TIFF vs JEPG
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From: Raphael Bustin on 20 Apr 2006 23:50 On 20 Apr 2006 18:58:44 -0700, "Noons" <wizofoz2k(a)yahoo.com.au> wrote: >Sorry, the ones from rafe were not examples: they were totally out >of context. I did not throw rocks at yours for the simple reason that >I did not see them. Or are you and rafe one and the same? If so, >I seriously advise you to stop using various aliases: one is >enough. You can't imagine that two different people, six thousand miles apart, could *independently* call you on your mis-statements and subsequent evasion? You and Don have both made outrageous claims and failed to back them up with a *single example.* Scott and I have provided, collectively, at least a half dozen. You and Don have been asked numerous times to provide examples. But all you do is dis' ours. Called on your ignorance, you whine, obfuscate, and smear. What a guy. rafe b www.terrapinphoto.com
From: Bruce on 21 Apr 2006 09:09 Don, Deny your aggressiveness all you want. Here you are accusing me of not having read the thread, which is an unfounded insult. Don wrote: > On Wed, 19 Apr 2006 12:01:13 -0400, Bruce <XXbg2gX(a)XvirginiaX.Xedu> > wrote: > >> Yes, everyone agrees that with high compression JPG artifacts can be >> objectionable. But the point is that at low compression the quality can >> be so good that any data loss is imperceptible even after zooming in. > > That was never the subject, Bruce. It's an unrelated tangent. Please > read the messages. Here is a statement about tiff vs jepg (which is the subject line of the thread): > If you blow up the images to the point where you can see >>individual pixels, you will see that some of the pixels are >>different in the two images. But even then, unless you know >>in advance, you won't be able to tell which was the original, And here is a direct quote from you attacking it: > That's just patently false! > > At 100% magnification (i.e. 1:1) even a JPG image at lowest > compression (i.e. highest quality) stands out like a sore thumb when > compared to the original. Numerous people have posted examples to show that this is not necessarily the case for high quality jepgs. Your response has been to question the "veracity" of their examples. Well my own experience is that you are wrong. If you are interested is "truth" and "facts" post examples to educate us and show us conditions where a single high quality jepg compression does cause visible image degradation. My understanding is that the jepg standard uses several separate compression schemes most of which are disabled at the higher quality settings, but each software package implements the details differently, hence the need for actual testing.
From: Raphael Bustin on 21 Apr 2006 09:24 On Fri, 21 Apr 2006 08:11:06 -0500, Alex <Alex(a)Alex> wrote: >If I may digress for a moment: how did you make this scan (what scanner [looks >like a KM Scan Elite] and what photographic material were used)? Did you edit >the scans in any way? >It looks extremely noise-free, whereas all my scans suffer from heavy 'color >noise'. I use the KM Scan Elite 5400 old model, and color negatives only of >different brands. The problem isn't with your scanner. Color negatives will always show more noise than positives when scanned, because negatives have a much smaller density range and therefore need more tonal expansion (decompression.) AFAIK, most of Scott's images come from digital capture. Scott's a wizard at stitching these to form large, seamless composites. That's why his images are so clean. rafe b www.terrapinphoto.com
From: Scott W on 21 Apr 2006 10:33 Raphael Bustin wrote: > On Fri, 21 Apr 2006 08:11:06 -0500, Alex <Alex(a)Alex> wrote: > > > >If I may digress for a moment: how did you make this scan (what scanner [looks > >like a KM Scan Elite] and what photographic material were used)? Did you edit > >the scans in any way? > >It looks extremely noise-free, whereas all my scans suffer from heavy 'color > >noise'. I use the KM Scan Elite 5400 old model, and color negatives only of > >different brands. > > > The problem isn't with your scanner. > > Color negatives will always show more noise than > positives when scanned, because negatives have > a much smaller density range and therefore need > more tonal expansion (decompression.) > > AFAIK, most of Scott's images come from digital > capture. Scott's a wizard at stitching these to form > large, seamless composites. That's why his images > are so clean. > Yup, digital. I have film scans as well but they are not nearly as clean. I figured these would be good test images since they have much less noise and far more detail then any scan of 35mm film that I have ever seen. With a very clean image it will be easier to see how much is loss saving it as a jpeg. Noons would have us believe that you can't zoom in on a jpeg and see the same level of detail that you can in a tiff, clearly he totally wrong. FWIW when I scan my work flow is to scan directly into Photoshop, adjust and then save as a HQ jpeg. I did a bunch of testing and found no real advantage of saving as tiffs. When I stitch I will often stitch into a psd file, more for the layers then anything else. For my test image I stitched directly into a 16 bit / color tiff, something that I can do but rarely do. Scott
From: Don on 21 Apr 2006 14:12
On Fri, 21 Apr 2006 00:44:18 +1200, Colin D <ColinD(a)killspam.127.0.0.1> wrote: >I loaded both of Rafe's images, the tif and the jpg into Photoshop, >They are both exactly 1001 pixels square, so if scanned at 4000 ppi the >crops represent a 0.25-inch square piece of the negative or slide, and >when viewed at 100% on my monitor at 72ppi, the magnification is >4000/72, or 55x. Without getting into details, for an objective test you have to scan raw, in other words disable everything. One common trap often missed is interpolation. There are many such pitfalls which is why testing parameters are so crucial. This goes for any objective test. >Then I made a duplicate image in PS of the tif file, and saved it as a >level 12 jpg, wrote it to disk and then reloaded it into PS. > >OK. Results: at 400% on the screen, each pixel was visible, and at that >level there was no discernible difference among the three images side by >side There are many reasons why that's not a good procedure (the same goes for layers) but I won't get into any of that now. Instead of side by side, open both images independently. Next, click on the magnifier and set the checkmark "Resize windows to fit". Finally, double-click the magnifier for each to blow up to 100% and - if the images are larger than the screen - this will also automatically align and overlay them. NOTE: Photoshop (at least my version) may be cranky when lining up images using the above process. This alignment will *only* work if you haven't changed image size after you opened them! There's a workaround but the easiest thing is to just do exactly as I explained above. After that use Control/Tab to flip between the two images. If you scroll them both by the same amount (scroll, Control/Tab, scroll), they will remain aligned. Look for "lines" i.e. sudden and distinct borders between neighboring areas. That's the JPG 8x8 square. Too much magnification may be as bad as too little. I find that (for all purposes actually!) ~300 magnification seems to work the best. >Under blind test >conditions I don't think anyone could nominate which was which. As I also mentioned even if everything was done properly up to this point a lot depends on image content. If you're looking at "black cats in tunnels" or "polar bears in snow" you won't see much. But even if you're looking at an image segment where JPG artifacts are most pronounced it's still a subjective call unless you know what to look for. But to a trained eye JPG stands out like a sore thumb. >An interesting point, though. I understood that for the best jpg >results the pixel dimensions should be divisible by 8, which 1001 >certainly isn't. Since the jpg's remained at 1001 pixels, the jpg >process didn't crop the image, so maybe it ignores the extra pixel, and >just operates on the 1000 x 1000 area. > >Anybody know? That's not quite correct. JPG itself works by dividing the image into 8x8 squares and compressing them individually. That's why the border between two neighboring squares is visible. In general, the algorithm only takes into account pixels within that 8x8 square. The square next to it is "on its own" which is why there is a border. If the image is not divisible by 8 there are a number of strategies to compensate for the missing pixels but that should not affect the rest of the image. Don. |