org.hd.d.pg2k.svrCore.mediahandler
Class jpg

java.lang.Object
  org.hd.d.pg2k.svrCore.MIME.AbstractHandler
      org.hd.d.pg2k.svrCore.MIME.AbstractImageHandler
          org.hd.d.pg2k.svrCore.mediahandler.jpg

All Implemented Interfaces:

Handler

public final class jpg
extends AbstractImageHandler

Default handler for jpg file (MIME type image/jpeg).

TARGET_BPP

private static final int TARGET_BPP

Target bits-per-pixel for thumbnail images; strictly positive. Does not need to leave all images perfect, but most should be OK. Note that we'll be limited from above by the absolute size limits of thumbnails in general.

A value in the range 2--4 is probably good.

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Constant Field Values

FILE_OVERHEAD

private static final int FILE_OVERHEAD

Estimated JPEG overhead constant, ie what would a 0x0 JPEG file size be; non-negative. This factor helps avoid penalising small images by having the overhead eat into the bits that should be being used by the image.

One byte less than a 1x1 white image produced by PSP7.

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Constant Field Values

maxJPEGQuality

private static final int maxJPEGQuality

Max quality allowed in a JPEG montage or thumbnail. We don't go to 100%, since that might inflate the image and gives hardly any image improvement.

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Constant Field Values

normalThumbnailJPEGQuality

private static final int normalThumbnailJPEGQuality

Normal/initial quality for a JPEG thumbnail. This is reasonable for most images, though erring slightly on the side of retention of image quality at cost of download speed.

A quality of 75% is the default for the JPEG encoder.

A value from 50--90 is probably good; 85 has worked well in the past.

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Constant Field Values

minJPEGQuality

private static final int minJPEGQuality

Min quality allowed in a JPEG montage or thumbnail. We don't go to 0%, since the image would be unusable.

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Constant Field Values

EST_BYTES_PER_IMAGE_PIXEL_IN_MEMORY

private static final int EST_BYTES_PER_IMAGE_PIXEL_IN_MEMORY

Estimated (maximum) bytes per pixel of a decoded image in memory. This assumes that a 24-bit RGB or ARGB format is the most expensive we will run across. (The other main possibility is an 8-bit greyscale.)

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Constant Field Values

thumbnailParams

private static final Handler.ThumbnailParams thumbnailParams

Gather together thumbnail parameters.

EXIF

private static final int EXIF

Type of EXIF segment in JPEG.

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Constant Field Values

IPTC

private static final int IPTC

Type of IPTC segment in JPEG.

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Constant Field Values

MAX_VALUE_CHARS

private static final int MAX_VALUE_CHARS

Longest value (chars) we will accept without discarding; strictly positive.

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Constant Field Values

jpg

public jpg()

getExhibitType

public ExhibitMIME.ExhibitTypeParameters getExhibitType()

Get internal type of ExhibitMIME type; never null.

get2DImageDimensions

public java.awt.Dimension get2DImageDimensions(java.io.InputStream is)
                                        throws java.io.IOException

Get dimensions X and Y of a JPEG exhibit, else null if dimensions cannot be computed. This reads the opening bytes of the exhibit directly to extract the dimensions, rather than loading and interpreting the whole image.

This input stream must be of the correct type, eg the magic number already checked.

This does not close its input stream when done.

Specified by:

get2DImageDimensions in interface Handler

Overrides:

get2DImageDimensions in class AbstractImageHandler

Parameters:

is - the exhibit as a binary data stream

Throws:

java.io.IOException - in case of problems with corrupt data (or a broken exhibit)

canMakeThumbnails

public boolean canMakeThumbnails()

Returns true if this can make thumbnail/sample exhibits for this type. Returns true because we can make JPEG thumbnails.

Specified by:

canMakeThumbnails in interface Handler

Overrides:

canMakeThumbnails in class AbstractImageHandler

getThumbnailParams

public Handler.ThumbnailParams getThumbnailParams()

Get ThumbnailParameters for JPEG handler.

Specified by:

getThumbnailParams in interface Handler

Overrides:

getThumbnailParams in class AbstractHandler

extractSpecificImageMetaData

protected org.w3c.dom.Node extractSpecificImageMetaData(javax.imageio.metadata.IIOMetadata imageMetadata,
                                                        Name.ExhibitFull exhibitName)

Get specific (image) metadata for one particular image type; null if none. This does not have to be provided, but if so enables such things as EXIF and IPTC extraction from JPEG images.

We trim and normalise values shown a little, and discard any huge values, since this data is intended for a human to read. If they need more detail then they can download the image and open it in a decent Photoshop-like app.

This may be a mix of stream and image/frame metadata.

Overrides:

extractSpecificImageMetaData in class AbstractImageHandler

Parameters:

imageMetadata - imageio portable metadata for this exhibit; never null

exhibitName - full exhibit name (primarily to help with debugging); never null