If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#21
|
|||
|
|||
Compression in JPEG files in digital cameras
David J Taylor added these comments in the current discussion du
jour ... What I have found in practice is that using the maximum resolution with the "normal" quality setting can beat the lower resolution with the "fine" quality setting. Of course, this is highly camera dependant, and you should test for yourself. My theory behind this is that running at the maximum resolution, you are more limited by the MTF of the lens and other components, so there is relatively less high-frequency component in the image, and that the JPEG algorithm does not need to work so hard to compress the data, and can therefore provide a higher quality image. So my recommendation to the OP is to stick with maximum resolution (3000 x 2250), and to make a series of test photos at the different quality (JPEG compression) levels, and see where you want to draw the line between file size and image quality. Include both sharp edges and subtly coloured (or even varying grey) areas in your test image. I have found that the "normal" quality setting is satisfactory on the Nikon cameras I have owned - your camera and image quality requirements may differ. We've talked about this before, and agreed to disagree. The think that I DO agree - strongly - with you about is to test, test, and test some more. It is ultimately the opinion of the OP what constitutes "quality" or "defects", we're all here to help, hopefully clarify, but also hopefully not confuse him. For the records, again I do not dispute you, I find it best on my Rebel XT to shoot at 4 rather than 8 MP because it is too much bother to take the pains to resample down to my usual 1400 x 1050 final size. Doing it in one fell swoop is almost guaranteed to introduce aliasing because few resampling algorithms can take out so much data without messing up parts of the very fine detail. In my world of car pictures, where I see it is in slightly off- horizontal chrome moldings on the side of the car, grille, or windshield. We each do what we fine works best for us, yes? Nikon do seem to have the many parameters you can adjust in the JPEG algorithm very well chosen. I was pretty surprised that my Rebel XT can't save to TIFF but only mildly miffed that it didn't have a 3rd, higher-compression- thus-lower-quality image. I did my usualy testing the first day at 2, 4, and 8 MP and both JPEG settings, made an initial eval, then went and shot some real cars at each, came home and looked at them. I will say this about more MP: I like to include absolutely as much AROUND my cars as I can fit within the confines of the space I have, preferring to do my final crop for best composition in the "digital darkroom" whilst also allowing enough to crop correctly after doing something like perspective correction. So, Since I finish at about 1.5 MP but shoot at 4, I'm more than OK. And, if I ever decide I'd like to re-edit to, say 3 MP, I can also do that. Now, if an occasion arises where I do not have enough telephoto, I will go up to 8 to get an effective increase in "focal length" by simply cropping out my smallist image from the BIG one. -- HP, aka Jerry |
#22
|
|||
|
|||
Compression in JPEG files in digital cameras
Don Stauffer in Minnesota added these comments in the current
discussion du jour ... This is a complicated question, and not suited to quick answers- I'd get a decent book on digital photography. Actually, the Dummies Guide series has a reasonable book on the subject. For this OP, it may be quite simple. It's fine if the OP wants to buy a book, probably a real good idea to learn the gentle art of digital photography. However, few books can adequately illustrate the effects of excessive compression, and a half-hour shooting a few dozen test shots around the house and yard can be very instructive to a new user. After all, it is THEIR definition of "good" and "bad" that matters, not all of us would-be "experts." Briefly, there are two different ways of reducing the size of the file (memory size) of an image. One method is to "downsample", or average pixels to create a new array of numbers with fewer pixels. All the pixels in the image chip are used, but the downsampling or averaging math reduces the "resolution" or sharpness of the image. Data compression schemes such as JPEG do not downsample in the same way. Depending on the subject a jpeg will retain all or most of the resolution. However, subtleties of color disappear, gradients of color or brightness get flattened, and little regions of the wrong color begin cropping up. Jpeg is a lossy compression scheme, meaning this loss of image quality cannot be reversed after the image file is compressed. There ARE other compression schemes that ARE reversible. With the cheapness of very large memory cards these days, and also large memory banks for computers, there is little reason to downsample in the camera, or to use excessive values of compression (many cameras allow you to select how much compression to use). The most common advice these days is to shoot full resolution (the 3000 x 2250 mentioned), and select the least amount of jpeg compression. This is frequently called picture quality, as in super high quality, high quality, medium, or some such combination of words. -- HP, aka Jerry |
