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#51
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What program is best at JPEG compression?
"HEMI-Powered" wrote in message
... CSM1 added these comments in the current discussion du jour ... But, I AM interested in this thread because I DO want to learn. New knowledge is always being created and to ignore it is to be both stupid and ignorant. The best way to handle a lot of photo editing is to convert the original Jpeg image from the camera (if that is what you camera produces) to a lossless format such as TIFF. Tiff can be compressed using LZW compression, which is the same compression scheme as ZIP files. LZW does not compress as much as JPEG, but the compression is 100% no loss. As you probably know, my Rebel XT can do JPEG or RAW or both, but not TIFF. I understand your point, of course, but about Ivory Soap Pure percent of the time, I can get there with just one save. When I cannot, I will save the file as a pspimage file so as to preserve layers and Alpha channel stuff. I do some of the former but a LOT of the latter to store various kinds of selections so I do not have to always do global edits when working on color, brightness/contrast, noise, etc. You can convert RAW to Tiff in ZoomBrowser EX that was included with your Canon Rebel XT. From the EOS DIGITAL Software Instruction Manual Windows (PDF, 3.98 MB). The Supported Images are JPEG, RAW, BMP, TIFF and PCD (Kodak Photo CD images). But I was talking about converting the Jpeg image in a Photo editor(Photoshop or The Gimp) to a Tiff image, before doing any edits. By the way, Tiff does support EXIF info. Tiff is one of the image formats in the EXIF 2.2 specification. The metadata part of a EXIF Jpeg are TIF tags. You load the jpeg, and immediately Save As Tiff. You then work on the Tiff image only, you leave the jpeg as the master image. Tiff LZW supports EXIF also, the only difference is a smaller file in most cases, however there are cases where the Tiff LZW file is actually larger than the uncompressed TIFF. After converting to TIFF, you can edit and save as many times as you wish, with no loss in picture quality. After you are done with editing, you can then save a final image as Jpeg. You should only do very limited edits on a JPEG file. Every time you save a JPEG you are re-compressing and losing information. I know you're replying to the whole NG, but this doesn't happen to me, although I do understand the non-linear degradation that begins at about the 2nd re-edit/re-save cycle. There are claims of lossless JPEG, but not very many photo editors are supporting the lossless formats. And they are not common. Lossless is supported by so few apps and not at all on the web and Usenet that it is useless. As you suggest, TIFF is better but has the disadvantage that EXIF cannot be saved if you do LZW compression, which makes them pretty large. So, again, when I need to, I use pspimage because it saves EVERYTHING I am doing, same as PhotoShop proprietary files do and any other good app can do. Jpeg and Tiff image formats have been around for years and are not likely to go away. As I understand it, JPEG began with a committee or consortia of about half mathemticians and half real photographers to develop a new format that could vastly reduce file size beyond the approx. 50% of an LZW TIFF. I haven't read the spec in a long time, but I vaguely remember that the definition for JPEG=1 out of a possible 100 was to approximate LZW TIFF. And, since photographers are only interested in continous tone (to the extent that is true for 24-bit color) photos, and they were NOT interested in line art or raster text, both of which take an awful beating by JPEG unless you are extremely conservative in your settings. At least, that has been my experience and what I have heard/seen others say is true. Here is a good list of image file formats and the best use. http://www.scantips.com/basics09.html Continue reading the following pages. A lot of good information in those pages Thanks muchly! -- HP, aka Jerry -- CSM1 http://www.carlmcmillan.com -- |
#52
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What program is best at JPEG compression?
CSM1 added these comments in the current discussion du jour ...
