Help

The Document Viewer provides various means of viewing individual pages within a document, or downloading it as a whole, depending on the available classes. The meaning of the various classes is explained in more detail in How does NDAD preserve and provide documentation? Below we explain how each class is handled by the Document Viewer.

Click on a tab to jump to the relevant section.

NDAD normally stores each page of a document as a high-resolution TIFF image for preservation purposes. Because TIFFs cannot be displayed by most web browsers, the Document Viewer converts these to formats which can. And, because the stored resolution is much larger than most screen resolutions and would take a long time to download, the Document Viewer offers a choice of smaller sizes.

When you enter an IMAGE tab, you will see thumbnails (small images) of each page to help you identify pages likely to be of interest. Click on one of the thumbnails to view it at a larger size, or use the Page menu to select a specific page number. The Scale and Format controls require a little more explanation.

Scale

There are two types of scaling available, which serve different purposes.

Fixed percentage scales, ie 10%, 25%, 50%, offer the best quality because output pixels are derived from equal-sized blocks of input pixels, which tends to retain the original sharpness better. However, because the original size of the image may vary considerably, the size of image delivered to your browser may also vary and might not fit on your screen horizontally.

Fit to Width scales are designed to eliminate the need for horizontal scrolling. Choose the one which corresponds to the X resolution of your browser window; eg if you are browsing full-screen on a 1024x768 display, choose Fit to Width 1024. This will choose an appropriate percentage scaling, to the nearest 1%, so that the image is the largest that will fit within your horizontal display area, and you should only have to scroll vertically, as is the aim of most websites.

The downside of Fit to Width is that the quality of the image may be slightly lower than for the fixed scales. Some loss of sharpness may be noticeable particularly on bitonal (black and white) text images where the conversion program adds anti-aliasing to try to improve the accuracy of the rendering. In most cases this does not affect the readability of the document, but if you are experiencing excessive blurring, or if you want your image to be as true as possible to the original, use a Fixed scale instead.

Format

PNG is supported by most modern browsers. JPEG(JFIF) is offered as an alternative in case your browser has problems with PNG, but is not recommended otherwise. Because JPEG uses lossy compression, the quality is lower than PNG -- in the case of text the quality loss may be substantial, as JPEG's compression is designed for pictures rather than text.

Generally, the whole document is made available as a single text file, and this is displayed by default when you enter a document's TEXT tab. If the system is able to locate individual pages within this file, it will also offer these in the Page pulldown menu.

Remember that text files which have been created by OCR may not be accurate or complete.

The main index page of the HTML tree is displayed when you enter, and clicking any of the links within the document will normally display the appropriate page. There are some cases where this doesn't work, namely where the links are not plain HTML links -- for instance if they use Javascript.

"OTHER" files are those provided for download and viewing on your computer rather than within the Document Viewer, usually because they require additional software. Examples include PDF documents and Microsoft Excel files.

Depending on your PC's setup, clicking on the Download button may open the document directly rather than saving it. If you wish to save it to a file on your PC, this can usually be achieved by right-clicking on the Download button and selecting "Save File As", "Save Link As" or similar.