#23
|
|||
|
|||
Compression in JPEG files in digital cameras
HEMI-Powered wrote:
[] For the records, again I do not dispute you, I find it best on my Rebel XT to shoot at 4 rather than 8 MP because it is too much bother to take the pains to resample down to my usual 1400 x 1050 final size. Doing it in one fell swoop is almost guaranteed to introduce aliasing because few resampling algorithms can take out so much data without messing up parts of the very fine detail. In my world of car pictures, where I see it is in slightly off- horizontal chrome moldings on the side of the car, grille, or windshield. We each do what we fine works best for us, yes? [] I was pretty surprised that my Rebel XT can't save to TIFF but only mildly miffed that it didn't have a 3rd, higher-compression- thus-lower-quality image. I did my usualy testing the first day at 2, 4, and 8 MP and both JPEG settings, made an initial eval, then went and shot some real cars at each, came home and looked at them. Jerry, TIFF doesn't really help if it's only 8-bit depth - as the best quality JPEG has so little loss. RAW would be the next step up in saved image quality, but it has the overhead of requiring more processing which I think both you and I try and minimise. Have you ever gone back and revisited the resolution and quality settings? This is something I keep meaning to do as I gain experience, but somehow I never get round to it! I wonder if we would make the same choices a second time, particularly on JPEG quality setting? Yes, we agree to disagree on shooting - I go for highest resolution with "normal" JPEG quality. I leave any resampling up to the display software - indeed I wrote my own simple slide-show program so that I had control over the display process. http://www.david-taylor.myby.co.uk/s...html#SlideShow What works best for you, is best for you, and I respect that. Cheers, David |
#24
|
|||
|
|||
Compression in JPEG files in digital cameras
HEMI-Powered wrote:
added these comments in the current discussion du jour ... I need some help in explaining the JPEG compression feature in digital cameras. My camera (which likely is similar to most others) has the feature to compress the photo JPEG files in the storage card. It also has the choice to have different pixel sizes (example: 3000x2250, 2000x1500, 1024x768, etc). What is the difference of the above two features? If you store a 3000x2250 pixel data in compressed mode, does it loose its quality? Can it be re-instated to full uncompressed size without loosing photo quality?. When I compressed the data, it will fit more pictures in a single storage card. But, is it the same if I choose 2000x1500 pixel and no compression instead? Thanks for info. Resolution is measured by horizontal and vertical pixels for an image, the area of which constitutes mega pixels. JPEG compression is how much or little the uncompressed data is made smaller. Since JPEG is a so-called "lossy" format, it literally throws away pixels in order to drastically shrink the file size. The idea of the algorithm is to choose pixels to disgard that have a mathmatical probability of not being noticed by the human eye. However, when compression begins to get even moderately high, defects begin to appear, commonly called "JPEG artifacts", artifact meaning "what is left behind". This can easily be seen by blobs, streaks, blurry areas, minor destruction of fine detail, and sometimes posterization. "Better" digital cameras will give you choices as to how much to compress for a given mega pixel image. Lots of words used but "basic", "normal", and "fine" are common. I don't think any cameras tell you the actually number they use nor the Chroma subsampling they use, but under most circumstances, one can quickly show themselves that "basic" is pretty awful, "normal" MAY produce artifacts 5, 10, 15% of the time, and "fine" rarely does. However, many - not all - of the less expensive P & S cameras only give you marketing BS like "good", "better" and "best", but what they're really doing is maintaining the same JPEG compression but upping the MP. The reason that so many lower cost but high MP cameras do that is that they also want to advertise how many pictures you can fit on even a small memory card. I'm not sure about the rest of your question to exampand more on my answer. Some cameras allow TIFF, which is lossless, and even better cameras - certainly DSLRs - can also save in RAW. Without starting another religious war, if you can get by with JPEG and it fulfills what you want and need the camera to do for you, you'll be just fine. It is universally readable, lots of free or almost free editing apps as wells as commercial apps, and you can save money on memory if that is a consideration. But, since I know of NO camera buyer who isn't interested in the best possible quality, I would look for cameras that offer a choice of compression so that you can run some tests for yourself and make up your own mind. I vote for maximum resolution, minimal compression, and buy more, or larger, cards. With 2GB SD cards selling for about $20 (US), these days, the question seems moot. |