As you probably know, my Rebel XT can do JPEG or RAW or both, but not TIFF. I understand your point, of course, but about Ivory Soap Pure percent of the time, I can get there with just one save. When I cannot, I will save the file as a pspimage file so as to preserve layers and Alpha channel stuff. I do some of the former but a LOT of the latter to store various kinds of selections so I do not have to always do global edits when working on color, brightness/contrast, noise, etc. You can convert RAW to Tiff in ZoomBrowser EX that was included with your Canon Rebel XT. Assuming that the best quality of JPEG is Okey, Dokey, I could convert that to TIFF if I were of a mind to convert it to any lossless format, which I am not. I don't do RAW yet because despite more than a year of looking, I have year to find a "RAW for Dummies" book that can get me to the first step in the learning process. One time. I am interested in all of this, but until I hear of a truly better mousetrap, my current workflow works just fine, with a rare need to save in pspimage, From the EOS DIGITAL Software Instruction Manual Windows (PDF, 3.98 MB). The Supported Images are JPEG, RAW, BMP, TIFF and PCD (Kodak Photo CD images). I also have Raw Shooter Premium, but do not have the need yet, considering the above - don't know how to get to the starting line for RAW, and don't really want to shoot at 8 mega pixels when I save to about 1.5 MP eventually. But I was talking about converting the Jpeg image in a Photo editor(Photoshop or The Gimp) to a Tiff image, before doing any edits. By the way, Tiff does support EXIF info. Tiff is one of the image formats in the EXIF 2.2 specification. The metadata part of a EXIF Jpeg are TIF tags. I thought that to get EXIT into TIFF, it has to be the uncompressed kind. You load the jpeg, and immediately Save As Tiff. You then work on the Tiff image only, you leave the jpeg as the master image. Tiff LZW supports EXIF also, the only difference is a smaller file in most cases, however there are cases where the Tiff LZW file is actually larger than the uncompressed TIFF. I'll look again, maybe I am harboring a misconception. Thanks. -- HP, aka Jerry |
#53
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What program is best at JPEG compression?
Bill Tuthill added these comments in the current discussion du
jour ... What's the difference between PSP's 2x1 1x1 1x1 and PSP's 1x2 1x1 1x1 encoding? I used the former, not the latter. PSP also has a bunch of weird encodings not encountered in other software. My experience with PSP 8 some time ago and 9 more recently is that 1x2 creates larger files but higher quality due to less artifacts of various types, one insidious one looking for all the world like noise but it isn't. 2x2, OTOH, produces a much smaller file size; you need to visually judge the difference in quality to see which you like better. I only use 2x2 when I am desperate for smaller size and upping the JPEG compression number is also producing unacceptable defects. It is a big juggling act and some experimentation may be necessary for you. -- HP, aka Jerry |
#54
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What program is best at JPEG compression?
HEMI-Powered wrote:
heavily edited, for brevity I keep in mind that the "P" in JPEG means "Photographer". heavily edited Hello, Jerry: JPEG stands for "Joint Photographic Experts Group" -- just being a stickler, dog. ;-) Cordially, John Turco |
#55
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What program is best at JPEG compression?
John Turco added these comments in the current discussion du
jour ... HEMI-Powered wrote: heavily edited, for brevity I keep in mind that the "P" in JPEG means "Photographer". heavily edited Hello, Jerry: JPEG stands for "Joint Photographic Experts Group" -- just being a stickler, dog. ;-) same thing, I said it's been a long time, but P for Photographer is close enough for P = Photographic to make the point I was making, OK by you? thank you. -- HP, aka Jerry |
#56
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What program is best at JPEG compression?
