What is PSD

PSD is a proprietary file format used to create and edit images in Adobe Photoshop. It is a widely accepted format as it supports all available image types – Bitmap, RGB, Duotone, Grayscale, Indexed Color, CMYK, Lab, and Multichannel.

The biggest advantage of using the PSD format is that it can save images in layers (image, text, shape, etc.). In other words, the image may be opened with Adobe Photoshop anytime at a later date and each individual layer, or part, may be adjusted and edited independently to achieve better effects. Special blending effects may also be achieved using the transparency mask of Photoshop. These special features have made PSD a very useful format for further adjustment and manipulation of an image in desktop publishing. Even those designers who work with other image file types like TIFF, first work on their images in Photoshop, then transfer them to their preferred file types.

PSD files are usually large because of the layers, but the size may be reduced by cropping the individual layers of the image. But cropping has a disadvantage – it limits the ability to edit. Leaving images uncropped may make files large but it has its advantages – the parts that fall outside the cropping bounds are still written inside the PSD file, and can be revealed by increasing the size of the Photoshop canvas.
The maximum size of a PSD file (with file extension of ‘.psd’) is 30,000x30,000 pixels and may be saved with 16 bits per color channel.

The PSD format is divided into five sections. The first is the header which specifies the image size and color channels; the second contains the color mode data; the third contains the image resources; the fourth has the layer and mask information; and the final section contains the image data.

PSD image files may be opened with Adobe Photoshop or Photoshop Elements on Windows; and Adobe Photoshop, Photoshop Elements, or Apple Preview on Mac OS.