#25
|
|||
|
|||
Compression in JPEG files in digital cameras
HEMI-Powered wrote:
David J Taylor added these comments in the current discussion du jour ... What I have found in practice is that using the maximum resolution with the "normal" quality setting can beat the lower resolution with the "fine" quality setting. Of course, this is highly camera dependant, and you should test for yourself. My theory behind this is that running at the maximum resolution, you are more limited by the MTF of the lens and other components, so there is relatively less high-frequency component in the image, and that the JPEG algorithm does not need to work so hard to compress the data, and can therefore provide a higher quality image. So my recommendation to the OP is to stick with maximum resolution (3000 x 2250), and to make a series of test photos at the different quality (JPEG compression) levels, and see where you want to draw the line between file size and image quality. Include both sharp edges and subtly coloured (or even varying grey) areas in your test image. I have found that the "normal" quality setting is satisfactory on the Nikon cameras I have owned - your camera and image quality requirements may differ. We've talked about this before, and agreed to disagree. The think that I DO agree - strongly - with you about is to test, test, and test some more. It is ultimately the opinion of the OP what constitutes "quality" or "defects", we're all here to help, hopefully clarify, but also hopefully not confuse him. For the records, again I do not dispute you, I find it best on my Rebel XT to shoot at 4 rather than 8 MP because it is too much bother to take the pains to resample down to my usual 1400 x 1050 final size. Doing it in one fell swoop is almost guaranteed to introduce aliasing because few resampling algorithms can take out so much data without messing up parts of the very fine detail. In my world of car pictures, where I see it is in slightly off- horizontal chrome moldings on the side of the car, grille, or windshield. We each do what we fine works best for us, yes? Nikon do seem to have the many parameters you can adjust in the JPEG algorithm very well chosen. I was pretty surprised that my Rebel XT can't save to TIFF but only mildly miffed that it didn't have a 3rd, higher-compression- thus-lower-quality image. I did my usualy testing the first day at 2, 4, and 8 MP and both JPEG settings, made an initial eval, then went and shot some real cars at each, came home and looked at them. I will say this about more MP: I like to include absolutely as much AROUND my cars as I can fit within the confines of the space I have, preferring to do my final crop for best composition in the "digital darkroom" whilst also allowing enough to crop correctly after doing something like perspective correction. So, Since I finish at about 1.5 MP but shoot at 4, I'm more than OK. And, if I ever decide I'd like to re-edit to, say 3 MP, I can also do that. Now, if an occasion arises where I do not have enough telephoto, I will go up to 8 to get an effective increase in "focal length" by simply cropping out my smallist image from the BIG one. Why does a person buy a DSLR, and then shoot at a resolution barely better than the early digital cameras produced? If you want only 1.5mp, why spend money on a DSLR? Even a $99 P&S camera will give better images than you get that way. I can only conclude that for your needs, small size is more important than image quality. I can only assume that you only capture images for web use. |
#26
|
|||
|
|||
Compression in JPEG files in digital cameras
David J Taylor added these comments in the current discussion du
