CDL Guidelines for Digital Images

Chapter 3. Requirements

Table of Contents

3.1. Number of Images
3.2. File Formats and Compression
3.3. Watermarking
3.4. Digital Cameras
3.5. Guidelines for Derivative Files
3.6. Guidelines for Digital Master Files
3.6.1. Textual Documents, Graphic Illustrations/Artwork, Maps, and Plans
3.6.2. Photographs: Transmissive Originals (Film, Slides, and Negatives)
3.6.3. Photographs: Reflective Originals (Prints)
3.6.4. Aerials: Transmissive Originals (Film, Slides, and Negatives)
3.6.5. Aerials: Reflective Originals
3.6.6. Objects and Artifacts

3.1. Number of Images

Producers are strongly encouraged to submit at least one copy of a digital master file for each digital object. Producers must submit, at minimum, at least two derivative file types for each digital object:

An access image (a service or reference image for more detailed viewing).
A thumbnail image (for the fastest access during the search, browse, and retrieval process).

3.2. File Formats and Compression

The following image formats are currently supported by the CDL for the Enhanced Service Level. See Table 3.5 and Table 3.6 for specific image format requirements.

TIFF ITU-T.6: A 24-bit storage format commonly used by Adobe PhotoShop and other bitmap editors, this TIFF format may be used to store color images. This format is also suited for bitonal text documents; it provides a high level of detail (up to 600 dpi, or 4,800 x 6,600 pixels for a letter-sized page). TIFF ITU-T.6 format should be used for archival files. With lossless compression, the data that results from compressing and then uncompressing the image is exactly the same as the original, uncompressed file. CCITT Group 4 compression is lossless and, therefore, permissible for masters and derivatives. While compression is allowed for archival files, it is discouraged, as it adds complexity to the format migration issues of long-term preservation. When compression is used, it must be lossless and not proprietary.
JFIF (JPEG File Interchange Format): A specific implementation of the Joint Photographic Experts Group compression format (JPEG), commonly used by bitmap editing programs, viewers, and web browsers. JPEG is a 24-bit, lossy (some information lost) compression format that is well-suited for screen and print presentation. JPEG is supported by all major computer platforms and by Internet web browsers. With lossy compression, the picture quality of the compressed file is reduced when compared to the original file, and can not be restored, except by going back to the original. The advantage is that the file sizes are much smaller, and image quality is acceptable in most cases. It is not acceptable as an archival file format.
GIF: An 8-bit, lossless compression format that is well-suited for low resolution screen display of images. GIF is often used for image thumbnails and screen versions of text documents, and is supported by all major computer platforms and Internet browsers.

3.3. Watermarking

Watermarking technology of any kind should not be used on digital master files. Visible watermarks should not be used for derivative access image files, as they can lessen the legibility, quality, interpretability, and integrity of the image. The use of electronic watermarks (or "invisible" watermarks) is suggested as an alternative to visible watermarks. In general, other methods for attaching rights information to derivative access images (such as through rights management administrative metadata) is encouraged.

For a summary of the visible and electronic watermarking technology, see the Western States Digital Imaging Best Practices (pp. 24-).

3.4. Digital Cameras

Use of cameras to capture digital files should comply with the NARA guidelines.

3.5. Guidelines for Derivative Files

Table 3.5

Access Image

File format:

JPEG (medium to high quality compression, sRGB profile for color and Gamma 2.2 for grayscale).

Pixel array:

800-3000 pixels across the long dimension.

Resolution and bit depth:

8-bit grayscale, 24-bit color: 72-200 PPI.

Thumbnail Image

File format:

GIF (adaptive/perceptual palette, diffusion/noise dither).

Pixel array:

Image should fit within a boundary of 150-200 pixels across each dimension (200 pixels preferred).

Resolution and bit depth:

4-bit grayscale, 8-bit color: 72 PPI.

