Grayscale images present the best opportunity for basic image enhancement. A modest amount of editing can yield substantial improvements in scanned image quality. A basic series of corrective steps are illustrated in the figures below.
These were performed with the Canoscan software but any can be used.
In a grayscale image each pixel represents one of 256 brightness levels with 0 being the least bright, (black) and 255 being the brightest, (white).
Image file size variation over 200 to 1 from 43K to 10MB ...
Resolution Table
The results of scanning a 4.6" x 4.3" grayscale image at different resolutions are presented below. The scans were saved in three common file formats to determine the corresponding file size and reproduction quality.
| File | Quality | Size | |||||
| Resolution | Format | Size¹ | Print² | Screen | Screen³ | Comment | |
| 100 spi | GIF | 174 KB | Excellent | 1.25x | Monitor only | ||
| JPG | 43 KB | Very Good | Monitor only | ||||
| 150 spi | JPG | 87 KB | Good | Very Good | 1x | 1.9x | Service & Collaborate |
| TIF | 329 KB | Good | Excellent | ||||
| 300 spi | JPG | 395 KB | Very Good | 2x | 3.75x | Service | |
| TIF | 1.1 MB | Excellent | 2x | 3.75x | Archive | ||
| 600 spi | JPG | 1.43 MB | Very Good | 4x | 7.5x | Enlargement | |
| TIF | 3.97 MB | Excellent | 4x | 7.5x | Enlargement | ||
| 1200 spi | JPG | 5.6 MB | Very Good | 8x | 15x | Enlargement | |
| TIF | 9.8 MB | Excellent | 8x | 15x | Enlargement | ||
¹ JPG images at 4:1 compression. TIF images are uncompressed.
² on a 600dpi inkjet printer.
³ on a 17" monitor @ 1024x800 resolution
Comment Key
- Thumbnail: small image, e.g. 100 pixels x 150 pixels, used for content preview.
- Collaborative: limited file size, e.g. < 200 KB, for efficient image transfer. Formats: GIF, PNG, JPG.
- Service: good-quality image intended for short-term use. May be compressed for efficient storage and transfer. Formats: GIF, PNG, JPG, TIF.
- Archive: lossless high-quality master image free of compression artifacts. Used for reproduction and long-term storage. Requires reprocessing as image standards change. Formats: TIF, PhotoCD.
Tone Adjustment
Histogram
The histogram shows a normal tonal distribution centered near the 50% gray level. The image lacks contrast however, the whitest highlight is over 20% and the darkest shadow is near 85%.
Whitepoint (highlight) adjustment
The whitepoint is set slightly to the right of the lightest tone in the image. This charges the highlights in the shirt from near 20% gray to about 3% gray.
Blackpoint (shadow) adjustment
The blackpoint is set at the darkest tone in the image for screen viewing. After adjustment the innertube will have some tones near 90% gray.
Midpoint (gamma)adjustment
A slight gamma adjustment emphasizes the some of the detail in the face and waves.
Filtering
Unsharp Masking
Unsharp masking is applied to restore some of the sharpness lost in scanning. This emphasizes some of the dust and scratches that can be reduced by using the Reduce Dust and Scratches filter. Other marks can be edited after scanning.
Before/After
Notes
- for images requiring extensive editing scan at 2x the desired resolution in color and save as TIF.
- to maintain highlight detail, especially when printing, the whitepoint should be set near the 4% level.
- to maintain shadow detail when printing the blackpoint should be set at a value that will allow for printer dotgain. The dotgain is a function of both ink and paper type.
- when possible, make adjustments with the scanning software.