Aliasing - Revision history

Erik Krause: /* Definition and Background */ linked to filters page

2008-10-06T17:20:21Z

‎Definition and Background: linked to filters page

Erik Krause: Prepared for new glossary template

2007-11-17T21:41:43Z

Prepared for new glossary template

WikiSysop: 6 revision(s)

2006-07-13T20:27:58Z

6 revision(s)

WikiSysop: 1 revision(s)

2006-07-13T19:56:38Z

1 revision(s)

Erik Krause: update: anti aliasing filters in PTools

2006-03-26T22:40:50Z

update: anti aliasing filters in PTools

Erik Krause: update: anti aliasing filters in PTools

2006-03-26T22:40:50Z

update: anti aliasing filters in PTools

New page

=== Definition and Background ===

'''''Aliasing''''' is a process that results in "jaggies" or Moire effects when an image is sampled or resampled.

The word "aliasing" comes from frequency-domain analysis. Slow periodic sampling of a signal causes high frequency components to be "aliased" into low frequency ones that corrupt the sampled signal.

To avoid aliasing, a signal must not contain frequencies that are higher than one half the sample rate. Likewise, an input image must not contain details that are smaller than one pixel in the output image.

This can be accomplished by appropriately filtering the signal or blurring the image before resampling it.

Such filtering is one way to '''''anti-alias'''''. <small>(There are others, not relevant here.)</small>

When using older versions of [[Panorama Tools]] (and derived tools such as [[PTStitcher]], [[nona]] or the [[Panorama Tools Plugins]]) the important thing to know was that Panorama Tools did not anti-alias until pano12 version 2.7.0.11. This meant that if you had Panorama Tools make a small panorama directly, it was likely to show jaggies or Moire effects.

In version 2.7.0.11 there where added a couple of anti-aliasing interpolators which can be used by either specifying the correct interpolator number in the [http://photocreations.ca/panotools/stitch.txt script]] or by choosing one of the interpolators directly if the Software supports it. However, the traditional interpolators "poly3", "spline16", "spline36", "sinc256", "spline64", "bilinear", "nearest neighbor" and "sinc1024" still cause aliasing.

=== Guidance ===

You will get better results by having Panorama Tools make a large panorama, then resizing it (downsampling) using some tool like [[Photoshop]], [[ImageMagick]] or the [[Gimp]] that does incorporate anti-aliasing, if you use a version prior to 2.7.0.11 or if it's not possible to use the new anti-aliasing filters.

=== Illustrations ===

The following images illustrate this guidance. They show crops from a 1000x500 panorama.

On the left is what Photoshop produced by downsampling from a 6068x3034 pano, using the Image Size command with Bicubic resampling. (6068x3034 was the [[PTGui]] "optimum" size.)

On the right is what Panorama Tools produced directly at 1000x500.

'''Actual pixels'''

[[Image:AliasingPScubic.jpg]] [[Image:AliasingPTpoly3.jpg]]

'''2X enlargement to show the aliasing more clearly'''

[[Image:AliasingPScubic_2x.jpg]] [[Image:AliasingPTpoly3_2x.jpg]]
[[Category:Glossary]]

Bruno: categorised

2005-11-11T12:10:54Z

categorised

Bruno: linkified

2005-07-21T15:33:28Z

linkified

Rjlittlefield: reformatting and wordsmithing

2005-06-26T18:14:49Z

reformatting and wordsmithing

Rjlittlefield: main content added

2005-06-26T18:05:32Z

main content added

← Older revision		Revision as of 21:41, 17 November 2007
Line 1:		Line 1:
		+	{{Glossary\|less than optimal resampling that causes "jaggies" and Moire effects.}}
	=== Definition and Background ===		=== Definition and Background ===

← Older revision		Revision as of 12:10, 11 November 2005
Line 33:		Line 33:

	[[Image:AliasingPScubic_2x.jpg]] [[Image:AliasingPTpoly3_2x.jpg]]		[[Image:AliasingPScubic_2x.jpg]] [[Image:AliasingPTpoly3_2x.jpg]]
		+	[[Category:Glossary]]

@@ Line 11: / Line 11: @@
 Such filtering is one way to '''''anti-alias'''''.  <small>(There are others, not relevant here.)</small>
-When using Panorama Tools, the important thing to know is that Panorama Tools does not anti-alias.  This means that if you have Panorama Tools make a small panorama directly, it is likely to show jaggies or Moire effects.
+When using [[Panorama Tools]] (and derived tools such as [[PTStitcher]], [[nona]] or the [[Panorama Tools Plugins]]) the important thing to know is that Panorama Tools does not anti-alias.  This means that if you have Panorama Tools make a small panorama directly, it is likely to show jaggies or Moire effects.
 === Guidance ===
-You will get better results by having Panorama Tools make a large panorama, then resizing it (downsampling) using some tool like Photoshop that does incorporate anti-aliasing.
+You will get better results by having Panorama Tools make a large panorama, then resizing it (downsampling) using some tool like [[Photoshop]], [[ImageMagick]] or the [[Gimp]] that does incorporate anti-aliasing.
 === Illustrations ===
@@ Line 21: / Line 21: @@
 The following images illustrate this guidance.  They show crops from a 1000x500 panorama.
-On the left is what Photoshop produced by downsampling from a 6068x3034 pano, using the Image Size command with Bicubic resampling.  (6068x3034 was the PTGui "optimum" size.)
+On the left is what Photoshop produced by downsampling from a 6068x3034 pano, using the Image Size command with Bicubic resampling.  (6068x3034 was the [[PTGui]] "optimum" size.)
 On the right is what Panorama Tools produced directly at 1000x500.

