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#31
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What program is best at JPEG compression?
Bill Tuthill added these comments in the current discussion du
jour ... Until I started reading posts in this thread, I was unaware that there are ANY programs that can alter a JPEG without having to recompress the entire image. I can see your point about a localized change like the small parts of an image that had red eye removed, but I would think that you are right that any change that affects literally every pixel in the image, which would happen in your example of changing colors, would require a So I guess you know that Irfanview, among other applications, can do lossless rotation and flip, although it truncates to 8-pixel boundaries so it's only truly lossless with 8x pixel dimensions. All good apps can do lossless rotation, in 90 degree increments. If Irfanview can do an arbitrary rotation losslessly, I'm not aware of it, Bill. Which did you mean? PSP 9 can also do a lossless rotation, but I rarely use it because I've never been able to see any difference between lossless and ordinary 90 deg rotates. But, in my quote above, I concurred with another person that a global color change would alter the entire bitmap requiring a full recompress. To guess JPEG parameters, you can obtain the "jpegdump" program by Allan N. Hessenflow. When saving an edited JPEG, the destruction is minimal if you save with the same quality and chroma subsampling. Thanks for the heads up. Over some 13 or 14 years of JPEG experience, I have adopted my own norms for best first guess at the right compression and Chroma subsampling settings based on my visual evaluation of the complexity and type of image. But, I don't trust to judgement and experience, I look at the compress and saved image to verify that no damage occurred. In my case, I can see damage, I would say about 2% of the time, so I alter the settings until it goes away. As the JPEG FAQ says, destruction is worst when resaving with slightly different parameters at the higher quality values, counterintuitively. P.S. Thanks for your comments in the PaintShopPro thread. Mine about DCNR? If yes, you're welcome. As to the JPEG FAQ, can't speak to that. I understand it conceptually but not at all in a way I can use the knowledge in a practical example. -- HP, aka Jerry |
#32
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What program is best at JPEG compression?
In article , HEMI-Powered wrote: Mike S. added these comments in the current discussion du jour ... In article , HEMI-Powered wrote: Until I started reading posts in this thread, I was unaware that there are ANY programs that can alter a JPEG without having to recompress the entire image. I can see your point about a localized change like the small parts of an image that had red eye removed, but I would think that you are right that any change that affects literally every pixel in the image, which would happen in your example of changing colors, would require a complete recompress. Well, they _claim_ that they do so, but I have not been obsessive enough to try to verify it. Conceptually, though, I don't understand how Huffman encoding would even allow you to change _any_ pixel values in a bitmap and not have it require changing the rest of the compressed data. That's what I always thought, until I read about these magic programs in this thread. I'm no expert and not interested in trying to verify the veracity of the claims because my work isn't such that would be helped. But, in keeping with my general philosophy that learning is a life-long endeavor, if somebody has invented a better mouse trap, I'm interested enough to at least listem. JPEG Wizard's claims for lossless processing are quite clear. Photoline 32 suffers from poor translation from German, both on their web site and the help files. A strict reading would suggest that only crop and rotate functions are lossless, which is not a unique achievement. But they talk about changed and unchanged "JPEG data" which probably means something more exact in the original German. |
#33
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What program is best at JPEG compression?
Mike S. added these comments in the current discussion du jour
.... That's what I always thought, until I read about these magic programs in this thread. I'm no expert and not interested in trying to verify the veracity of the claims because my work isn't such that would be helped. But, in keeping with my general philosophy that learning is a life-long endeavor, if somebody has invented a better mouse trap, I'm interested enough to at least listem. JPEG Wizard's claims for lossless processing are quite clear. Photoline 32 suffers from poor translation from German, both on their web site and the help files. A strict reading would suggest that only crop and rotate functions are lossless, which is not a unique achievement. But they talk about changed and unchanged "JPEG data" which probably means something more exact in the original German. Mike, sorry to still be dense, but is the rotate general or in 90 deg increments? The latter is easily done, I'm no mathemetician but I can't imagine moving all those pixels/bytes around an arbitrary number of degrees without destroying the compression scheme that must get load in along with EXIF and the actual image. I can visualize crop being lossless, however, IF it runs along 8x8 and/or 16x16 pixel boundaries that are the foundation of JPEG's compression algorithm. Again, I'm neither a mathemetician or a JPEG guru so I could be entirely all wet here. Again, guys, this has been an interesting thread to kinda just look in on. The entire notion of a lossy compression scheme like JPEG and the math background I do have from engineering school 40 years ago tells me that to take all the compressed gobbledegook that's in the file, uncompress it to even to a rotate or crop, then save some of it back without messing up even one other pixel seems like magic and a dream come true. Thanks for the background. -- HP, aka Jerry |
#34
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What program is best at JPEG compression?