On Jul 27, 2:53 pm, "HEMI-Powered" wrote:
Martin Brown added these comments in the current discussion du jour ... Bill, I don't want to hit this at all hard, but I could swear that during the beta test for PSP 8, Jasc's Chief Scientist, the same guy, Kris Zaklika, that wrote the math for DCNR, said that PSP 8 could decide in a "smart" way which block size to use. I could be Either way that statement is incredibily funny. Why is that "incredibly funny", Martin? I get the feeling that you are calling me a fool. No. But I am laughing at the claim that PSPro v8 could decide in a "smart" way which block size to use when it had one of the most broken JPEG implementations ever seen in a commercial released product. PSP 8 has a demonstrably very broken chroma subsampling implementation in its JPEG codec. It is a testament to just how robust JPEG is that more people have not noticed this flaw. Come again? I do not know either the math or the implementation but NEVER had any major problems with PSP 8 during the years from its release until PSP 9 was released, You were unaware of the problem. So perhaps you don't consider colour errors a problem. Or you never use chroma subsampling AFAIK the not subsampled 1x1 1x1 1x1 variant works OK in PSPro 8. NB Photoshop defaults to not subsampled for the top half of its highest quality settings and for some images there is a big step in quality there. The simplest line art test to show its failings on chroma encoding is to encode a pure red and pure blue 16x16 pokerdot test pattern in each of the possible phases save as JPEG default 2x2 subsampled at maximum quality and then reload it. Half of the newly decoded image not even a vaguely satisfactory approximation to the original (with gross residual colour errors - completely the wrong colour bright red instead of purple). 2x1 subsampling gets an even more incorrect result with alternating blue and red stripes in addition. I don't do line art, don't do vectors, don't do text, don't do layers, I ONLY do raster graphics bitmap photo/scan editing. So, pathological examples such as ANY JPEG implementation mangling line art or text does not surprise me, as that is hardly what it's authors had in mind. I keep in mind that the "P" in JPEG means "Photographer". So, I will hardly dispute your conclusions but do not see how that is relevant to JPEG's real purpose and usage, other than line art people also want mimimal size images as well. But, I would think that to maintain maximum quality, you would want to use a lossless format or even save only to your favorite editors proprietary format, e.g., pspsimage. The line art example is constructed to demonstrate a specific implementation fault in the starkest possible form. However, the problem is still present in every colour JPEG image made with chroma subsampling. The damage is less, but there is still unwarranted and irrecoverable damage to the stored JPEG image coefficients. Incidentally for some line art JPEG at highest quality not subsampled can sometimes be the smallest file size. JPEG was designed for photographic images, but it is quite capable of storing line art with the right settings (although usually PNG or GIF will be more compact). For my car pictures, 2x2 subsampling turns them into one big artifact, I never touch the stuff, so never suffer from its limitions or damage. Chroma subsampling tends to hit sharp red or blue colour transitions disproportionately. And they are rather common colours for cars. But unless you zoom in to pixel level it should be virtually invisible. Some of the damage you are seeing could well be from a flawed JPEG implementation. Check that the problem persists with IrfanView or GIMP. Regards, Martin Brown |
#57
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What program is best at JPEG compression?
On Jul 28, 12:02 am, Bill Tuthill wrote:
In rec.photo.digital Martin Brown wrote: PSP 8 has a demonstrably very broken chroma subsampling implementation in its JPEG codec. It is a testament to just how robust JPEG is that more people have not noticed this flaw. Thanks for your excellent explanation of the issue. The simplest line art test to show its failings on chroma encoding is to encode a pure red and pure blue 16x16 pokerdot test pattern in each of the possible phases save as JPEG default 2x2 subsampled at maximum quality and then reload it. Half of the newly decoded image not even a vaguely satisfactory approximation to the original (with gross residual colour errors - completely the wrong colour bright red instead of purple). 2x1 subsampling gets an even more incorrect result with alternating blue and red stripes in addition. Is 2x1 same as 4:2:2? I thought the ImageMagick -sampling_factor option only accepted 1x1 and 2x2, but it does accept 2x1 and produces what looks (to jpegdump) similar to 4:2:2 chroma subsampling from digital cameras. 2x1 is typically the encoding used by digicams. 1x2 sampling was unknown until the lossless JPEG transcoder allowed images to be rotated in the coefficient space. Some decoders don't decode 1x2 chroma especially well. In principle at least a digicam could encode a Bayer mask sampled image in a more compact form with 2Y, 1Cr, 1Cb for every 4 sensor pixels, but the standard had no way of anticipating this development in all digital imaging sowe are stuck with 4:2:2 where half the pixels being stored are redundant. The original is online athttp://www.nezumi.demon.co.uk/photo/jpeg/rb_1x1.jpg Correct IJG JPEG encodinghttp://www.nezumi.demon.co.uk/photo/jpeg/rb_2x2.jpg I think you got that filename wrong. Yes. Should be http://www.nezumi.demon.co.uk/photo/jpeg/rb_2x2_ijg.jpg And the mess that PSP 8 makes of it at http://www.nezumi.demon.co.uk/photo/jpeg/rb_2x1.jpg http://www.nezumi.demon.co.uk/photo/jpeg/rb_2x2.jpg I would be curious to know if this defect was fixed in later versions. It appears to be mostly fixed. I'm not certain that the colors are as accurate as with the equivalent IJG encodings, but they certainly don't display the wild inaccuracy of the above encodings. I put them online for you to see: http://cacreeks.com/psp/ (filenames hopefully self-explanatory) There seems to be a slight residual systematic error, but it is close enough now for all practical purposes. What's the difference between PSP's 2x1 1x1 1x1 and PSP's 1x2 1x1 1x1 encoding? I used the former, not the latter. PSP also has a bunch of weird encodings not encountered in other software. One averages the chroma in pairs horizontally and the other vertically. Empirically it was found that for the standard 4:3 and 3:2 aspect ratios of cameras 2x1 subsampling results in a more compact representation. The same empiricism explains why the default quantisation matrix in the standard is not symmetrical. I wouldn't like to comment on the weird subsampling options offered in PSPro except to say they may not do what they say on the tin. The ones in PSPro 8 certainly do not. Regards, Martin Brown |
#58
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What program is best at JPEG compression?
