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New Image Decompression Manager APIs

This section discusses new Image Decompression Manager APIs introduced in QuickTime 6.

QTGetPixelFormatDepthForImageDescription

Returns the corresponding depth value that should be used in image descriptions.

short QTGetPixelFormatDepthForImageDescription (OSType PixelFormat);

Discussion

Given a pixel format, this function returns the corresponding depth value that should be used in image descriptions. Such a value is not the literal number of bits per pixel, but the closest corresponding classic QuickDraw depth:

• for any pixel format with an alpha channel, 32

• for grayscale pixel formats of 8 or more bits per pixel, 40

• for color quantized to 5 or 6 bits per component, 16

• for all other color pixel formats, 24

Availability

• Available in Mac OS X v10.2 and later.

Declared In

ImageCompression.h

GraphicsImportSetImageIndexToThumbnail

Looks for a subimage that contains a thumbnail.

ComponentResult GraphicsImportSetImageIndexToThumbnail
(GraphicsImportComponent ci);

Discussion

This routine looks for a subimage that contains a thumbnail. If the function finds one, it sets the image index to that subimage. If the function does not find one, it returns noThumbnailFoundErr.

The base graphics importer’s implementation of SetImageIndexToThumbnail works by looking for the first image index that returns a kQTIndexedImageType metadata item containing the kQTIndexedImageIsThumbnail tag. Format-specific graphics importers may override this with more efficient algorithms.

Availability

• Available in Mac OS X v10.2 and later.

Declared In

ImageCompression.h

ImageCodecMergeFloatingImageOntoWindow

Draws the current contents of a floating image.

ComponentResult ImageCodecMergeFloatingImageOntoWindow(
ComponentInstance ci,
UInt32 flags );

Discussion

Some hardware acceleration transfer codecs create a “floating image” in front of the window; when this is deactivated or hidden, whatever was previously drawn in that section of the window reappears. Such transfer codecs should implement the MergeFloatingImageOntoWindow call, which draws the current contents of the floating image onto the window below, so that the floating image may be deactivated or hidden without the image changing.

Availability

• Available in Mac OS X v10.2 and later.

Declared In

ImageCodec.h

ImageCodecRemoveFloatingImage

Hides the floating image without having to close the component.

ComponentResult ImageCodecRemoveFloatingImage(
ComponentInstance ci,
UInt32 flags );

Availability

• Available in Mac OS X v10.2 and later.

Declared In

ImageCodec.h

Some hardware acceleration transfer codecs create a “floating image” in front of the window; when this is deactivated or hidden, whatever was previously drawn in that section of the window reappears. Such transfer codecs should implement the RemoveFloatingImage call, so that the Image Compression Manager can ask it to hide the floating image without having to close the component.

The floating image should be shown again on the next call to DrawBand.

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