Fed-Up-With-Corel added these comments in the current discussion
du jour ... AFAIK only on selective compression areas, or limited area processing such as red-eye removal. Then again, it really isn't an editor, per se; more of an image manipulator and processor. I'd imagine if you were to make any global change, such as color balance adjustment, that would require reprocessing in order to save the modified image. Correct. If you do a global change then yes, the whole image would have to be ran through the JPEG routine again. The upside is that when using "Save" (not "Save-As") the same compression level that was used on the original will still be applied to the result without you having to guess or do a thing. Isn't using Save vs. Save As inherently dangerous? If anything at all goes bump in the night during the (re)Save, your original is lost forever. I would imagine that it would be a damn good idea to copy your file(s) to a temp folder just in case. Often I only need to use the clone-tool to remove a small fence-line or power-wire. Or its "Repairing Brush" (same as a healing-brush) to remove a few harsh lines in a face. Maybe get rid of that erroneous spot in the sky or defect in a flower petal, or add a small bit of text for documentation. Why recompress the whole image for that? PhotoLine 32's authors found a way around the image degradation caused by re-saves of JPG data. There are times that, as meticulous as I am to always work off of copies of the original, that on rare occasions when in a hurry I realize that I accidentally saved my edited and downsized work over the original. That's the danger I was talking about, but instead of inadvertantly overwriting the old file, you'd be doing it intentionally. Seems naive on my part, maybe, but that seems like an invitation for a visit from Murphy. After that wave of fear and anguish washes over me then I remember, "Oh, I'm using PL32. No harm done." I just undo all my edits and save the original again. Hit redo a few times to get back to where I was (or use the Undo-List for all this if there are many edits), and save my edited image under a different name or folder as I originally intended. Not a thing harmed to the original. Just as if it came right from the camera. You can't do that with any other advanced image editor on the planet. In my normal processing, before I'm finished with a picture, I will do a Save, not Save As, periodically and especially before I do something really drastic in case the Undo function fails or, in PSP 9's case, something higher up in the History Pallette fails and all is lost. But, if I'm about to do some serious experimentation to go in a couple of directions to see what works best on a complicated edit, I'll do a Save As to a different file name for safety. If you're a PSP user, you'll understand why my real standard "save" function is the JPEG Optimizer because it gives me not only easy access to Chroma subsampling, but a real- time finished file size in full bytes, not KB, which I find indespensible in judging how much to compress a given image, based on long past experience. Please realize that I'm hardly refuting anything you or anyone is saying, I'm just asking questions and commenting on what I've personally seen and done. All this stuff that has been transpiring in this thread is fascinating to me, even if I never acquire any of the software. -- HP, aka Jerry |
#35
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What program is best at JPEG compression?
On Jul 24, 5:48 pm, "HEMI-Powered" wrote:
.... All good apps can do lossless rotation, in 90 degree increments. If Irfanview can do an arbitrary rotation losslessly, I'm not aware of it, Bill. ... Irfanview only offers the following losslessly: Flip horizontally or vertically. Rotate 90, 180, or 270 degrees. It works as you expect. Alan |
#36
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What program is best at JPEG compression?
In rec.photo.digital HEMI-Powered wrote:
All good apps can do lossless rotation, in 90 degree increments. If Irfanview can do an arbitrary rotation losslessly, I'm not aware of it, Bill. Which did you mean? Yes, Irfanview does 90/180/270 degrees, or vertical/horizontal flip. Just like PSP, apparently. (I have PSP 9 but don't use it much.) 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. |
#37
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What program is best at JPEG compression?
