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Colour Space: sRGB/sRGBA and CMYK

A defined set of colours is known as a colour space or colour gamut. Three examples are, sRGB, CMYK and CIE 1931 color space. sRGB colours are created by combining red, blue or green light and is the prevailing standard in the TV and computer industry. The printing industry needs to subtract light, eg white paper, by using ink. The colour that a surface displays depends on which parts of the visible spectrum are not absorbed and therefore remain visible. CIE 1931 RGB are the perceived colours in human vision.

The RGB of sRGB stands for Red, Green, Blue while the 's' means standard. In computer terms each are known as a channel. The 'A' stands for Alpha and is an optional channel which handles transpancy.

D65 is the colour sRGB uses for white. It corresponds roughly to a midday sun. The 65 is 6503.6K on the colour temperature scale.

Over 16.7 million colours can be created by combining 256 of all three colours (256 x 256 x 256). This set of 16.7 million colours are known as true color or 24-bit color. Each colour is numbered 0-255. It is like each light is on a dimmer. Turning all three lights off creates black (0,0,0). Turning all three lights on, creates white (255,255,255). Turning on just the red (255, 0, 0) yeilds red, etc. To get the zco.mx orange the red light is on, 255; the green light is 102 of 255 of the way on and the blue light is off; 255,102,0. In hexadecimal (hex), 255 equals 0xFF, 102 is 0x66 and 0 is 0x00.

decimal hexadecimal colour
0, 0, 0 #000000 Black
255, 255, 255 #FFFFFF White
255, 0, 0 #FF0000 Red
0, 255, 0 #00FF00 Green
0, 0, 255 #0000FF Blue
255, 102, 0 #FF6600 zco.mx

cmyk_vs_rgb.jpg CMYK
The four colours used in the printing industry are cyan, magenta, yellow; as well as a key colour, black. This colour space is named CMYK. CMYK does completely overlap with sRGB as well it can't represent the brightness of sRGB colours and thus its colours can look quite different. Instead of numbers CMYK uses percentages. It's the percentage of pigment needed to be added to white in order to create the colour. 0%, 0%, 0%, 0% is white, 100%, 0%, 0%, 0% is cyan, etc.

Working Image File Formats

Pros and Cons: PSD vs TIFF

+ psd - can store much more information, including reversible edits to layers

+ psd - can store text, ie text in speech bubbles

+ psd - work well with all Adobe software, eg layers work in InDesign

- psd - file sizes are now only slightly larger compared to TIFF

+ tiff - most OSes can read TIFF without special software, unlike psd

+ tiff - can store layers

Conclusion: The pros for PSD outweigh the pros for TIFF.

Images For the Web/cbz (RGB)

Pros and Cons: PNG vs JPEG vs GIF

+ png - lossless - Lossless means there is no loss in image quality.

+ png - transparency - The transparency information is stored in a separate channel called the alpha channel (A). If a png has a colour space of RGB, then there is no transparency. If a png has a colour space of RGBA, then the image is making use of the alpha channel.

- png - slightly larger file sizes - The png file format produce the best image quality (lossless) and so the trade off is a larger file size. Although the file sizes of PNG and JPEG are comparable one can further decrease the file size of PNGs using a program called pngcrush (win | mac | linux) and still maintain lossless image quality.

+ jpg - smallest file sizes - If image quality isn't of most importance then JPEGs could be used, eg sharing large photos on the web.

- jpg - loss of quality (lossy) - The biggest drawback to the JPEG format is loss of quality. When an image is exported to JPEG artifacts and blurring will occur. If that image is then resized and saved as JPEG it will become more distorted.

+ gif - animation - The GIF file format supports the ability to loop through a set of images.

- gif - deprecated - any image that isn't animated should use PNG. PNG images have smaller files, are a more modern format and have better support in image viewers.

Conclusion: Since most comic art images will be either 256 colour or 256 grayscale, then PNG8 file format would best.

TIFF w/SWOP embedded

Every print shop will have their own workflow and thus the file format they ask for can vary. One common file format is TIFF w/SWOP embedded.

NOTE: CMYK shouldn't be used for web view/cbz. It's possible these images will crash, or look incorrect in, image viewer programs.