Martin Brown added these comments in the current discussion du
jour ... Martin, I am top-posting only because I wanted to answer everything easily at one time. For MY work - just my work, not saying anything about anyone elses - PSP 8 worked fine, and PSP 9 works better. I never had color/chroma problems with 8, don't with 9. Never had excessive artifacts with either that I didn't create by blundering to too much compression. Jasc may have made junk software for many, but it worked fine for me. It is OK that we disagree, if everyone agreed all the time, a dull world it would be. Just for the records, what do you use now? I assume it is NOT PSP X or XI as I have heard nothing but bad comments about them since Corel took over. Have a great week in spite of any friendly controversy. No harm, no foul. On Jul 27, 2:53 pm, "HEMI-Powered" wrote: Martin Brown added these comments in the current discussion du jour ... Bill, I don't want to hit this at all hard, but I could swear that during the beta test for PSP 8, Jasc's Chief Scientist, the same guy, Kris Zaklika, that wrote the math for DCNR, said that PSP 8 could decide in a "smart" way which block size to use. I could be Either way that statement is incredibily funny. Why is that "incredibly funny", Martin? I get the feeling that you are calling me a fool. No. But I am laughing at the claim that PSPro v8 could decide in a "smart" way which block size to use when it had one of the most broken JPEG implementations ever seen in a commercial released product. PSP 8 has a demonstrably very broken chroma subsampling implementation in its JPEG codec. It is a testament to just how robust JPEG is that more people have not noticed this flaw. Come again? I do not know either the math or the implementation but NEVER had any major problems with PSP 8 during the years from its release until PSP 9 was released, You were unaware of the problem. So perhaps you don't consider colour errors a problem. Or you never use chroma subsampling AFAIK the not subsampled 1x1 1x1 1x1 variant works OK in PSPro 8. NB Photoshop defaults to not subsampled for the top half of its highest quality settings and for some images there is a big step in quality there. The simplest line art test to show its failings on chroma encoding is to encode a pure red and pure blue 16x16 pokerdot test pattern in each of the possible phases save as JPEG default 2x2 subsampled at maximum quality and then reload it. Half of the newly decoded image not even a vaguely satisfactory approximation to the original (with gross residual colour errors - completely the wrong colour bright red instead of purple). 2x1 subsampling gets an even more incorrect result with alternating blue and red stripes in addition. I don't do line art, don't do vectors, don't do text, don't do layers, I ONLY do raster graphics bitmap photo/scan editing. So, pathological examples such as ANY JPEG implementation mangling line art or text does not surprise me, as that is hardly what it's authors had in mind. I keep in mind that the "P" in JPEG means "Photographer". So, I will hardly dispute your conclusions but do not see how that is relevant to JPEG's real purpose and usage, other than line art people also want mimimal size images as well. But, I would think that to maintain maximum quality, you would want to use a lossless format or even save only to your favorite editors proprietary format, e.g., pspsimage. The line art example is constructed to demonstrate a specific implementation fault in the starkest possible form. However, the problem is still present in every colour JPEG image made with chroma subsampling. The damage is less, but there is still unwarranted and irrecoverable damage to the stored JPEG image coefficients. Incidentally for some line art JPEG at highest quality not subsampled can sometimes be the smallest file size. JPEG was designed for photographic images, but it is quite capable of storing line art with the right settings (although usually PNG or GIF will be more compact). For my car pictures, 2x2 subsampling turns them into one big artifact, I never touch the stuff, so never suffer from its limitions or damage. Chroma subsampling tends to hit sharp red or blue colour transitions disproportionately. And they are rather common colours for cars. But unless you zoom in to pixel level it should be virtually invisible. Some of the damage you are seeing could well be from a flawed JPEG implementation. Check that the problem persists with IrfanView or GIMP. Regards, Martin Brown -- HP, aka Jerry |
#59
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What program is best at JPEG compression?
