Non-Photo Blue

Colour coordinates
Hex triplet	#A4DDED
sRGB^B (r, g, b)	(164, 221, 237)
HSV (h, s, v)	(193°, 31%, 93%)
CIELCh_uv (L, C, h)	(85, 34, 214°)
Source	^[Unsourced]
ISCC–NBS descriptor	Very light greenish blue
B: Normalized to [0–255] (byte)

(1) Colour copy of non-photo blue pencil. (2) Colour copy of blue pen. (3) Grayscale copy of non-photo blue pencil. (4) Grayscale copy of blue pen.

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 printer 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.

Change in function

More recently, with digital 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 causes the blue to disappear. 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.

Black ink

The difference between the non-photo blue and black ink is great enough that digital image manipulation can separate the two easily. If a black-and-white bitmap setting is scanned in, the exposure or threshold number can be set high enough to detect the black ink or dark images being scanned, but low enough to leave out the non-photo blue. On a threshold scale of 0–255, this number would be approximately 140. Only with a considerably low threshold setting will the blue be detected; this however may greatly distort black lines and add a lot of noise and black speckles, making the image potentially almost unrecognizable. Scanning in black-and-white makes it possible for the non-photo blue still to serve its original purpose, as notes and rough sketching lines can be placed throughout the image being scanned and remain undetected by the scan head.

References

^ Colleen Doran (8 November 2007). Manga Pro Superstar Workshop: How to Create and Sell Comics and Graphic Novels. IMPACT. pp. 14–. ISBN 978-1-58180-985-5. Retrieved 2 January 2013.
^ Freddie E Williams II (1 September 2009). The DC Comics Guide to Digitally Drawing Comics. Random House Digital, Inc. pp. 52–. ISBN 978-0-8230-9923-8. Retrieved 2 January 2013.

Shades of blue

Aero	Air Force blue	Air superiority blue	Alice Blue	Argentinian Blue	Azure	Azul	Baby blue	Berkeley Blue	Bice blue

Bleu de France	Blue	Blue-gray	Bondi blue	Brandeis blue	Byzantine blue	Cambridge blue	Carolina blue	Celestial Blue	Celtic Blue

Cerulean	Chefchaouen Blue	Chrysler blue	Cobalt blue	Columbia blue	Cornflower	Blue (Crayola)	Dark blue	Deep Sky Blue	Delft Blue

Denim	Dodger blue	Duke blue	Egyptian blue	Federal blue	Glaucous	Green-blue	Electric indigo	Eclipse	French blue

Honolulu blue	Ice blue	Illini blue	Indigo	Indigo dye	International Klein Blue	Jordy Blue	Lapis Lazuli	Light blue	Light Sky Blue

Majorelle Blue	Marian blue	Maya blue	Medium blue	Medium slate blue	Midnight blue	Blue (Munsell)	Navy blue	Blue (NCS)	Neon blue

Non-photo blue	Oxford Blue	Palatinate blue	Pale azure	Penn Blue	Periwinkle	Persian blue	Phthalo blue	Picton Blue	Polynesian blue

Powder blue	Prussian blue	Resolution Blue	RISD Blue	Royal Blue (web color)	Royal blue (traditional)	Ruddy Blue	Sapphire	Savoy blue	Silver Lake Blue

Sky blue	Space cadet	Steel blue	Tang Blue	True Blue	Tufts Blue	UCLA Blue	Ultramarine	United Nations Blue	Uranian Blue

Violet-blue	Vista Blue	Yale Blue	YInMn Blue	Zaffre

Change in function

Black ink

See also

References