3.6. Guidelines for Digital Master Files

All digital master files should be in the following format, with associated technical metadata in the header file:

File format:

TIFF

Technical metadata:

Color and grayscale TIFF files should have ICC color profiles embedded in the file header, to indicate how the color and tonal values in the file are to be interpreted. Technical details for embedding ICC profiles in TIFF files can be found in the International Color Consortium's (ICC) Specification ICC.1:2004-10 (Profile version 4.2.0.0) (see p. 69).

TIFF files without embedded profiles will be assumed to be in sRGB color space if color, and Gray Gamma 2.2 colorspace if monochrome. More information about ICC color profiles can be found the ICC homepage. The Adobe Photoshop software (and associated literature) also includes considerable information about creating, embedding, and using color profiles.

Refer to the tables below for pixel array, resolution, and bit depth specifications, based on the features of the original object being digitized.

Table 3.6.1

Features of Original Object	Digital Master File
Textual Documents, Graphic Illustrations/Artwork, Maps, and Plans
Features of Original Object	Digital Master File
Clean, high-contrast documents with printed type (e.g. laser printed or typeset)	Pixel array: 6000 pixels across the long dimension for 1-bit bitonal mode. 4000 pixels across long dimension for 8-grayscale. Resolution and bit depth: 1-bit bitonal mode or 8-bit grayscale: adjust the scan resolution to produce a Quality Index (QI) measurement of 8 for the smallest significant character. For more information about QI, see the NARA guidelines. -or- 1-bit bitonal mode: 600 PPI for documents with smallest significant character of 1.0 mm or larger. The 600 PPI 1-bit files can be produced via scanning or created/derived from 400 PPI, 8-bit grayscale images. -or- 8-bit grayscale mode: 400 PPI for documents with the smallest significant character of 1.0 mm or larger.
Documents with poor legibility or diffuse characters (e.g. carbon copies, Thermofax/Verifax), handwritten annotations or other markings, low inherent contrast, staining, fading, halftone illustrations, or photographs	Pixel array: 4000 pixels across long dimension. Resolution and bit depth: 8-bit grayscale mode: adjust the scan resolution to produce a Quality Index (QI) measurement of 8 for the smallest significant character. For more information about QI, see the NARA guidelines. -or- 8-bit grayscale mode: 400 PPI for documents with smallest significant character of 1.0 mm or larger.
Documents as described for grayscale scanning and/or where color is important to the interpretation of the information or content, or desire to produce the most accurate representation	Pixel array: 4000 pixels across long dimension. Resolution and bit depth: 24-bit color mode - adjust the scan resolution to produce a Quality Index (QI) measurement of 8 for the smallest significant character. For more information about QI, see the NARA guidelines. -or- 24-bit RGB mode - 400 PPI for documents with smallest significant character of 1.0 mm or larger.

Table 3.6.2

Photographs: Transmissive Originals (Film, Slides, and Negatives)
Features of Original Object	Digital Master File
Format range: 35 mm and medium format, up to 4x5 in. Size range: Smaller than 20 in. square	Pixel array: 4000 pixels across long dimension of image area, excluding mounts and borders. Resolution: Adjust the scan resolution to meet pixel array specifications, based on the format of the original object - approximately 2800 PPI for 35mm originals and ranging down to approximately 800 PPI for originals approaching 4x5 in. Bit depth: 8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file . -or- 24-bit RGB mode for color and monochrome (e.g. collodion wet-plate negative, pyro developed negatives, stained negatives, etc.), can be produced from a 48-bit RGB file.
Format range: Equal to or larger than 4x5 in. and up to 8x10 in. Size range: Equal to or larger than 20 in. square and up to 80 in. square	Pixel array: 6000 pixels across long dimension of image area, excluding mounts and borders. Resolution: Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 1200 PPI for 4x5 in. originals and ranging down to approximately 600 PPI for 8x10 in. originals. Bit depth: 8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file. -or- 24-bit RGB mode for color and monochrome (e.g. collodion wet-plate negative, pyro developed negatives, stained negatives, etc.), can be produced from a 48-bit RGB file.
Format range: Equal to or larger than 8x10 in. Size range: Equal to or larger than 80 in. square	Pixel array: 8000 pixels across long dimension of image area, excluding mounts and borders. Resolution: Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 800 PPI for originals approximately 8x10 in. and ranging down to the appropriate resolution to produce the desired size file from larger originals. Bit depth: 8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file. -or- 24-bit RGB mode for color and monochrome (e.g. collodion wet-plate negative, pyro developed negatives, stained negatives, etc.), can be produced from a 48-bit RGB file.

