Non-photo blue
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| Non-photo blue | |
|---|---|
 Colour coordinates | |
| Hex triplet | #A4DDED |
| sRGBB (r, g, b) | (164, 221, 237) |
| HSV (h, s, v) | (193°, 31%, 93%) |
| CIELChuv (L, C, h) | (85, 34, 214°) |
| Source | [Unsourced] |
| ISCC–NBS descriptor | Very light greenish blue |
| B: Normalized to [0–255] (byte) | |
Non-photo blue (or non-repro blue) is a common tool in the graphic design and print industry,[1][2] being a particular shade of blue that cannot be detected by graphic arts camera film. This allows layout editors to write notes to the print operator on the print flat (the image that is to be photographed and sent to print) which will not show in the final form. It also allows artists to lay down sketch lines without the need to erase after inking.
More recently, with digital image scanning and image manipulation, non-photo blue fulfills its function in a different way. The artist can do their sketch and inking in the traditional manner and scan the page. Most scanners will detect the light blue lines. However, shifting to greyscale and increasing the contrast and brightness of the scanned image reduces the appearance of the blue tones. Another common approach involves replacing the blue channel with another channel – typically the red channel. The exact processes may differ depending on the scanner, settings and image-editing software, but the concept remains the same.