Compression in JPEG files in digital cameras
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. |
Compression in JPEG files in digital cameras
wrote in message ups.com... 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. Don't ask much, do you? Jpg is a lossy form of saving the picture - Google on 'explanation of jpg' and it will give you the detail - as distinct from compressed per se. As you have lost picture info you cannot get it back, so there is no way to regenerate the original intact. If you want to save in a non-compressed format you need to use TIFF (OK it is slightly compressed) or better still RAW which is just the raw data off the sensor without adjustment. The differences in resolution affect file size and quality of reproduction. 3000x2250 is about 6.7Mp, 2000x1500 is 3Mp, etc. For 'normal' printing at full frame (i.e. without cropping) 3Mp will produce an acceptable colour picture at A4 or thereabouts. For most day-to-day use 5Mp is enough, 6Mp is really the limit for a compact. If you go much higher than that you start to get digital noise in saturated colours due mainly to thermal effects in the sensor. Another point that is often missed is that the lenses on many compacts - particularly at the cheaper end of the market - often do not have the resolution in themselves to match the resolution of the sensor. In a nutshell, use RAW or TIFF if your camera has it, otherwise go for the best quality that the camera can provide - memory cards are dirt cheap these days. -- Woody harrogate3 at ntlworld dot com |
Compression in JPEG files in digital cameras
wrote in message ups.com... 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. All jpegs have some compression. In simple terms, because I am, jpeg saving examines the image in 16 pixel groups and assess how much alike the colours are. Just how much the need to be is the compression factor high compression means they dont have to be as close as low compression. What it does now it save one pixel of that colour and notes where the simler pixels are then dumps them. When you reopen the image the missing pixels are replaced with copies of that saved one. Images with large expenses of simler colour like sky and sand compress down to a smaller file size at the same level of compression than a image busy in fine detail. This happens each time you save as jpeg, losing some detail each time until the image is ruined so dont keep making changes and resaving none of this Makes any difference the dimensions such as 3000 x 2000 adding the compression and smaller dimensions will make a mush smaller file. When it comes to printing the more pixels the better if you want a larger print as we use a print scaling factor referred to as ppi pixels per inch. That how many pixels we pack into a SQ inch of paper. for a print that we will inspect at upto arms length we need 200ppi. this means the finest detail in the print will be 200th of an inch. so for a 10 x 8 print we need 10 x 200 = 2000 pixels wide by 8 x 200 = 1600 pixels high. I hope that is of some help |
Compression in JPEG files in digital cameras
wrote:
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? Smaller files size/pixel size equals poorer quality.On the other hand, it means more pics on the card. With the cost of memory so low now, it isnt really much of a feature now, as there is no point in saving in smaller formats. If you store a 3000x2250 pixel data in compressed mode, does it lose its quality? Yes. Any system that saves as jpeg will be a compromise between file size and quality. Can it be re-instated to full uncompressed size without loosing photo quality?. No. 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? No. As above, if you save as a jpeg, you will lose quality. For the best quality, pics should be saved in RAW format, or any of the other proprietary no-loss formats that camera makers use. Alan. -- To reply by e-mail, change the ' + ' to 'plus'. |
Compression in JPEG files in digital cameras
On Sat, 18 Aug 2007 11:55:45 -0700, aniramca wrote:
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. It will uncompress to the full resolution - however it will not be an exact replica of the original image. JPEG is a 'lossy' compression algorithm - meaning that some detail is lost in the act of compressing the data. There are 'lossless' compression schemes as well, but the level of compression with them is generally considerably less. From a practical standpoint, you can do a lot of compression on a JPEG image before you see noticeable loss of information. Before I got a camera capable of saving RAW images, I always chose the highest resolution and the smallest amount of compressin on JPEG images - now I simply save nearly everything in RAW - even though it does take a lot of space. Memory cards are very cheap now - IMHO it is better to get some extra cards and save everything using the best method possible. I currently have 2-1gb cards and 1-2gb card for my 5mp camera - they run around $15 and $30 respectively. |
Compression in JPEG files in digital cameras
ray wrote:
On Sat, 18 Aug 2007 11:55:45 -0700, aniramca wrote: 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. It will uncompress to the full resolution - however it will not be an exact replica of the original image. JPEG is a 'lossy' compression algorithm - meaning that some detail is lost in the act of compressing the data. There are 'lossless' compression schemes as well, but the level of compression with them is generally considerably less. From a practical standpoint, you can do a lot of compression on a JPEG image before you see noticeable loss of information. Before I got a camera capable of saving RAW images, I always chose the highest resolution and the smallest amount of compressin on JPEG images - now I simply save nearly everything in RAW - even though it does take a lot of space. Memory cards are very cheap now - IMHO it is better to get some extra cards and save everything using the best method possible. I currently have 2-1gb cards and 1-2gb card for my 5mp camera - they run around $15 and $30 respectively. The resolution refers to the amount of detail captured by the sensor and saved before any compression (if any) is applied. Ultimately it will translate into how large an image you can print. Initially, large prints will lose resolution, continued enlargement will exhibit pixelation. I always shoot at maximum resolution (5mp