By Jiawei Zhao
I apply the set of usability principles (i.e., heuristics) proposed by Nielsen and Molich in 1990  to the MacOS application Preview, that is used for viewing images, pdfs and other documents. I organize the evaluation by a set of identified tasks which cover the main features of the application. For each task, I evaluated the user interface elements to check their compliance with the selected set of heuristics to look for usability problems or drawbacks. For each problem, I give one or more suggestions to improve it.
All Defects Found
For Viewing Pictures
1. Naming of the toolbar is inappropriate
In the “Markup Toolbar”, other than the tools used to mark up, there is still a tool which is not used to add marks on the picture, that is adjusting the size (see Figure 1). Hence, naming the toolbar to “Markup toolbar” is not very reasonable. Doing so can mislead users and let them think that the tool of adjusting size is not here. But it is indeed here, which is not consistent with the user’s expectation. Therefore, this naming violates the principle “Consistency”.
|Figure 1 Inappropriate naming of the toolbar|
Suggestion: Just name the the toolbar to “toolbar” or “toolbox”, since these names are general and obvious.
2. Making a clickable thing be just a textWhen a user is adjusting the size of a picture, there is a text which shows the resulting size of the picture after adjusting. Actually, one can click on this text to switch the format of the resulting size (see Figure 2). Because it is just a text, a user can hardly realize that it can be clicked. However, it is indeed clickable, which does not comfort to the user’s expectation. Hence, making a clickable thing be just a text, which is not reasonable and violates the common sense, does no obey the principle “Consistency”.
Figure 2 Different formats of the resulting size
Suggestion: A little icon indicating the user can switch the format of the resulting size should be put next to the text.
3. The button for cropping the picture is invisible at firstAfter the user selects one area on the picture, there will appear a button named “crop” in toolbar. Then the user can click on the “crop” button to clip the picture (see Figure 3). If the user does not select an area, the “crop” button in the toolbar is invisible, which can mislead users and let them think the function of clipping is not here. So, this violates the principle “Consistency”.
Figure 3 “Crop” button is invisible at the beginning
Suggestion: Disable the “crop” button when one does not select an area on the picture rather than making it invisible.
For Viewing PDF files
1. Search in the text
When finishing searching, there is not a note or a reminder of which page the user was in before searching. If the user is reading a very long e-book and wants to continue reading after searching, he will have to find the page he was reading before searching by himself. This violates the principle “Shortcuts” and this is a serious usability problem since it makes the reading very inefficient.
Suggestion: Add a shortcut or a note so that the user can directly jump to the page or get to know which page he was in.
2. Highlighting and unhighlighting a text use the same operations
There are no usability problems with highlighting. However, for unhighlighting, there is a usability issue. More exactly, when the user wants to unhighlight a text, one has to select the same color and brush the text he wants to unhighlight. So the operations of highlighting and unhighlighting is same, which violates the principle “Consistency”, since the user can hardly know using the operations of highlighting to perform unhighlighting.
Suggestion: Add an option of unhighlighting is reasonable and desirable.
3. The contents of the added bookmarks cannot be edited
Although a user can add bookmarks, the contents of the bookmarks cannot be edited. Sometimes the contents of the bookmarks are unmeaning and even unreadable (see Figure 4), if the user cannot edit it and add meaningful contents, one can hardly know the meanings of the bookmarks. Not allowing users to edit the contents of the bookmarks violate the principle “Speak user’s language” since users not only cannot understand the original contents of the bookmarks but also cannot edit the contents and add meaningful things.
Figure 4 Unreadable and unmeaning contents of bookmarks
Suggestion: Allow users to edit contents of the bookmarks.
4. The button for inserting a new page is unobvious
In order to insert a new page, one can first click on the toolbar icon and then click the “+” button on the far left bottom corner of the whole window (see Figure 5). This inserting page (“+”) button is far away from other tools in the toolbar, hence users will hardly notice it. And this violates the principle “Consistency”, since the same kind of things should be located at the same location.
Figure 5 Inserting a page
Suggestion: Put the inserting page button (“+”) on the toolbar.
1. Cannot undo the change of the window background colorIn the preference setting, one can change the background color of the window (see Figure 6). However, the problem here is the user cannot undo the changes. Maybe after trying several colors, the user realizes that the original color is the best, but when he tries undoing by press “Command + Z”, he founds it does not work. Hence, not providing “undo” violates the principle “Clearly marked exits”.
Figure 6 Modifying background color
Suggestion: Allow the user to undo the changes of the window background color.
After the heuristic evaluation on the Mac’s built-in picture and PDF viewer Preview, I found some usability problems. Most of them are associated with the principle “Consistency” owing to the inconsistency with other applications or the user’s expectation. Other usability issues are related to the principle “Shortcuts”, “Speak the user’s language” and “Clearly marked exits”. The things I feel uncomfortable about while I am using Preview are just the usability problems identified through the evaluation.
 Nielsen, J., and Molich, R. (1990). Heuristic evaluation of user interfaces, Proc. ACM CHI'90 Conf. (Seattle, WA, 1-5 April), 249-256.