Photographs: Transmissive Originals (Film, Slides, and Negatives)

Features of Original Object

Digital Master File

Format range:

35 mm and medium format, up to 4x5 in.

Size range:

Smaller than 20 in. square

Pixel array:

4000 pixels across long dimension of image area, excluding mounts and borders.

Resolution:

Adjust the scan resolution to meet pixel array specifications, based on the format of the original object - approximately 2800 PPI for 35mm originals and ranging down to approximately 800 PPI for originals approaching 4x5 in.

Bit depth:

8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file

-or-

24-bit RGB mode for color and monochrome (e.g. collodion wet-plate negative, pyro developed negatives, stained negatives, etc.), can be produced from a 48-bit RGB file.

Format range:

Equal to or larger than 4x5 in. and up to 8x10 in.

Size range:

Equal to or larger than 20 in. square and up to 80 in. square

Pixel array:

6000 pixels across long dimension of image area, excluding mounts and borders.

Resolution:

Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 1200 PPI for 4x5 in. originals and ranging down to approximately 600 PPI for 8x10 in. originals.

Bit depth:

8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file.
-or-
24-bit RGB mode for color and monochrome (e.g. collodion wet-plate negative, pyro developed negatives, stained negatives, etc.), can be produced from a 48-bit RGB file.

Format range:

Equal to or larger than 8x10 in.

Size range:

Equal to or larger than 80 in. square

Pixel array:

8000 pixels across long dimension of image area, excluding mounts and borders.

Resolution:

Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 800 PPI for originals approximately 8x10 in. and ranging down to the appropriate resolution to produce the desired size file from larger originals.

Bit depth:

8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file.
-or-
24-bit RGB mode for color and monochrome (e.g. collodion wet-plate negative, pyro developed negatives, stained negatives, etc.), can be produced from a 48-bit RGB file.

Duplicate negatives and copy negatives can introduce problems in recommending scanning specifications, particularly if there is no indication of the size of the source object that was photographed.

For copy negatives or transparencies of prints, use the specifications for that print size. For duplicates (negatives, slides, transparencies), match the size of the original object used to derive the duplicate. However, if the original size is not known, follow these recommendations:

For a copy negative or transparency, scan at a resolution to achieve 4000 pixels across the long dimension.
For duplicates, follow the scanning recommendations for the size that matches the actual physical dimensions of the duplicate.

For scanning negatives with multiple images on a single negative, see the section on scanning stereographs below.

Any reduction or enlargement in size must also be taken into account, if possible. If a ruler has been included in the scan, use it to verify that the image has not been reduced or enlarged before calculating appropriate resolution.

Often photographic negatives are the most difficult originals to scan. Unlike scanning positives, reflection prints, and transparencies or slides, there are no reference images to which to compare scans. Scanning negatives is very much like printing in the darkroom — it is up to the photographer/technician to adjust brightness and contrast to get a good image. Also, most scanners are not as well calibrated for scanning negatives compared to scanning positives.

To minimize the loss of detail, it is often necessary to scan negatives as positives (the image on screen is negative), invert the images in Photoshop, and then adjust the images.

If black-and-white negatives are stained or discolored, we recommend making color RGB scans of the negatives and using the channel that minimizes the appearance of the staining/discoloration when viewed as a positive. The image can then be converted to a grayscale image.