jour ... I was pretty surprised that my Rebel XT can't save to TIFF but only mildly miffed that it didn't have a 3rd, higher-compression- thus-lower-quality image. I did my usualy testing the first day at 2, 4, and 8 MP and both JPEG settings, made an initial eval, then went and shot some real cars at each, came home and looked at them. Jerry, TIFF doesn't really help if it's only 8-bit depth - as the best quality JPEG has so little loss. RAW would be the next step up in saved image quality, but it has the overhead of requiring more processing which I think both you and I try and minimise. Both ordinary JPEG and TIFF are both 8-bit. I only mentioned TIFF, either the uncompressed kind or LZW, as an alternative to the OP or any lurkers who want a simpler lossless file system than RAW, Have you ever gone back and revisited the resolution and quality settings? This is something I keep meaning to do as I gain experience, but somehow I never get round to it! I wonder if we would make the same choices a second time, particularly on JPEG quality setting? Yes, David, as recently as this spring as I was getting ready for the summer car show season. It isn't that I dispute you at all, you're much more skilled and knowledgeable than me, it is that MY experience shows that the amount of work necessary to get an 8 MP image down to my 1.5 MP finished size without introducing aliasing and other undesirable non-compression artifacts just isn't worth my time and effort. I never revisited the lower quality, i.e., higher compression, option on my Rebel because I could easily see JPEG compression artifacts at a large enough percentage that I didn't want to risk blowing otherwise good pictures. As you and others have so correctly pointed out, memory is so cheap, that it really doesn't matter if the image is 500KB or one meg. Yes, we agree to disagree on shooting - I go for highest resolution with "normal" JPEG quality. I leave any resampling up to the display software - indeed I wrote my own simple slide-show program so that I had control over the display process. http://www.david-taylor.myby.co.uk/s...ging.html#Slid eShow What works best for you, is best for you, and I respect that. Thanks for the link, David. And, I respect YOUR preferences. People in this NG, like most Usenet NGs, get along a whole lot better if they respect each other's rights and freedoms to do things in alternate ways, and I think you and I have previously agreed that there NEVER is one or even two "right" ways to do anything. And, as you so eloquently say, "what works best for you, is best for you", where "you" means anyone anywhere anytime doing anything. Have a great day! -- HP, aka Jerry |
#27
|
|||
|
|||
Compression in JPEG files in digital cameras
Ron Hunter added these comments in the current discussion du
jour ... Why does a person buy a DSLR, and then shoot at a resolution barely better than the early digital cameras produced? If you want only 1.5mp, why spend money on a DSLR? Even a $99 P&S camera will give better images than you get that way. I can only conclude that for your needs, small size is more important than image quality. I can only assume that you only capture images for web use. There are many reasons why a DSLR is preferable besides just the mega pixels it can produce. And, I've stated enough times why I prefer 4 to 8 generally, so I shan't repeat myself here. Suffice to say that there are times I go to 8 and as I just replied to David Taylor, I DO perform controlled tests on a number of key set-up parameters to determine what seems to work best for the particular photographic situations I find myself in as well as my current level of skill in PSP 9. David said it best: what works best for you, is best for you. As to the conclusions you reached, be wary of jumping to incorrect conclusions based on no facts and only unfounded assumptions. If you don't know me or the reasons I do what I do, as evidenced by periodic posts I make on the subject of mega pixels, then you might leap to a wrong view of my intelligence either when purchasing a camera or using it. I have found in life that it usually is not wise to take extreme views and verbally spank others who happen not to agree with me. -- HP, aka Jerry |
#28
|
|||
|
|||
Compression in JPEG files in digital cameras
HEMI-Powered wrote:
Both ordinary JPEG and TIFF are both 8-bit. I only mentioned TIFF, either the uncompressed kind or LZW, as an alternative to the OP or any lurkers who want a simpler lossless file system than RAW, TIFF is not fixed to a given bit depth. I often create 16-bit TIFF images. The compression type is not limitted in TIFF either. Photoshop will create 16-bit images and use no compression, LZW compression or ZIP compression. TIFF can be used with ANY compression algorithm if it is built that way ... there are just no clients that support it. Also, keep in mind that DNG, adobe's digital negative, a RAW format, also is based on the TIFF format. -- Thomas T. Veldhouse We have more to fear from the bungling of the incompetent than from the machinations of the wicked. |
#29
|
|||
|
|||
Compression in JPEG files in digital cameras
Thomas T. Veldhouse added these comments in the current
