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03-10-2013, 03:52 PM   #1
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Beginner Lightroom question

First let me say that I am quite new to most of this and I have been using the Lightroom 4 trial for a couple of weeks now. Admittedly, I have not had a chance to get a Lightroom book and truly learn how to use it properly.

Now, my question is in regards to the file size of jpegs that Lightroom exports. Let me explain what I have done to help paint the image of the question. A couple weeks ago I went out and shot a ton of photos of ducks and geese all shot in Raw (DNG) on the K-30. When I got home I loaded them up in Lightroom and sorted through the keepers. From there I played around with some of the tools in LR and cropped a good majority of the images and then exported them to jpegs. These files were usually around 1MB or slightly less. Most of the shots were with the K-30 and the DA 55-300mm lens along with a few taken with the DA 35mm f/2.4.

Now, the other day a friend was over and I decided to play around a little bit with taking some photos of her newborn baby. She wanted me to upload them so she could show her husband. No problem I thought. So, I do basically the same thing. I just wanted to do a quick conversion to jpeg so I could upload them so I loaded them up in LR and did an Auto tone on import. Then I exported them all to jpeg so I could upload them. That is when I realized that the files were all 12-15MB which is quite large. I also played a little with a shot of a squirrel I took this morning and it exported at around 6MB but it was cropped quite a bit so I would expect that. All of the baby photos were shot with the DA 35mm f/2.4 while the squirrel was shot with the DA 55-300mm.

So, now to the basic question, why are the file sizes so dramatically different? I don't think I changed any export settings but it is possible. I see in the export popup that I can limit the file size but I don't really want to do that unless I have to. Mostly I just want to understand why this occurred so I can learn from it and expect it moving forward. Is it just some simple thing I am overlooking?

Thanks for any input.

03-10-2013, 04:09 PM   #2
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There is also a quality slider and you can reduce the amount of pixels.

If really no settings were changed then it might be the photos themselves, a photo with little details are smaller.
03-10-2013, 04:43 PM   #3
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Several things affect the final physical size of the jpeg file:
  1. The quality export setting, the higher the quality the bigger the file
  2. Any cropping that was done. This can be dramatic in reducing the file size if lots of it is cropped away
  3. The export settings themselves. It is possible to export just about any image size you want or to limit the file size if you want to do that
  4. The image itself. A jpeg of a green wall will be very tiny. A jpeg of a complex scene with lots of varied colors and details will be much bigger even if the image is the same dimensions as the green wall image.

Keep in mind that there is only a passing relationship between file size and image size. The jpeg compression is affected by the above items and thus determines the file size (megabytes). The image size (megapixels) is affected only by the size of the image from the camera and any cropping that is done to it.

It is rather easy to get a 16 megapixel image that has a smaller file size than a 12 megapixel image, it depends on the detail in the image and how it gets compressed.
03-10-2013, 04:44 PM   #4
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Both image size and quality as Anvh has already said, can dramatically alter file sizes.

03-10-2013, 05:06 PM   #5
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Original Poster
Thanks for the replies. It makes perfect sense when going back and looking at the photos again. The ducks were shot when there was a fresh snow and the pond was iced so most of the images contained a lot of white while the images of the baby have a lot of color through the whole frame. I will definitely be more wary of this moving forward. Thanks again.
03-10-2013, 07:03 PM   #6
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Just remember that LR lets you export however you want. I have presets setup for what I usually export to:
1024 on long edge
6 megapixels
10 megapixels
full size jpeg
499 pixels on long edge
And so on. Some are the same but they save to a different directory or rename a particular way as some sites require a naming convention, or I want them renamed so I know what the destination is. If you use a particular file size or image size very often then it is worth the time to set it up properly and then save it as a preset.

Presets are the key to using Lightroom, the program will quickly become tedious if you do everything manually. The first thing you should learn is how to create and save presets.

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