Enlarging parts of photographs - Resolution Demonstration

Images of moderate quality are used on the Library’s web site to speed their delivery. When you purchase a print or digital image file, it will be made from a separate high resolution archive file stored off-line.

Here are instructions for having part of a photograph enlarged, and a demonstration of the differences in the image quality between our on-line and archival image files.

Enlarging part of a photograph

We can print high resolution details from any image. To order enlargements of a specific part of an image, draw crop marks on a printout of the photograph around the part you want to have enlarged, similar to what is shown above. It's best to make the marks in red, so they are unmistakable.

A list of the sizes we print is on our price list. If you are concerned about your cropped enlargements conforming to these dimensions, be sure the proportions are the same. Our proportional calculator is useful for predicting enlargement dimensions or for matching an enlargement to a particular frame. Contact us if you have other questions.

Please note that enlargements of sections of a photograph will vary in detail, depending on the resolution of the original image, which is illustrated below.

Resolution demonstration

The original glass negative for the image in our demonstration below was of high clarity, so detailed enlargements are possible. A less focused original will yield an enlargement with less detail, like the one shown above.

Thumbnail version of photograph. [Call number C-242].

A mouse click on the thumbnail will open a larger version of the photograph showing more detail [example below]. This preview image is designed for reference, but does not lend itself to enlargement or high quality printing. This is illustrated with enlargements of the contents of the red square. [Scroll down].

This is the quality of the detail found in the Web site preview image when enlarged 8 times.	This is the quality of the same detail found in the off-line, high resolution archival image file from which prints are made. It is often possible to produce mural size prints from our archive files.

Remember that ultimate image and reproduction quality is determined by the condition of the original photograph from which it is made. Out-of-focus originals result in out-of-focus copies.

Digital image specifications

Four digital image files are created for each photograph.

Thumbnail files

The first small image you see after a search is called a thumbnail file. It is 160 pixels long on its long dimension and is represented by either 256 shades of gray or 16.7 million colors. This file is compressed and stored in JPEG format.

Preview files

The second image you see after clicking on a thumbnail image is called the preview file. It is 640 pixels long on its long dimension and is represented by either 256 shades of gray or 16.7 million colors. The file is compressed by a factor of 12 and is stored in JPEG format.

Display files

These files are used within the Library network but are not available to the public through the Internet. A file is 4000 pixels long on its long dimension and is represented by either 256 shades of gray or 16.7 million colors. The file is compressed by a factor of 12 and is stored in JPEG format.

Archive files

An additional image file is stored off-line on CD-ROM. This master file is created at the time the photographs are digitized. It has a minimum of 4000 pixels along its long dimension and is represented by either 256 shades of gray or 16.7 million colors. Archive files are stored uncompressed in a TIFF format on CD-ROM's. A CD-ROM will hold between 50 and 100 Archive files. The Thumbnail, Preview and Display files are derived from the Archive files. Archive files are used to make the high resolution digital prints. High resolution versions of every image in the database are available on special monitors with zooming capabilities, at the Western History Department, on the fifth floor of The Denver Public Library. We are working towards providing this feature on the Internet.