discussion du jour ... Both ordinary JPEG and TIFF are both 8-bit. I only mentioned TIFF, either the uncompressed kind or LZW, as an alternative to the OP or any lurkers who want a simpler lossless file system than RAW, TIFF is not fixed to a given bit depth. I often create 16-bit TIFF images. The compression type is not limitted in TIFF either. Photoshop will create 16-bit images and use no compression, LZW compression or ZIP compression. TIFF can be used with ANY compression algorithm if it is built that way ... there are just no clients that support it. Also, keep in mind that DNG, adobe's digital negative, a RAW format, also is based on the TIFF format. OK, but again, Thomas, I interpreted the OP as being a fairly new digital owner and thus a novice on file types, so I just mentioned TIFF as an alternative if their camera supports it. TIFF is universally recognized, although news readers cannot decode it in line, and about its only drawback other than large size is that if you want to save EXIF, you cannot use LZW compression, or at least AFAIK. I don't want to start yet another religious war about bit-length. It seems to me, though, that 16-bit color - no matter where it comes from or in what format(s) it is saved to - is a subject for VERY advanced people who have software that can correctly manipulated it. And, the person behind the camera and behind the keyboard also has to be quite a bit more knowledgeable to gain any real advantage over 8-bit. But, I have a question for you Thomas: everytime 16-bit color comes up, part of the raging debate is that most/all cameras and apps, including PS CS2, really only have 11 or 12 bits of real information, the others being basically just noise that is ignorned by the software. Has that improved in ANY format, whether it be JPEG, TIFF, or RAW? i.e., is something closer to 16-bit or true 16-bit now available for them with deep pockets? If so, could you just give me 25 words or less as a heads-up on today's status so I can go looking? Yes, I know Google is my best friend, but on things like this, it is like the old saying "I don't even know enough to ask an intelligent question", and it goes to the extreme frustration I have had for well over a year trying to find a RAW for Dummies kind of book that isn't keyed to PS CS2 or Elements that will at least get me started up the learning curve. In any event, I find these threads fascinating but always feel bad for the poor OP who has some simple or easy question like he does the size of the image or compression cause image problems? I kinda doubt that level of knowledge is ready for all of the sophisticated answers the more experienced folks have been bantering about. Yes, /I/ learn something, but a rank novice just gets totally snowed under and may feel so intimidated as to not even come back for a 2nd round of questions. -- HP, aka Jerry |
#30
|
|||
|
|||
Compression in JPEG files in digital cameras
HEMI-Powered wrote:
[] Both ordinary JPEG and TIFF are both 8-bit. I only mentioned TIFF, either the uncompressed kind or LZW, as an alternative to the OP or any lurkers who want a simpler lossless file system than RAW, OK, I appreciate that. Have you ever gone back and revisited the resolution and quality settings? This is something I keep meaning to do as I gain experience, but somehow I never get round to it! I wonder if we would make the same choices a second time, particularly on JPEG quality setting? Yes, David, as recently as this spring as I was getting ready for the summer car show season. It isn't that I dispute you at all, you're much more skilled and knowledgeable than me, it is that MY experience shows that the amount of work necessary to get an 8 MP image down to my 1.5 MP finished size without introducing aliasing and other undesirable non-compression artifacts just isn't worth my time and effort. I never revisited the lower quality, i.e., higher compression, option on my Rebel because I could easily see JPEG compression artifacts at a large enough percentage that I didn't want to risk blowing otherwise good pictures. As you and others have so correctly pointed out, memory is so cheap, that it really doesn't matter if the image is 500KB or one meg. Yes, I would expect that when using less than the native resolution of the camera, the images will be slightly sharper (meaning that there are fewer pixels covering a black-white transition), and therefore more likely to show JPEG artefacts at a particular compression (quality) level. So when using lower resolution, stick with the highest JPEG quality. Makes sense to me, anyhow! Cheers, David |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
What program is best at JPEG compression? | [email protected] | Digital Photography | 84 | August 7th 07 10:20 AM |
Controlling compression with (Nikon) digital cameras. | [email protected] | Advanced Photography | 4 | January 1st 05 04:11 AM |
Controlling compression with (Nikon) digital cameras. | [email protected] | Digital Photography | 4 | January 1st 05 04:11 AM |
best compression for saving photos in jpeg? | Brian | Digital Photography | 14 | December 24th 04 01:59 PM |
JPEG compression | James Ramaley | Digital Photography | 14 | October 26th 04 01:41 AM |