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The JPEG algorithm attempts to compress images in such a way that storage requirements
are minimized while keeping the image perceptually undistorted as much as possible. This
is accomplished by finding regions in the image that have a low amount of detail and
lumping those pixels into 16 x 16 square pixel blocks that will have the same color
information. Because the human eye is far more sensitive to changes in luminance than in
color (chrominance), JPEG uses much more compression for chrominance values than for
luminance. This optimizes the compression with minimal visible degradation.
We should try to avoid using JPEG compressed files to enhance, and create them only as
an output file permutation for e-mail or WEB, however sometimes they are the only
existing version to work with.
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Figure 1. Original Texas longhorn image
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Figure 1 shows a digital photograph saved as a JPEG file. By simple observation it is
difficult to notice any JPEG blocks within the image, even though they are there. So
far so good.
The problem of JPEG blocks manifests itself when we attempt to manipulate the color
information with some sort of filter or operation. Let's just say that we want to make
the image more vivid by increasing saturation and luminance where they are lacking.
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Figure 2. After a gain on saturation and value using Asiva
Shift+Gain plug-in.
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Figure 2 shows the result of a gain in the HSV color space, in which saturation was
increased by 60% and value was increased by 30% using the Asiva Shift+Gain plug-in.
The colors in Figure 2 are much more vivid, but there is a serious problem with the
results. Now you can easily spot the JPEG blocks, particularity in the sky.
That's where the Asiva JPEG Deblocker plug-in comes in. It smooths out the JPEG blocks
while keeping the detail in the image practically unaltered.
Important Note: You are going to have to either step backwards
in your Photoshop History, or close the source JPEG image without saving and reopen it,
because you DO NOT want to alter the source JPEG image in any way before Deblocking it
with Asiva.
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Figure 3. After running the Asiva JPEG Deblocker plug-in.
Note you cannot really see any difference.
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Figure 3 is the result of running the Asiva JPEG Deblocker plug-in
on the original image. Notice that Figure 3 and Figure 1 are virtually identical and
you will not be able to necessarily tell that the plug-in did anything until you perform
another filter or operation.
Applying the very same gain to the Asiva JPEG deblocked image results in Figure 4.
The square blocks are largely gone and smoothed-out, without destroying the detail in
the image.
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Figure 4. Indentical Gain on the Asiva JPEG deblocked source
image.
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Mac:
- PPC Mac, OS 9.2.2 through Mac OS X 10.4.8
- Adobe Photoshop 5.5 and higher
PC:
- Microsoft Windows 2000 or XP
- Adobe Photoshop 5.5 and higher
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- Download Asiva JPEG Deblocker Quickstart Tutorial Mac PC
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