Adobe PSD

Full Name	PSD (Adobe Photoshop)
Format ID	ImGearFormats.PSD
File Extension(s)	*.psd
Data Type	Raster Image
Data Encoding	Binary
IG Multipage Support	No
IG Alpha Channel Support	Supports pre-multiplied Alpha and additional Alpha mask channels as ImageGear Extra channels.
IG Platforms Support	WIN32, WIN64, Linux32, Linux64, MAC32, MAC64

ImageGear Supported Versions

Version 2.0
Version 2.5
Version 3.0
Version 8.0

ImageGear Supported Features

DETECTSUPPORT - autodetection
PAGEREADSUPPORT - single page file reading
MPAGEREADPSUPPORT - multi-page file reading
PAGEINSERTSUPPORT - single-page file writing

ImageGear Read Support

ImGearCompressions.NONE:
- Indexed RGB: 1, 8 bpp;
- Grayscale: 8, 16 bpp;
- Grayscale + Alpha: 8, 16 bpc;
- RGB: 24, 48 bpp;
- RGB + Alpha: 32, 64 bpp;
- RGB + Alpha + Extra: 8, 16 bpc;
- RGB + Extra: 8, 16 bpc;
- CMYK: 32, 64 bpp;
- CMYK + Alpha: 40, 80 bpp;
- CMYK + Alpha + Extra: 8, 16 bpc;
- CMYK + Extra: 8, 16 bpc;
- LAB + Alpha: 32, 64 bpp;
- Lab + Alpha + Extra: 8, 16 bpc;
- Lab + Extra: 8, 16 bpc;
- HSL + Alpha: 32, 64 bpp;
- HSL + Alpha + Extra: 8, 16 bpc;
- HSL + Extra: 8, 16 bpc;
ImGearCompressions.PACKED_BITS:
- Indexed RGB: 1, 8 bpp;
- Grayscale: 8, 16 bpp;
- Grayscale + Alpha: 8, 16 bpc;
- RGB: 24, 48 bpp;
- RGB + Alpha: 32, 64 bpp;
- RGB + Alpha: + Extra 8, 16 bpc;
- RGB + Extra: 8, 16 bpc;
- CMYK: 32, 64 bpp;
- CMYK + Alpha: 40, 80 bpp;
- CMYK + Alpha + Extra: 8, 16 bpc;
- CMYK + Extra: 8, 16 bpc;
- LAB + Alpha: 32, 64 bpp;
- Lab + Alpha + Extra: 8, 16 bpc;
- Lab + Extra: 8, 16 bpc;
- HSL + Alpha: 32, 64 bpp;
- HSL + Alpha + Extra: 8, 16 bpc;
- HSL + Extra: 8, 16 bpc;

ImageGear Write Support

ImGearCompressions.NONE:
- Indexed RGB: 1, 8 bpp;
- Grayscale: 8 bpp;
- Grayscale + Extra: 8 bpp;
- Grayscale + Alpha: 8 bpp;
- Grayscale + Alpha + Extra: 8 bpp;
- RGB: 24 bpp;
- RGB + Extra: 8 bpc;
- CMYK: 32 bpp;
- CMYK + Extra: 8 bpc;
ImGearCompressions.PACKED_BITS:
- Indexed RGB: 1, 8 bpp;
- Grayscale: 8 bpp;
- Grayscale + Extra: 8 bpp;
- Grayscale + Alpha: 8 bpp;
- Grayscale + Alpha + Extra: 8 bpp;
- RGB: 24 bpp;
- RGB + Extra: 8 bpc;
- CMYK: 32 bpp;
- CMYK + Extra: 8 bpc;

ImageGear Filter Control Parameters

Filter Control Parameter

Type

Default Value

Available Values

Description

LoadFirstExtraChannelAsAlpha

boolean

false

false, true

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 IG loads it as Extra channel.

If true, IG loads first extra channel as Alpha channel. This mode provides backward compatibility with previous versions of ImageGear.

ReadLayerIndex

int

-1

Any integer, but no more than the number of layers

When > -1 specifies a zero based index of layer mask image to load, otherwise reads the composition image.

Non-Image Data Structure

Adobe PSD file format has different non-image data that can be stored before and after an image data. The Adobe PSD metadata design allows reading and writing the following non-image data.

Tag Name	Tag ID	Description
Signature	ImGearPSDTagIDs.SIGNATURE	Adobe Photoshop Signature: always equal to '8BPS'.
Version	ImGearPSDTagIDs.VERSION	Version: always equal to 1.
Rows	ImGearPSDTagIDs.ROWS	The height of the image in pixels. Supported range is 1 to 30,000.
Cols	ImGearPSDTagIDs.COLS	The width of the image in pixels. Supported range is 1 to 30,000.
Depth	ImGearPSDTagIDs.DEPTH	Depth: the number of bits per channel. Supported values are 1, 8, and 16.
ColorMode	ImGearPSDTagIDs.MODE	The color mode of the file. Supported values are: Bitmap = 0; Grayscale = 1; Indexed = 2; RGB = 3; CMYK = 4; Multichannel = 7; Duotone = 8; Lab = 9.
ColorModeLength	ImGearPSDTagIDs.MODE_LEN	The length of the following color data provided by tag ColorData.
ColorData	ImGearPSDTagIDs.COLOR_DATA	The color data.
PhotoshopResources	ImGearPSDTagIDs.PHOTOSHOP_RESOURCES	Photoshop Image Resource metadata group. Image resources are used to store non-pixel data associated with images.
Layers	ImGearPSDTagIDs.LAYERS	Photoshop Image Layer Info metadata group. Represents high-level organization of the layers information.
LayerCount	ImGearPSDTagIDs.LAYER_COUNT	Number of layers in the Photoshop Image.
Header	ImGearPSDTagIDs.HEADER	This section contains the basic properties of the image.
RESERVED_HDR	ImGearPSDTagIDs.RESERVED_HDR	Reserved: must be zero.
Channels	ImGearPSDTagIDs.CHANNELS	The number of channels in the image, including any alpha channels. Supported range is 1 to 56.
IPTC_NAA	ImGearPSDTagIDs.IPTC_NAA	File information (IPTC-NAA record 2).

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.

References Used

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