Table 3.6.3

Photographs: Reflective Originals (Prints)
Features of Original Object	Digital Master File
Format range: 8x10 in. or smaller Size range: Smaller than or equal to 80 in. square	Pixel array: 4000 pixels across long dimension of image area, excluding mounts and borders. Resolution: Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 400 PPI for 8x10 in. originals and ranging up to the appropriate resolution to produce the desired size file from smaller originals, approximately 570 PPI for 5x7 in. and 800 PPI for 4x5 in. or 3.5x5 in. originals. Bit depth: 8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file . -or- 24-bit RGB mode for color and monochrome (e.g. albumen prints or other historic print processes), can be produced from a 48-bit RGB file.
Format range: Equal to or larger than 8x10 in. and up to 11x14 in. Size range: Equal to or larger than 80 in. square and up to 154 in. square	Pixel array: 6000 pixels across long dimension of image area, excluding mounts and borders. Resolution: Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 600 PPI for originals approximately 8x10 in. and ranging down to approximately 430 PPI for 11x14 in. originals. Bit depth: 8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file . -or- 24-bit RGB mode for color and monochrome (e.g. albumen prints or other historic print processes), can be produced from a 48-bit RGB file.
Format range: Equal to or larger than 11x14 in. Size range: Equal to or larger than 154 in. square	Pixel array: 8000 pixels across long dimension of image area, excluding mounts and borders. Resolution: Adjust the scan resolution to meet pixel array specifications, based on the format of the original object– approximately 570 PPI for originals approximately 11x14 in. and ranging down to the appropriate resolution to produce the desired size file from larger originals. Bit depth: 8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file . -or- 24-bit RGB mode for color and monochrome (e.g. albumen prints or other historic print processes), can be produced from a 48-bit RGB file.

Photographs: Reflective Originals (Prints)

Features of Original Object

Digital Master File

Format range:

8x10 in. or smaller

Size range:

Smaller than or equal to 80 in. square

Pixel array:

4000 pixels across long dimension of image area, excluding mounts and borders.

Resolution:

Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 400 PPI for 8x10 in. originals and ranging up to the appropriate resolution to produce the desired size file from smaller originals, approximately 570 PPI for 5x7 in. and 800 PPI for 4x5 in. or 3.5x5 in. originals.

Bit depth:

8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file

-or-

24-bit RGB mode for color and monochrome (e.g. albumen prints or other historic print processes), can be produced from a 48-bit RGB file.

Format range:

Equal to or larger than 8x10 in. and up to 11x14 in.

Size range:

Equal to or larger than 80 in. square and up to 154 in. square

Pixel array:

6000 pixels across long dimension of image area, excluding mounts and borders.

Resolution:

Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 600 PPI for originals approximately 8x10 in. and ranging down to approximately 430 PPI for 11x14 in. originals.

Bit depth:

8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file

-or-

24-bit RGB mode for color and monochrome (e.g. albumen prints or other historic print processes), can be produced from a 48-bit RGB file.

Format range:

Equal to or larger than 11x14 in.

Size range:

Equal to or larger than 154 in. square

Pixel array:

8000 pixels across long dimension of image area, excluding mounts and borders.

Resolution:

Adjust the scan resolution to meet pixel array specifications, based on the format of the original object– approximately 570 PPI for originals approximately 11x14 in. and ranging down to the appropriate resolution to produce the desired size file from larger originals.

Bit depth:

8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file

-or-

24-bit RGB mode for color and monochrome (e.g. albumen prints or other historic print processes), can be produced from a 48-bit RGB file.

For stereograph images and other multiple image prints, modified recommended scanning specifications are to scan to original size (length of both photos and mount) and add 2,000 pixels to the long dimension, in the event that only one of the photographs is requested for high-quality reproduction. For example, if the stereograph is 8 in. on the long dimension, a resolution of 500 ppi would be required to achieve 4,000 pixels across the long dimension for that size format. In this case, adding 2,000 pixels to the long dimension would require that the stereograph be scanned at 750 ppi to achieve the desired 6,000 pixels across the long dimension.

For photographic prints, size measurements for determining appropriate resolution are based on the size of the image area only, excluding any borders, frames, or mounts. However, in order to show that the entire record has been captured, it is good practice to capture the border area in the master scan file. In cases where a small image is mounted on a large board (particularly where large file sizes may be an issue), it may be desirable to scan the image area only at the appropriate resolution for its size, and then scan the entire mount at a resolution that achieves 4,000 pixels across the long dimension.