@@ Line 1: / Line 1: @@
-'''Aliasing''' is a process that results in "jaggies" or Moire effects when an image is sampled or resampled.
+=== Definition and Background ===
 The word "aliasing" comes from frequency-domain analysis.  Slow periodic sampling of a signal causes high frequency components to be "aliased" into low frequency ones that corrupt the sampled signal.
@@ Line 7: / Line 9: @@
 This can be accomplished by appropriately filtering the signal or blurring the image before resampling it.
-Such filtering is one way to '''anti-alias'''.  <small>(There are others, not relevant here.)</small>
+Such filtering is one way to '''''anti-alias'''''.  <small>(There are others, not relevant here.)</small>
 When using Panorama Tools, the important thing to know is that Panorama Tools does not anti-alias.  This means that if you have Panorama Tools make a small panorama directly, it is likely to show jaggies or Moire effects.
 You will get better results by having Panorama Tools make a large panorama, then resizing it (downsampling) using some tool like Photoshop that does incorporate anti-aliasing.
-The following images illustrate this guidance.  They show crops from a 1000x500 panorama.  On the left is what Photoshop produced by downsampling from a 6068x3034 pano.  On the right is what Panorama Tools produced directly at 1000x500.
+=== Illustrations ===
-"Actual pixels"
+The following images illustrate this guidance.  They show crops from a 1000x500 panorama.
 [[Image:AliasingPScubic.jpg]] [[Image:AliasingPTpoly3.jpg]]
-X enlargement to show the aliasing more clearly.
 [[Image:AliasingPScubic_2x.jpg]] [[Image:AliasingPTpoly3_2x.jpg]]

← Older revision		Revision as of 18:05, 26 June 2005
Line 1:		Line 1:
−	(~~Page under construction~~)	+	'''Aliasing''' is a process that results in "jaggies" or Moire effects when an image is sampled or resampled.
		+
		+	The word "aliasing" comes from frequency-domain analysis. Slow periodic sampling of a signal causes high frequency components to be "aliased" into low frequency ones that corrupt the sampled signal.
		+
		+	To avoid aliasing, a signal must not contain frequencies that are higher than one half the sample rate. Likewise, an input image must not contain details that are smaller than one pixel in the output image.
		+
		+	This can be accomplished by appropriately filtering the signal or blurring the image before resampling it.
		+
		+	Such filtering is one way to '''anti-alias'''. <small>(There are others, not relevant here.)</small>
		+
		+	When using Panorama Tools, the important thing to know is that Panorama Tools does not anti-alias. This means that if you have Panorama Tools make a small panorama directly, it is likely to show jaggies or Moire effects.
		+
		+	You will get better results by having Panorama Tools make a large panorama, then resizing it (downsampling) using some tool like Photoshop that does incorporate anti-aliasing.
		+
		+	The following images illustrate this guidance. They show crops from a 1000x500 panorama. On the left is what Photoshop produced by downsampling from a 6068x3034 pano. On the right is what Panorama Tools produced directly at 1000x500.
		+
		+	"Actual pixels"
		+
		+	[[Image:AliasingPScubic.jpg]] [[Image:AliasingPTpoly3.jpg]]
		+
		+	2X enlargement to show the aliasing more clearly.
		+
		+	[[Image:AliasingPScubic_2x.jpg]] [[Image:AliasingPTpoly3_2x.jpg]]

@@ Line 14: / Line 14: @@
 When using older versions of [[Panorama Tools]] (and derived tools such as [[PTStitcher]], [[nona]] or the [[Panorama Tools Plugins]]) the important thing to know was that Panorama Tools did not anti-alias until pano12 version 2.7.0.11.  This meant that if you had Panorama Tools make a small panorama directly, it was likely to show jaggies or Moire effects.
-In version 2.7.0.11 there where added a couple of anti-aliasing interpolators which can be used by either specifying the correct interpolator number in the [http://photocreations.ca/panotools/stitch.txt script]] or by choosing one of the interpolators directly if the Software supports it. However, the traditional interpolators "poly3", "spline16", "spline36", "sinc256", "spline64", "bilinear", "nearest neighbor" and "sinc1024" still cause aliasing.
+In version 2.7.0.11 a couple of [[anti-aliasing interpolators]] where added which can be used by either specifying the correct interpolator number in the [http://photocreations.ca/panotools/stitch.txt script]] or by choosing one of the interpolators directly if the Software supports it. However, the traditional interpolators "poly3", "spline16", "spline36", "sinc256", "spline64", "bilinear", "nearest neighbor" and "sinc1024" still cause aliasing.
 === Guidance ===

← Older revision	Revision as of 20:27, 13 July 2006
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