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From "Sebb (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SANSELAN-56) proposed enhancement reduces load time for some image files by 40 percent
Date Tue, 04 Oct 2011 20:44:34 GMT

    [ https://issues.apache.org/jira/browse/SANSELAN-56?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13120455#comment-13120455
] 

Sebb commented on SANSELAN-56:
------------------------------

The attachment ImagePrep.java dated 28/Sep/11 has "ASF granted license" = No, so we cannot
use it.
However, the same class is present in the patch dated 04/Oct/11 so perhaps the file is obsolete.

Either delete the file, or delete and re-attach with grant to ASF if it is still required.

The patch appears to contain more than just the loading speed fix. There is a change to BinaryFileFunctions.java
which appears to be a separate bug-fix.

There are also various spacing and other changes which make it quite hard to review the actual
changes.
It's a lot easier for committers if patches are restricted to the minimum required to implement
the change.

The package.html additions don't appear to be directly relevant, and the header ought to be
the standard AL header.
                
> proposed enhancement reduces load time for some image files by 40 percent
> -------------------------------------------------------------------------
>
>                 Key: SANSELAN-56
>                 URL: https://issues.apache.org/jira/browse/SANSELAN-56
>             Project: Commons Sanselan
>          Issue Type: Improvement
>         Environment: Tested in Windows, Linux, MacOS
>            Reporter: Gary Lucas
>              Labels: api-change
>         Attachments: ImagePrep.java, Sanselan-56-SpeedEnhanceTiff.patch
>
>   Original Estimate: 48h
>  Remaining Estimate: 48h
>
> I have identified an enhancement that reduces the time required to load TIFF image by
40 percent.  I have tested a modified version of Sanselan under Windows, Linux, and MacOS
with consistent savings on each platform.  Additionally, I suspect that this technique may
be applicable to other areas of the Sanselan code base, including more popular image formats
supported by Sanselan such as JPEG, PNG, etc.
> I propose to add the relevant code changes to the Sanselan code base.  Once these modifications
are in place, there would be an opportunity for others to look at the pro's and cons' of applying
the techniques to other data formats.
> The Enhancement
> To load an image from a TIFF file, Sanselan performs extensive data processing in order
to obtain RGB values for the pixels in the output image. The code for that processing appears
to be well written and efficient. Once the RGB value are obtained, they are stored in a Java
BufferedImage using a call  to the setRGB() method.
> Unfortunately, setRGB() is an extremely inefficient method.   A much, much better approach
is to store the data into an integer array and defer the creation of the buffered image until
all information for the image has been collected.    Java has a nice (though somewhat obscure)
API that lets memory in an integer array be transferred directly to a BufferedImage so that
the system does not have to allocate additional memory for this procedure (a very nice feature
when dealing with huge images).  This change virtually eliminated the overhead for transferring
data to images, which accounted for 40 percent of the time required to load images.  For TIFF
files, this was a reasonable approach because the TiffImageParser class always loads 4-byte
image  and the getGrayscaleBufferedImage() method is never used.  I have not investigated
the code for the other renders, but some refinement might be needed for the one-byte grayscale
images.
> Steps to Integration
> In sanselan.common, a new class called ImagePrep was created.  ImagePrep carries a width,
height, and an integer array for storing pixels.  It provides its own setRGB() method which
looks just like the one in BufferedImage.   Finally, it provides a method called getBufferedImage()
which creates a BufferedImage from its internal the integer array when the processing is complete.
> In the TiffImageParser classes, data is read from input stream and transferred to pixel
values in a series of classes known as PhotometricInterpreters.  These were modified to operate
on ImagePrep objects rather than BufferedImage objects.  The DataReader and TiffImageParser
classes were modified to pass ImagePrep objects into the photometric interpreters rather than
using BufferedImages.
> At the very last step, before passing its result back to the calling method (the Sanselan
main class, etc.), the TiffImageParser used the ImagePrep.getBufferedImage() to convert the
result to the expected form.

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