Table 3.6.4

Aerials: Transmissive Originals (Film, Slides, and Negatives)
Features of Original Object	Digital Master File
NOTE: If scans of aerial photography will be used for oversized reproduction, follow the scanning recommendations for the next largest format (e.g., if your original is 70 mm wide, follow the specifications for 127 mm wide roll film to achieve 8,000 pixels across the long dimensions).
Format range: 70 mm wide and medium format roll film Size range: Smaller than 10 in. square	Pixel array: 6000 pixels across long dimension of image area, excluding mounts and borders. Resolution: Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 2700 PPI for 70mm originals and ranging down to the appropriate resolution to produce the desired size file from larger originals. Bit depth: 8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file . -or- 24-bit RGB mode for color and monochrome (stained negatives), can be produced from a 48-bit RGB file.
Format range: 127mm wide roll film, 4x5 in. and up to 5x7 in. sheet film Size range: Equal to or larger than 10 in. and up to 35 in. square	Pixel array: 8000 pixels across long dimension of image area, excluding mounts and borders. Resolution: Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 1600 PPI for 4x5 in. originals and ranging down to approximately 1100 PPI for 5x7 in. originals. Bit depth: 8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file . -or- 24-bit RGB mode for color and monochrome (e.g. albumen prints or other historic print processes), can be produced from a 48-bit RGB file.
Format range: Larger than 127mm wide roll film and larger than 5x7 in. sheet film Size range: Equal to or larger than 35 in. square	Pixel array: 10000 pixels across long dimension of image area, excluding mounts and borders. Resolution: Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 2000 PPI for 5x5 in. originals and ranging down to the appropriate resolution to produce the desired size file from larger originals. Bit depth: 8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file . -or- 24-bit RGB mode for color and monochrome (e.g. albumen prints or other historic print processes), can be produced from a 48-bit RGB file.

Aerials: Transmissive Originals (Film, Slides, and Negatives)

Features of Original Object

Digital Master File

NOTE: If scans of aerial photography will be used for oversized reproduction, follow the scanning recommendations for the next largest format (e.g., if your original is 70 mm wide, follow the specifications for 127 mm wide roll film to achieve 8,000 pixels across the long dimensions).

Format range:

70 mm wide and medium format roll film

Size range:

Smaller than 10 in. square

Pixel array:

6000 pixels across long dimension of image area, excluding mounts and borders.

Resolution:

Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 2700 PPI for 70mm originals and ranging down to the appropriate resolution to produce the desired size file from larger originals.

Bit depth:

8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file

-or-

24-bit RGB mode for color and monochrome (stained negatives), can be produced from a 48-bit RGB file.

Format range:

127mm wide roll film, 4x5 in. and up to 5x7 in. sheet film

Size range:

Equal to or larger than 10 in. and up to 35 in. square

Pixel array:

8000 pixels across long dimension of image area, excluding mounts and borders.

Resolution:

Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 1600 PPI for 4x5 in. originals and ranging down to approximately 1100 PPI for 5x7 in. originals.

Bit depth:

8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file

-or-

24-bit RGB mode for color and monochrome (e.g. albumen prints or other historic print processes), can be produced from a 48-bit RGB file.

Format range:

Larger than 127mm wide roll film and larger than 5x7 in. sheet film

Size range:

Equal to or larger than 35 in. square

Pixel array:

10000 pixels across long dimension of image area, excluding mounts and borders.

Resolution:

Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 2000 PPI for 5x5 in. originals and ranging down to the appropriate resolution to produce the desired size file from larger originals.

Bit depth:

8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file

-or-

24-bit RGB mode for color and monochrome (e.g. albumen prints or other historic print processes), can be produced from a 48-bit RGB file.

