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02/01/2010 04:01:23 PM · #1 |
Question for those that understand file sizes.
The 7d is an 18mp camera. I'm not always going to want to shoot at 18mp for something that doesn't need the quality. So, I'm just wondering which jpg setting is best.
There are two Large settings and two Medium settings. Am I better to use the lower Larege setting or the higher Medium setting when wanting to save smaller files.
Thanks in advance. |
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02/01/2010 04:11:53 PM · #2 |
I just use MRAW when I wanna kick it down a bit, that drops it to about 10mpx
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02/01/2010 04:15:11 PM · #3 |
That's a tricky question without a straightforward answer.
The size (large vs medium) setting controls the resolution (dimensions) of the output image (5184x3456 on large, 3456x2304 on medium). That's straightforward and quantitative.
The quality (fine vs normal) will control the JPEG compression amount. This is where things get qualitative - maybe you can you tell the difference in fine/normal JPEG compression, maybe you can't. It affects the details in each individual image differently.
It's also basically impossible to guess to the resultant JPEG file size (talking in megabytes now, not dimension or resolution) of the output images, because that too depends on the details therein, the compression (fine/normal), and the in-camera processing (color/contrast/sharpening/etc).
Some people believe that the Medium resolution setting retains plenty of detail because the large size relies on bayer interpolation, so it's not really full detail at that size. It's just marketing.
Basically your only option is to take a few shots at both settings, compare them at 100% on a monitor and in print at various sizes, and decide what you're willing to sacrifice for smaller file sizes.
Personally I've decided that I'm happy with the detail retained in large/fine JPEGs in the 3-5MB range, while some people insist on retaining original RAW files in the 10-20MB range. It's a personal preference.
Message edited by author 2010-02-01 16:18:53. |
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02/01/2010 04:21:30 PM · #4 |
That's really a tough question, because the potential problems are entirely different. Using the large image size setting you have an 18Mpx image, but you risk JPEG artifacts due to the higher compression when you use the lower quality setting. With the Medium (but higher quality) setting, you have an 8 Mpx image, but less risk of JPEG artifacts.
Which is better depends on both what is more important to you and your end use and also on how severe the compression artifacts are at the lower quality setting. I suspect that they are only very moderate, and that you might prefer the larger file with higher compression. I'm afraid you'll really have to test in order to know for certain.
Take photos at lowest ISO of a very complex scene, one with lots of very fine detail. Do this at both settings. Examine the larger, lower-=quality image for sign of JPEG artifacts. Compare with the smaller image. Evaluate how much detail you lose in going to the smaller image. Will the smaller image suffice for your end use?
I suspect that the file size of the 8 Mpx image will be smaller, no matter how far you crank up the compression on the larger image. |
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02/01/2010 04:35:13 PM · #5 |
File sizes from the manual state:
Large = 6.6mb or 3.3mb
Medium = 3.5mb or 1.8 mb
So, the smaller Large file actually has a smaller file size than the Medium file.
Does that make a difference?
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02/01/2010 09:40:14 PM · #6 |
Those numbers are estimates and/or averages only - the JPEG file size will be different for each photo. It probably varies quite widely. Take a picture of an out of focus, white wall, and then one of a high-contrast, sharp scene with tons of detail. While compression is a very complex subject, humans can easily grasp the concept that there is a lot of information in a highly detailed photo, and a very little information in a pure white photo. The latter will result in a smaller file because compression techniques generally work by reducing redundant information.
The reason Canon must make an estimated guess of image size (megabytes) in the manual is because the consumer wants to know how many images will fit on, for instance, a 2GB card, and they don't want to hear - well it depends on many things. They want to hear "310 images at Large/Fine."
Your best option is still to take sample pictures at different settings, examine them in detail for yourself, and decide what are the best settings for you. =)
Message edited by author 2010-02-01 21:41:05. |
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