Martin Brown added these comments in the current discussion du
jour ... On Jul 28, 12:02 am, Bill Tuthill wrote: In rec.photo.digital Martin Brown wrote: PSP 8 has a demonstrably very broken chroma subsampling implementation in its JPEG codec. It is a testament to just how robust JPEG is that more people have not noticed this flaw. Thanks for your excellent explanation of the issue. The simplest line art test to show its failings on chroma encoding is to encode a pure red and pure blue 16x16 pokerdot test pattern in each of the possible phases save as JPEG default 2x2 subsampled at maximum quality and then reload it. Half of the newly decoded image not even a vaguely satisfactory approximation to the original (with gross residual colour errors - completely the wrong colour bright red instead of purple). 2x1 subsampling gets an even more incorrect result with alternating blue and red stripes in addition. Is 2x1 same as 4:2:2? I thought the ImageMagick -sampling_factor option only accepted 1x1 and 2x2, but it does accept 2x1 and produces what looks (to jpegdump) similar to 4:2:2 chroma subsampling from digital cameras. 2x1 is typically the encoding used by digicams. 1x2 sampling was unknown until the lossless JPEG transcoder allowed images to be rotated in the coefficient space. Some decoders don't decode 1x2 chroma especially well. I can neither confirm nor deny your assertation here, none of my digitals tell me what they use. I generally do NOT use 2x2 because I find it produces too many artifacts and there is too much of a tendency for color shifting. My two preferences at 1x2 or 1x1, both of which work fine for my car picturs. In principle at least a digicam could encode a Bayer mask sampled image in a more compact form with 2Y, 1Cr, 1Cb for every 4 sensor pixels, but the standard had no way of anticipating this development in all digital imaging sowe are stuck with 4:2:2 where half the pixels being stored are redundant. The original is online athttp://www.nezumi.demon.co.uk/photo/jpeg/rb_1x1.jpg Correct IJG JPEG encodinghttp://www.nezumi.demon.co.uk/photo/jpeg/rb_2x2.jpg I think you got that filename wrong. Yes. Should be http://www.nezumi.demon.co.uk/photo/jpeg/rb_2x2_ijg.jpg And the mess that PSP 8 makes of it at http://www.nezumi.demon.co.uk/photo/jpeg/rb_2x1.jpg http://www.nezumi.demon.co.uk/photo/jpeg/rb_2x2.jpg I would be curious to know if this defect was fixed in later versions. It appears to be mostly fixed. I'm not certain that the colors are as accurate as with the equivalent IJG encodings, but they certainly don't display the wild inaccuracy of the above encodings. I put them online for you to see: http://cacreeks.com/psp/ (filenames hopefully self-explanatory) There seems to be a slight residual systematic error, but it is close enough now for all practical purposes. What's the difference between PSP's 2x1 1x1 1x1 and PSP's 1x2 1x1 1x1 encoding? I used the former, not the latter. PSP also has a bunch of weird encodings not encountered in other software. One averages the chroma in pairs horizontally and the other vertically. Empirically it was found that for the standard 4:3 and 3:2 aspect ratios of cameras 2x1 subsampling results in a more compact representation. The same empiricism explains why the default quantisation matrix in the standard is not symmetrical. I wouldn't like to comment on the weird subsampling options offered in PSPro except to say they may not do what they say on the tin. The ones in PSPro 8 certainly do not. Regards, Martin Brown I have learned a lot about the math and science behind these "strange" number strings. Thank you for taking the time to educate a long-standing PSP user who is still (apparantly) a relative newbie. -- HP, aka Jerry |
#60
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What program is best at JPEG compression?