Alan Meyer added these comments in the current discussion du
jour ... On Jul 24, 5:48 pm, "HEMI-Powered" wrote: ... All good apps can do lossless rotation, in 90 degree increments. If Irfanview can do an arbitrary rotation losslessly, I'm not aware of it, Bill. ... Irfanview only offers the following losslessly: Flip horizontally or vertically. Rotate 90, 180, or 270 degrees. It works as you expect. That's what I thought, Alan. Most/all "good" graphis programs work that way because, if I have my limited JPEG technical spec knowledge right, a rotation like you describe can be done by setting a switch in the file to tell whatever is trying to open/view it to do the flip, mirror, or 90 deg rotates. -- HP, aka Jerry |
#38
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What program is best at JPEG compression?
Bill Tuthill added these comments in the current discussion du
jour ... In rec.photo.digital HEMI-Powered wrote: All good apps can do lossless rotation, in 90 degree increments. If Irfanview can do an arbitrary rotation losslessly, I'm not aware of it, Bill. Which did you mean? Yes, Irfanview does 90/180/270 degrees, or vertical/horizontal flip. Just like PSP, apparently. (I have PSP 9 but don't use it much.) Interesting, I have Irfanview but have never installed it! 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. As I said earlier, I don't use the lossless rotate of PSP 9 so I don't know if it does or doesn't clip pixels but your logic strongly suggests that any real implementation of the JPEG standard would probably suffer from that. In my hobby of car pictures, if I can, I include about 20-25% space all the way around the car so I can crop for best composition in PSP 9. Of course, it helps a whole lot to do the basic compose at the time I shoot the pictures grin but I'm generally so pressed for time that I try to take advantage of either 4 mega pixels (usually) or 8 MP having more than enough pixels so that I can do a major crop and still not drop below the larges size I generally save to, 1600 x 1200. So, all that is to say that if PSP 9 were clipping edge pixels at all, I'd likely not notice it. BTW, you've said 8x8 a couple of times. Excuse my ignorance again, but I thought that the JPEG spec allowed both 8x8 and 16x16 blocks to be considered when deciding which pixels to throw away. Or, am I mixing this up with something else? If I am right, I have no idea if an image could have both block sizes in the same file or not. As I said, my math knowledge is what I needed to learn in engineering school a long time ago, so I just fly by the seat of my pants on all these quality issues and judge by eye. Naturally, I DO zoom in and out and such and I DO look for obvious problems like aliasing, and I DO look for JPEG artifacts after I save but before I blow the in-memory bitmap away. -- HP, aka Jerry |
#39
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What program is best at JPEG compression?
James Silverton wrote:
Matt wrote on Tue, 24 Jul 2007 14:46:19 GMT: MI David J Taylor wrote: ?? imbsysop wrote: ?? [] I've always thought jpeg and its compression algorithm ?? were subject to ?? a general standard and not to any program makers' fantasy ?? ..???? ?? ?? There is a standard, but with a large number of different ?? choices. For example, you can change the colour ?? resolution relative to the luminance resolution. How ?? different programmers interpret "95% quality" is up to ?? them, so it's entirely possible that different programs ?? will better suit different images. It is an interesting question as to which is the best general method since *most* people won't want to use more than one technique. It does beg the question of what is wanted. Is the "best" method that which produces the smallest result or some sort of compromise among size, resolution and color resolution etc.? Also a good point - what comprises the "best" compression is entirely subjective. Only way to really answer the question is for a person to try the options for him/herself, and decide what works best for him/her. |
#40
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What program is best at JPEG compression?
In article , HEMI-Powered wrote: Mike S. added these comments in the current discussion du jour ... That's what I always thought, until I read about these magic programs in this thread. I'm no expert and not interested in trying to verify the veracity of the claims because my work isn't such that would be helped. But, in keeping with my general philosophy that learning is a life-long endeavor, if somebody has invented a better mouse trap, I'm interested enough to at least listem. JPEG Wizard's claims for lossless processing are quite clear. Photoline 32 suffers from poor translation from German, both on their web site and the help files. A strict reading would suggest that only crop and rotate functions are lossless, which is not a unique achievement. But they talk about changed and unchanged "JPEG data" which probably means something more exact in the original German. Mike, sorry to still be dense, but is the rotate general or in 90 deg increments? It's in 90 degree increments as you would suspect. |
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