PSD

Full Name	PSD (Adobe Photoshop)
Format ID	IG_FORMAT_PSD = 36
File Extension(s)	*.psd
Data Type	Raster Image
Data Encoding	Binary
Color Profile Support	Read, Write
Multi-Page Support	No
Alpha Channel Support	Yes (see Comments for more information).

ImageGear Supported Versions:

Version 2.0
Version 2.5
Version 3.0
Version 8.0

ImageGear Supported Features:

IG_FLTR_DETECTSUPPORT - autodetection
IG_FLTR_PAGEREADSUPPORT - single page file reading
IG_FLTR_PAGEINSERTSUPPORT - single-page file writing

ImageGear Read Support:

IG_COMPRESSION_DEFLATE:
- Indexed RGB: 1, 8 bpp;
- Grayscale: 8, 16 bpp;
- Grayscale + Alpha: 8, 16 bpp;
- Grayscale + Alpha + Extra: 8, 16 bpp;
- RGB: 24, 48 bpp;
- RGB + Alpha: 32, 64 bpp;
- RGB + Alpha + Extra 8, 16 bpc;
- CMYK: 32, 64 bpp;
- CMYK + Extra: 8, 16 bpc;
- Lab: 24, 48 bpp;
- Lab + Extra: 8, 16 bpc;
- HSL: 24, 48 bpp;
- HSL + Extra: 8, 16 bpc
IG_COMPRESSION_NONE:
- Indexed RGB: 1, 8 bpp;
- Grayscale: 8, 16 bpp;
- Grayscale + Alpha: 8, 16 bpp;
- Grayscale + Alpha + Extra: 8, 16 bpp;
- RGB: 24, 48 bpp;
- RGB + Alpha: 32, 64 bpp;
- RGB + Alpha + Extra 8, 16 bpc;
- CMYK: 32, 64 bpp;
- CMYK + Extra: 8, 16 bpc;
- Lab: 24, 48 bpp;
- Lab + Extra: 8, 16 bpc;
- HSL: 24, 48bpp;
- HSL + Extra: 8, 16 bpc
IG_COMPRESSION_RLE:
- Indexed RGB: 1, 8 bpp;
- Grayscale: 8, 16 bpp;
- Grayscale + Alpha: 8, 16 bpp;
- Grayscale + Alpha + Extra: 8, 16 bpp;
- RGB: 24, 48 bpp;
- RGB + Alpha: 32, 64 bpp;
- RGB + Alpha + Extra 8, 16 bpc;
- CMYK: 32, 64 bpp;
- CMYK + Extra: 8, 16 bpc;
- Lab: 24, 48 bpp;
- Lab + Extra: 8, 16 bpc;
- HSL: 24, 48 bpp;
- HSL + Extra: 8, 16 bpc

ImageGear Write Support:

IG_COMPRESSION_NONE:
- Indexed RGB: 1, 8 bpp;
- Grayscale: 8 bpp;
- Grayscale + Alpha: 16 bpp;
- Grayscale + Alpha + Extra: 8 bpc;
- RGB: 24 bpp;
- RGB + Alpha: 32 bpp;
- RGB + Alpha + Extra: 8 bpc;
- CMYK: 32 bpp;
- CMYK + Extra: 8 bpc;
- Lab: 24 bpp;
- Lab + Extra: 8 bpc
IG_COMPRESSION_PACKED_BITS:
- Indexed RGB: 1, 8 bpp;
- Grayscale: 8 bpp;
- Grayscale + Alpha: 16 bpp;
- Grayscale + Alpha + Extra: 8 bpc;
- RGB: 24 bpp;
- RGB + Alpha: 32 bpp;
- RGB + Alpha + Extra: 8 bpc;
- CMYK: 32 bpp;
- CMYK + Extra: 8 bpc;
- Lab: 24 bpp;
- Lab + Extra: 8 bpc

ImageGear Filter Control Parameters:

Filter Control Parameter	Type	Default Value	Available Values	Description
LOAD_FIRST_EXTRA_CHANNEL_AS_ALPHA	AT_BOOL	FALSE	TRUE, FALSE	This parameter specifies how ImageGear should load the first extra channel of a PSD image. If FALSE, ImageGear loads all extra channels according to their descriptors in the file header. If the channel contains transparency information, ImageGear loads it as Alpha channel. Otherwise ImageGear loads it as Extra channel. If TRUE, ImageGear loads first extra channel as Alpha channel. This mode provides backward compatibility with previous versions of ImageGear.
READ_LAYER_INDEX	INT	-1	Any integer, but no more than number of layers	When > -1 specifies a zero based index of layer mask image to load, otherwise reads the composition image.
READ_LAYER_MASK	AT_BOOL	FALSE	FALSE, TRUE	When TRUE PSD layer mask images are loaded as usual pages of multi-page file, otherwise layer masks are ignored.
READ_LAYERS	AT_BOOL	TRUE	TRUE, FALSE	Affects the reading of PSD images that contain layers. If TRUE, ImageGear reads the composition image and image layers. If FALSE, ImageGear only reads the composition image. See Image Layers.
SAVE_THUMBNAIL	AT_BOOL	FALSE	FALSE, TRUE	Gets/Sets thumbnail flag. If TRUE then thumbnail will be added to image.
THUMBNAIL_ENABLE	AT_BOOL	FALSE	FALSE, TRUE	When TRUE thumbnail reading function loads thumbnail image provided by PSD format.
THUMBNAIL_HEIGHT	UINT	64	Any positive value	Gets/Sets thumbnail height.
THUMBNAIL_WIDTH	UINT	64	Any positive value	Gets/Sets thumbnail width.

Comments:

The PSD file is considered by many in the computer graphics arts community as an industry standard.

The PSD is organized into 5 major segments of data: the header, 3 informational blocks, and the bitmap data. The short header always contains a "signature" of 8PPS, as well as these fields: width, height, and bit depth of the bitmap.

The first block of informational data is called the "Color Mode Data Block". It begins with a value for the length of the block. If the image has a palette, it is located here.

The next block is called the "Image Resources Block". Like the previous block, it first gives the length of the block. An ID field is filled with one of many possible values that indicate the structure where the data is stored. It may contain such parameters as resolution.

The last informational block is called the "Layer and Mask Instruction Block". After a value for the length of the block, it tells how many "layer records" follow. There is a record for each layer in the image. Each record begins with a channel ID and the length of the data in the record. After the records, a "Layer Mask" section may be stored, if applicable.

The bitmap data represents the last segment of a PSD file.

For historic reasons, ImageGear uses the IG_COMPRESSION_PACKED_BITS constant for saving Packed Bits compressed PSD images, and uses the IG_COMPRESSION_RLE constant to report Packed Bits compression when reading PSD images. For the PSD format, the terms "Packed Bits" and "RLE" are used synonymously.

The term "Alpha channel" has a different meaning in ImageGear and Adobe Photoshop. In ImageGear, Alpha channel defines the opacity/transparency of an image. Only one Alpha channel per image can exist. This corresponds to "Transparency" information in PSD and PSB formats. In Photoshop, "Alpha channels" are used for storing masks (grayscale images that define areas to be edited or protected from editing). ImageGear uses Extra channels for this purpose. Please see Spot and Mask Channels for more information.

References Used

Murray, James D. and William vanRyper. Encyclopedia of Graphics File Formats, 2d ed. Sebastopol, CA: O'Reilly & Associates, Inc., 1996.