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From "Gary Lucas (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SANSELAN-56) proposed enhancement reduces load time for some image files by 40 percent
Date Sun, 26 Feb 2012 18:42:50 GMT

    [ https://issues.apache.org/jira/browse/SANSELAN-56?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13216806#comment-13216806
] 

Gary Lucas commented on SANSELAN-56:
------------------------------------

 

Hi Damjan,  

I'm not emotionally attached to most of my changes, and am willing to yield to your judgement
on most matters.    

The only one that I have any comment on is the issue about the 16 byte palette.  The issue
is whether Sanselan should include logic to handle a mistake in a data palette format.  The
question is how common is the mistake. I myself don't know. I've noticed that Microsoft Picture
and Fax viewer handles files that have the 8-byte palettes, but I have no insights into what
drove that particular design change.  

The only other thing I would disagree with is the characterization of my code changes as messy.
 Overreaching? Overly agressive? Reckless?  Okay.  But messy... say it ain't so :-)  

g.  




---
Gary W. Lucas, Senior Software Engineer
Sonalysts, Inc
215 Parkway North
Waterford, CT 06320
(860) 326-3682


                
> 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: 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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