Table 3.6.5

Aerials: Reflective Originals
Features of Original Object	Digital Master File
NOTE: If scans of aerial photography will be used for oversized reproduction, follow the scanning recommendations for the next largest format (e.g., if your original is 8x10 in., follow the specifications for formats larger than 8x10 in. to achieve 6000 pixels across the long dimensions.
Format range: Smaller than 8x10 in. Size range: Smaller than 80 in. square	Pixel array: 4000 pixels across long dimension of image area, excluding mounts and borders. Resolution: Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 400 PPI for originals approximately 8x10 in. and ranging up to the appropriate resolution to produce the desired size file from smaller originals, approximately 570 PPI for 5x7 in. and 800 PPI for 4x5 in. originals. Bit depth: 8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file. -or- 24-bit RGB mode for color and monochrome (e.g. discolored prints), can be produced from a 48-bit RGB file.
Format range: Equal to or larger than 8x10 in. and up to 11x14 in. Size range: Equal to or larger than 80 in. square and up to 154 in. square	Pixel array: 6000 pixels across long dimension of image area, excluding mounts and borders. Resolution: Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 600 PPI for 8x10 in. originals and ranging down to approximately 430 PPI for 11x14 in. originals. Bit depth: 8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file . -or- 24-bit RGB mode for color and monochrome (e.g. albumen prints or other historic print processes), can be produced from a 48-bit RGB file.
Format range: Equal to or larger than 11x14 in. Size range: Equal to or larger than 154 in. square	Pixel array: 8000 pixels across long dimension of image area, excluding mounts and borders. Resolution: Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 570 PPI for 11x14 in. originals and ranging down to the appropriate resolution to produce the desired size file from larger originals. Bit depth: 8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file . -or- 24-bit RGB mode for color and monochrome (e.g. albumen prints or other historic print processes), can be produced from a 48-bit RGB file.

Aerials: Reflective Originals

Features of Original Object

Digital Master File

NOTE: If scans of aerial photography will be used for oversized reproduction, follow the scanning recommendations for the next largest format (e.g., if your original is 8x10 in., follow the specifications for formats larger than 8x10 in. to achieve 6000 pixels across the long dimensions.

Format range:

Smaller than 8x10 in.

Size range:

Smaller than 80 in. square

Pixel array:

4000 pixels across long dimension of image area, excluding mounts and borders.

Resolution:

Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 400 PPI for originals approximately 8x10 in. and ranging up to the appropriate resolution to produce the desired size file from smaller originals, approximately 570 PPI for 5x7 in. and 800 PPI for 4x5 in. originals.

Bit depth:

8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file.
-or-
24-bit RGB mode for color and monochrome (e.g. discolored prints), can be produced from a 48-bit RGB file.

Format range:

Equal to or larger than 8x10 in. and up to 11x14 in.

Size range:

Equal to or larger than 80 in. square and up to 154 in. square

Pixel array:

6000 pixels across long dimension of image area, excluding mounts and borders.

Resolution:

Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 600 PPI for 8x10 in. originals and ranging down to approximately 430 PPI for 11x14 in. originals.

Bit depth:

8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file

-or-

24-bit RGB mode for color and monochrome (e.g. albumen prints or other historic print processes), can be produced from a 48-bit RGB file.

Format range:

Equal to or larger than 11x14 in.

Size range:

Equal to or larger than 154 in. square

Pixel array:

8000 pixels across long dimension of image area, excluding mounts and borders.

Resolution:

Adjust the scan resolution to meet pixel array specifications, based on the format of the original object – approximately 570 PPI for 11x14 in. originals and ranging down to the appropriate resolution to produce the desired size file from larger originals.

Bit depth:

8-bit grayscale mode for black-and-white, can be produced from a 16-bit grayscale file

-or-

24-bit RGB mode for color and monochrome (e.g. albumen prints or other historic print processes), can be produced from a 48-bit RGB file.

Table 3.6.6

Objects and Artifacts

10 to 16 megapixel 24-bit RGB mode image, can be produced from a 48-bit RGB file. If scanning photographic copies of objects and artifacts, see recommended requirements in the appropriate photo charts above (Tables 3.6.2-3.6.3).

Document Owner: California Digital Library

Last reviewed: April 2008

URL: http:// www.cdlib.org/inside/diglib/guidelines/bpgimages/reqs.html

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