On Jul 27, 2:45 pm, "HEMI-Powered" wrote:
Martin Brown added these comments in the current discussion du jour ... It's not really lossless, because most images are not evenly divisible by 8 in both directions, so "lossless" rotation usually trims off some pixels rows or columns on the bottom or right side. A good implementation of true lossless rotation refuses point blank to do it if the requirements for preserving all the original information are not met. For a crop it is that the top left corner must start on a block boundary. Unless you are eagle eyed and have fine detail crossing the edge at an oblique angle you are unlikely to spot this happening casually - a lossless crop need not be a multiple of 8 in dimension as the bottom right corner is unrestricted. The problem is due to a weakness in the original JPEG spec which never envisaged that programs would crop or rotate images in raw coefficient space. It could be almost trivially fixed by adding a top and left crop offset TAG (2 bytes) to the existing spec and increasing the size of the image to the next higher multiple of 8/16. How big of a problem is lossy compression vs. lossles-but-with- severe limitations, anyway? The limitations are no longer all that severe. And they could be removed entirely if the standards committee decided that it was worthwhile changing the spec to accomodate recent developments. Sure, I've mangled a few by over re- editing my JPEGs when I had no choice, and I've damaged a few visibly but not catasttrophically, but by doing the re-save judiciously and by using careful softening of the aliasing and artifacts that may result, I've always been able to get by. Oh yes. An image good enough for all practical purposes should be the target. I am generally interested in finding the smallest image of adequate quality to be fit for purpose for a given source image. In this respect wizards that let you compare critical parts of an image at different compression settings and see the effects in real time are excellent. And programs that just rename the original image buffer but leave the original image on display are insidious and dangerous. Too many people end up overcompressing orginal images by accident. don't think I have low standards of quality, but then, I am also not a purist, theotician, nor extremist. I suppose I count myself as a pragmatic purist with an interest in the mathematics. Given the number of digital cameras about these days I would hazard a guess that most original source JPEG images are multiples of 8 in both dimensions (and that a substantial number are now multiples of 256). Since my first digital in early 2001, I have immedidately tested the two or more "quality" or "compression" options available and always come the conclusion that "standard" or "normal" produces visible artifacts in a high enough percenteage, maybe 5%, maybe 10%+, I always select "fine", "quality", whichever is the least compression since I do not use RAW so of necessity I will be doing at least one edit and one re-save. That philsophy has been quite successful for me in my type of photography and for my standards of quality and excellence. The highest quality in camera JPEG setting is always worthwhile for maximum flexibility. The only time I ever go down a step has been when I was in danger of running out of media a long way from any shops. If it is a choice between slightly inferior images or no images after running out of media then it is a useful tradeoff in extremis. You can't do anything similar with film - either you have an unexposed roll or you don't - there is no option to take twice as many smaller shots. Digicams situation is slightly complicated by the default 2x1 chroma subsampling. This means that although lossless rotation is exact and truly lossless some applications will display a slightly different image from the rotated coefficients. So for example: I have no clue what my Canon Rebel XT uses, but is seems unlikely that it is 2x1 as I have found that to be a fairly damaging setting. I don't know, but would think they use either 1x1 (none) or no more than 1x2. 2x1 is the default for almost all digicams (and it is for the fine sample rebel XT image on DPreview). The Bayer filter mask makes it non- sensical to use anything higher. You haven't measured the R or B data with sufficient spatial resolution to merit anything more. Only Foveon sensors or scanners sampling RGB at every pixel can justify a 1x1 subsampling. 2x1 should not normally be that damaging unless the source image is line art with significant pixel wide blue and red stripes. 1x2 was rarely encountered until the JPEG transcoder allowed images to be rotated in coefficient space. They are the notation for 2 chroma pixels average together horizontally or vertically. Regards, Martin Brown |
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