Colours and File types

When designing your postcard or letter there are a lot of different formats of images that can be used and settings that can be utilised. As you're designing your mail for the intention of printing there are certain recommendations and requirements to follow.

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Colour

Most images created via a computer will default to the RGB colour profile. The RGB colour profile is represented as combinations of the three primary colours of light: Red, Green, and Blue. The RGB colour model is widely used in various digital displays, such as computer monitors, televisions, and digital cameras, because it corresponds to the way human vision perceives colour.

However, when designing for print RGB is not suitable as RGB is designed for displays that emit light, whereas printing requires a subtractive colour model like CMYK (Cyan, Magenta, Yellow, Black). Therefore, your design could run into the following issues:

• Brightness and Saturation:

  • Bright and highly saturated colours in RGB may appear duller in CMYK. For example, vivid blues and greens might lose their intensity.

• Colour Shifts:

  • Certain colours, like neon or very bright reds and greens, might shift to different hues. This is because those colours cannot be accurately represented within the CMYK colour space.

• Detail and Contrast:

  • Some detailed and high-contrast areas might lose definition, especially in the highlights and shadows, due to differences in how RGB and CMYK handle tonal ranges.

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Format - JPEG / PNG

While processing your mail we will always prefer JPEG images over PNGs. PNGs can result in larger file size which can result in slower processing time and potential delays with larger volumes of mail.

To go into greater detail, here are several benefits to using JPEG images:

• Efficient Compression:

  • Lossy Compression: JPEG uses lossy compression, which reduces file size by selectively discarding less critical image data. This process is optimized for human vision, which is less sensitive to small changes in colour and brightness.
  • DCT (Discrete Cosine Transform): JPEG compression uses DCT to transform the image into frequency components. High-frequency details, which are less noticeable to the human eye, are more heavily compressed, resulting in smaller file sizes without significant visible quality loss.

• Perceptual Coding:

  • Human Vision Model: JPEG compression is based on a model of human vision, which means it prioritizes retaining details that are more perceptible to the human eye, such as contrasts and edges, while discarding information that is less noticeable.

• Colour Subsampling:

  • Chroma Subsampling: JPEG often uses chroma subsampling, where the colour information is sampled at a lower resolution than the brightness information. Since the human eye is more sensitive to brightness changes than colour changes, this technique reduces file size with minimal perceptible impact on image quality.