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

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

All Implemented Interfaces:

Handler

public final class png
extends AbstractImageHandler

Default handler for png file (MIME type image/png). Relies on Java Advanced Imaging extension JAI 1.1.2 or newer (javax.media.jai.*) for some functionality (eg making thumbnails); may not be able to run (or possibly even load) without it, though we try to ensure that basic functionality is available anyway.

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 4--8 is probably good.

See Also:

Constant Field Values

FILE_OVERHEAD

private static final int FILE_OVERHEAD

Estimated file overhead constant, ie what would a 0x0 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.

See Also:

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 24/32-bit RGB or ARGB format is the most expensive we will run across. (The other main possibility is an 8-bit greyscale.)

See Also:

Constant Field Values

maxThumbnailQuality

private static final int maxThumbnailQuality

Maximum quality allowed in a thumbnail; taken to be total colour depth. Assume that this is the same as the maximum number of bits in memory we expect an image to take.

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Constant Field Values

normalThumbnailQuality

private static final int normalThumbnailQuality

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

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Constant Field Values

minThumbnailQuality

private static final int minThumbnailQuality

Maximum quality allowed in a thumbnail; taken to be total colour depth. Must be positive and can be as little as monochrome, ie one bit.

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Constant Field Values

thumbnailParams

private static final Handler.ThumbnailParams thumbnailParams

Gather together thumbnail parameters.

png

public png()

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 PNG 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)

getThumbnailParams

public Handler.ThumbnailParams getThumbnailParams()

Description copied from class: AbstractHandler

Get ThumbnailParameters for a particular handler. A handler that does not build thumbnails (ie canMakeThumbnails() returns false) may return null for this, which is the default, but otherwise this should return non-null.

This is assumed to be fast, ie to return a fixed static instance for each handler.

This is protected, since only the support routines in this base class need access this data.

Specified by:

getThumbnailParams in interface Handler

Overrides:

getThumbnailParams in class AbstractHandler

canMakeThumbnails

public boolean canMakeThumbnails()

Returns true because handler can make thumbnails for this type.

Specified by:

canMakeThumbnails in interface Handler

Overrides:

canMakeThumbnails in class AbstractImageHandler

_reduceColoursQualityThreshold

protected int _reduceColoursQualityThreshold()

Description copied from class: AbstractImageHandler

Guide colour-reduction to reduce quality and size of lossless image formats. Defaults to -1, implying that the image format is a lossy format for which the ImageWriteParam.setCompressionQuality() mechanism is enough to trade encoded image size for quality.

Else this is a positive value n, typically 8 or 24, which sets a quality level at/below which the number of colours in the image is reduced to (capped at) 2^n, and the image representation may be tweaked too (eg converted to a palette/indexed format) as a strong hint to the encoder.

Overrides:

_reduceColoursQualityThreshold in class AbstractImageHandler