The .PSD (Photoshop Document) format stores an image with support for most imaging options available in Adobe Photoshop program. These include layers with masks, color spaces, ICC profiles, transparency, text, alpha channels, etc. Loading and saving of indexed, grayscale, RGB(A), HDR (FP32), and CMYK (auto converted to RGB) images is supported. Non-HDR gray, RGB, and CMYK images can have 8bit or 16bit color channels. There is no support for loading mono images, duotone images are treated like grayscale images, and multichannel and CIE Lab images are loaded as RGB images but without actual conversion to RGB color space. Also no layer information is loaded. As of Imaging version 0.26.2 images with alpha channel can be saved using layers. That way when opened in Photoshop they have proper transparency, not alpha channel (will have one layer, RGB color channels, and transparency). PSD files with layers are bigger because image has to be stored as background as well as layer data. Therefore, RLE compression was implemented to keep the files smaller (Photoshop saves PSDs RLE compressed too by default). Note that layers are not supported for floating point image data formats since it's not supported by Photoshop itself. Saving of layers can also be disabled (will be opened in PS as background raster with RGBA channels) using appropriate option.

Format	TImageFormat equivalent	Loading	Saving	8 bit indexed	ifIndex8	Yes	Yes	24 bit RGB	ifR8G8B8	Yes	Yes	48 bit RGB	ifR16G16B16	Yes	Yes	32 bit ARGB	ifA8R8G8B8	Yes	Yes	64 bit ARGB	ifA16R16G16B16	Yes	Yes	8 bit grayscale	ifGray8	Yes	Yes	16 bit grayscale	ifGray16	Yes	Yes	16 bit grayscale + alpha	ifA8Gray8	Yes	Yes	32 bit grayscale + alpha	ifA16Gray16	Yes	Yes	32 bit R FP32	ifR32F	Yes	Yes	128 bit ARGB FP32	ifA32B32G32R32F	Yes	Yes	other types	depends on type	Yes/No	No

When working with PSD files you can find useful some options which can be set by SetOption function and their current values can be get by GetOption function. Or you can set them by modifying properties of TPSDFileFormat class.

OptionId	Allowed Values	Usage	ImagingPSDSaveAsLayer	0 (false) or 1 (true)	If enabled image data is saved as layer of PSD file. This is required to get proper transparency when opened in Photoshop for images with alpha data (will be opened with one layer, RGB color channels, and transparency). If you don't need this Photoshop compatibility turn this option off as you'll get smaller file (will be opened in PS as background raster with RGBA channels) Default value is 1 (true).