussian blur to illustrate the over-sharpening effect induced by the WIX media server.
I have purposely included very detailed images since the sharpening issue is most apparent in those kinds of images. Images with fewer edges (i.e., sky, clouds, water, smooth surfaces etc.) are less susceptible to the sharpening effect. Note the sky area in the top four images. Note also that the effect of a 1px gaussian blur on the second image in the top row is much greater that the effect it has on the second image in the second row.
When preparing your images, you will have to be the judge regarding how you prepare your images for the site. You might want to avoid the typical "last step before printing (sharpening)" that most of us do. If you have already "sharpened' your images then consider the gaussian blur approach.
Click images for larger view. Note: all images are 2100-pixels on the long side
1 Pixel Blur
0.5 Pixel Blur
0.3 Pixel Blur
Effect of Not Sharpening the Image
The above images were all shapened in Photoshop for printing and showed signs of oversharpening as a result of the WIX media server.
The following images are included to demonstrate the difference between an image that has not been sharpened for printing and one that has been sharpened but with the above described gaussian blur technique applied.
The original image demension was 6016 x 4016 pixels by 300 ppi (full frame Nikon D610). Photoshop was used to re-scale the image to 2100 pixels on the long side while maintaining the 300-ppi setting.
Take a close look at each of the images. The Unsharpened image looks best when presented by the WIX Media Server. The image that was sharpened for Printing looks over sharp when it is presented by the WIX Media Server. The three following images employ the blur technique described above. The 0.3-pixel blur looks closest to the Unsharpened Image but the 0.5-pixel blurred image also looks satisfactory.
Below the Gallery is an enlarged Screen Grab of the image that illustrates where you might want to look when examining the below images to compare the effect of over sharpening.
Click Images for larger view. All images are 2100-pixels on longest side and 300ppi.
Sharpened for Print
Sharpened 4 Print
1-pixel Gaussian Blur
Sharpened 4 Print
0.5-pixel Gaussian Blur
Sharpened 4 Print
0.3-pixel Gaussian Blur
When examining the above images check the edges of the domes where they meet the sky. In the over sharpened image you will see a halo caused by increasing the edge contrast between the lighter and darker areas. You will also see degredation in the tonal structure on the face of the large dome on the left of the image where some of the edges show a little bit of the halo effect. See image below for reference.
When examining Gallery images Look for the halo effect here.
Image Size and Resolution Study
This section illustrates how the WIX media server (along with it's sharpening effect) will display images that have been resized using different dimesions (length of image's longest side) and pixel resolutions (ppi). The image was taken with a Nikon D610 24 megapixel full-frame Camera. Original image size was 6016 x 4016 pixels at a resolution of 300-ppi when opened in Photoshop. The image was processed in Photoshop without any reduction, or cropping. The image was not "sharpened for printing", but did have clarity adjusted in Lightroom. Re-scaling the image for this study was done using Photoshop with the Bicubic (smoother gradient) setting. NOTE: Even though the images have different ppi dimensions ranging from 300-ppi to 72-ppi, the file sizes for each set of images did not change even though the ppi was changed . The different ppi settings were employed to see if they would cause any measurable degredation of image quality resulting from the resampling process occuring during resizing of the image.
Click images for larger view.
In the final analysis, it is felt that the 1400-pixel "on the long side" at 144-ppi provides the best compromise between image quality and file size while compensating for the WIX over-sharpening effect, and while maintaining reasonable page/image "loading" times. This is a specification that will be used for all images that members have submitted that "have not been processed for optimization" but are submitted with the request that the Photo Editor handle the rescaling effort. We are currently using Lightroom (with the NO sharpening setting) to rescale images.
During this process it was also determined that image quality will also be affected by the resolution and quality of the viewer's display screen and even by the different Web Browsers that are being used. While it may be obvious to some, it was rather dramatically demonstrated when viewing the images on a on MAC Retina Display, a calibrated LeCie 320 1600x1200 pixel Graphic Display driven by a PC and high-end graphics card, and a iMac 21" desktop.
We have published a new Photography Submission Guide and it is available as a pdf file that you can downloaded by clicking on the icon below:
Photo Submission Guide
Release V.02 Date: 12.24.2015