in my case). There will be instances when lower resolutions are ultimately desired for web use or email, but this can all be done later. This has little to do with how the file is saved. Jpeg compression reduces file size from whatever lossless format the camera uses to a more manageable size. Usually, you are given a choice of 3 settings with names like fine, super fine and normal. I can't for the life of me ever see any difference between fine (the default) and super fine except a very large size difference, so I use default and if others disagree, as I'm sure they will, that's ok, but I don't want to hear about it. As mentioned elsewhere, the algorithm works by cleverly looking for adjacent pixels of close color match and combining them. As you increase the compression the quality goes down, but the appearance is quite different from low resolution. Fortunately you can easily see how this works. Save a file at least compression, then use something like Irfanview to output a series of files at decreasing quality (increasing compression). At some point you will begin to notice the deterioration. Some software will actually show you a preview of how the image will look at different degrees of compression before you save. I always save the original from the camera and avoid editing a modified jpeg a second or more time. Tiff and raw are lossless formats, but only some p&s's even offer that option, presumably since the audience for a p&s isn't likely to want to do the post processing involved, but there are exceptions. Dave Cohen |
Compression in JPEG files in digital cameras
On Sat, 18 Aug 2007 23:53:50 +0000, Dave Cohen wrote:
ray wrote: On Sat, 18 Aug 2007 11:55:45 -0700, aniramca wrote: 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. It will uncompress to the full resolution - however it will not be an exact replica of the original image. JPEG is a 'lossy' compression algorithm - meaning that some detail is lost in the act of compressing the data. There are 'lossless' compression schemes as well, but the level of compression with them is generally considerably less. From a practical standpoint, you can do a lot of compression on a JPEG image before you see noticeable loss of information. Before I got a camera capable of saving RAW images, I always chose the highest resolution and the smallest amount of compressin on JPEG images - now I simply save nearly everything in RAW - even though it does take a lot of space. Memory cards are very cheap now - IMHO it is better to get some extra cards and save everything using the best method possible. I currently have 2-1gb cards and 1-2gb card for my 5mp camera - they run around $15 and $30 respectively. The resolution refers to the amount of detail captured by the sensor and saved before any compression (if any) is applied. Ultimately it will translate into how large an image you can print. Initially, large prints will lose resolution, continued enlargement will exhibit pixelation. I always shoot at maximum resolution (5mp in my case). There will be instances when lower resolutions are ultimately desired for web use or email, but this can all be done later. This has little to do with how the file is saved. Other things being equal, a jpeg saved with more compression will show some 'blockiness' at a lower magnification than one saved with less compression i.e. higher jpeg quality. Jpeg compression reduces file size from whatever lossless format the camera uses to a more manageable size. Usually, you are given a choice of 3 settings with names like fine, super fine and normal. I can't for the life of me ever see any difference between fine (the default) and super fine except a very large size difference, so I use default and if others disagree, as I'm sure they will, that's ok, but I don't want to hear about it. As mentioned elsewhere, the algorithm works by cleverly looking for adjacent pixels of close color match and combining them. As you increase the compression the quality goes down, but the appearance is quite different from low resolution. Fortunately you can easily see how this works. Save a file at least compression, then use something like Irfanview to output a series of files at decreasing quality (increasing compression). At some point you will begin to notice the deterioration. Some software will actually show you a preview of how the image will look at different degrees of compression before you save. I always save the original from the camera and avoid editing a modified jpeg a second or more time. Tiff and raw are lossless formats, but only some p&s's even offer that option, presumably since the audience for a p&s isn't likely to want to do the post processing involved, but there are exceptions. Dave Cohen |
Compression in JPEG files in digital cameras
On Aug 18, 11:55 am, wrote:
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? Tough question. My theory is that, assuming that jpeg compression is optimized, that file size will be be the determination of image quality. So, if you are wondering which will have a better image quality: medium resolution at max quality (lowest compression) vs max resolution at med quality (med compression), I would guess that the one with a larger file size. Of course, you should also do a sanity check by viewing both files resampled to the same resolution (with antialiasing). For example, to your screen resolution (1024x768 or whatever). |
Compression in JPEG files in digital cameras
|
Compression in JPEG files in digital cameras
Bucky wrote:
On Aug 18, 11:55 am, wrote: 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? Tough question. My theory is that, assuming that jpeg compression is optimized, that file size will be be the determination of image quality. So, if you are wondering which will have a better image quality: medium resolution at max quality (lowest compression) vs max resolution at med quality (med compression), I would guess that the one with a larger file size. Of course, you should also do a sanity check by viewing both files resampled to the same resolution (with antialiasing). For example, to your screen resolution (1024x768 or whatever). 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. Nikon do seem to have the many parameters you can adjust in the JPEG algorithm very well chosen. Cheers, David |
All times are GMT +1. The time now is 03:53 AM. |
Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
PhotoBanter.com