Definition

The optimal viewing scale is determined by the highest resolution
at which ​an image is of excellent quality, and has no visible defects.

Scale affects defect visibility

​Wrong focus, graininess, processing artefacts can detract from an image's appeal. ​Viewing an image at a smaller size or scale factor, can make degradations less visible or annoying, improving the image's perceived quality.

A down-scaled version (20%) of an original photo, showing excellent quality and no visible defects. This is the optimal viewing scale if it is the largest resolution that is also of excellent quality.

A crop from the original 6000x4000 px photo (100%). The image appears to be of low quality, blurry, and grainy.

​Quality defects, reduce image clarity and fidelity

A high quality image (left) is degraded in several ways (right). The images are heavily degraded on purpose, to make the degradations obvious.
The optimal viewing scale of the distorted images is very small in this case.

Finding the ​​optimal scale

A high-resolution, but out of focus and thus low quality image is downscaled to a lower resolution (left image). At the optimal viewing scale the image shows no quality degradation, and important image details are sharp and clear (middle). Further downsizing does not help further improve the quality of the image (right).

    At the optimal viewing scale:
​

• the image is of excellent quality
• it is well focused, clear and of high fidelity
• it is not showing any noise, artefacts, or other defects
• the image is best suited to be printed or displayed
  ​e.g. wall prints, magazine cover, desktop background, etc. 

In the examples below ...

​Each row shows crops taken from the same source image. Each crop is extracted after previously downscaling the source image by a different amount. You can often notice strong degradations at the original size (left-most), whereas the lowest resolution is of excellent quality (right-most image).
The OPTIMAL SCALE is often somewhere in between.

​Note: it is best to view each image as is, do not click to enlarge.

slightly blurry

OPTIMAL

similar quality to the one on the left, but lower resolution

very blurry and grainy

still slightly out of focus

OPTIMAL

out of focus

slightly out of focus

OPTIMAL

slightly over-exposed

OPTIMAL

OPTIMAL

OPTIMAL

slightly blurry

OPTIMAL

OPTIMAL

OPTIMAL

over-sharpened

OPTIMAL

Participating in the experiment

You will annotate images using a browser-based interface, called Zovi. This allows browsing a collection of images, zooming to select the optimal scale for each, and saving the selection.

Zovi UI controls

Zoom: use the zoom slider at the top of the screen ​
Pan: click and drag the image​
Next image: press the green arrow buttons or the right arrow key.

Zovi annotation interface for selecting the optimal scale / zoom.

Steps to complete the work

1. Open Zovi in the Chrome web-browser
2. ​Select the optimal scale for each image
3. Move to the next image and repeat​
4. Submit your results at the end

2. ​Select the optimal scale

• explore the image to find any visible defects
• zoom out until the defects are no longer visible
• repeat, if necessary, until no other defects are found​

It takes about 15 seconds to find the optimal scale/zoom for each image. 
​Thank you for participating in our study!