ImageMan ActiveX
JPG Image Format

Description

Short for Joint Photographic Experts Group. JPEG is a lossy compression technique for color images. Although it can reduce files sizes to about 5% of their normal size, some detail is lost in the compression.

Import Library

im8jpg.dil

Export Library

 im8xjpg.del

Remarks

 Supports JFIF compliant files. LOSSY_QUALITY can be set for JPEG images. Currently reads both 8 and 24 bit images writes only 24 bit color and 8 bit gray-scale images. Progressive JPG images are supported.

Attributes

 

Read and Write

Name

Data Type

Notes

EXTENSION

String

"JPG"

THUMBNAIL

Binary

This attribute is not automatically loaded. Raw binary JFIF version 1.1 thumbnail information

COMMENT

Binary

This attribute is not automatically loaded. Comment data may contain embedded NULL 0

JPEG_APP%d

Binary

This attribute is not automatically loaded.

Where %d is an app marker between 0 and 15. JFIF uses APP0 and Adobe uses APP14 so beware of replacing critical data

 

JPEG_COLORSPACE

String

This attribute will be defined as the default value unless specifically defined.

"JFIF_YCBCR"|"JFIF_GRAYSCALE_YCBCR"|"ADOBE_AP14_RGB"|"ADOBE_AP14_CMYK"|"ADOBE_AP14_YCCK"

 

JPEG_DCT_METHOD

String

DCT_ISLOW|DCT_IFAST|DCT_FLOAT

(default ISLOW) Fast will yield unacceptable results in most situations. DCT_FLOAT, while it yields slightly better results in some cases, will be slower unless you have a good FP processor, also results will vary depending on you FP processor. DCT_ISLOW is the best choice in most situations and is consistent across machines.

 

JPEG_PROGRESSIVE

Boolean

JPEG_OPTIMIZE_CODING

Boolean

Note: while this option will make your image slightly smaller it will take twice as long because it needs to be done in two passes.

JPEG_JFIF_VERSION_MAJOR

 Int8

If you write a Thumbnail you should make sure Major and Minor are 1.1

JPEG_JFIF_VERSION_MINOR

Int8

LOSSY_QUALITY

Int32

Range between 1 and 99 defaults to 75

 

Write Only

JPEG_SMOOTHING

int32

0 to 100.default 0 which is no smoothing good for dithered images

JPEG_RESTART_INTERVAL

Int32

no clamping, use with caution, checking pass in valid entries

(0 is default which means no restart unless RESTART_ROWS is set) exact interval in MCU blocks don't use this unless you know what you are doing if you set JPEG_RESTART_ROWS it will calculate the RESTART_INTERVAL based on that value overriding this setting.

 

JPEG_RESTART_ROWS

Int32

There is no clamping provided, so use with caution, allowing checking to pass in valid entries.

(0 is default which means no restart unless RESTART_INTERVAL is set) 1 Restart marker for one MCU row is often a good choice. The overhead of restart markers is higher in Grayscale JPEG files and MUCH higher in progressive JPEGS. If you use restarts you may want to use larger intervals in these cases.

 

JPEG_RESTART_ROWS

0 - IMG HEIGHT

 

 


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