File sizes seem small when exporting from Lightroom

I followed lots of online guides to make sure the photos were good. But when i export them to Jpeg the file sizes seem small like 3MB


does that seem normal? thanks

Yes, that's normal.

Due to JPEG compression, megapixels won't directly translate to megabytes.

Concern yourself primarily with pixel dimensions (width/height such as 3600x2400), secondarily with output jpeg compression and output sharpening.

Here's a good read that's related to this subject:
http://regex.info …room-goodies/jpeg-quality

It depends what you're working with. I've got two that I recently exported for prints; both are 3648x5472, one is 28.1 MB, the other is 14.3 MB. Mine are both exported from raw files, not sure if that makes a difference.

KLR-VA0501 wrote in post #18064892
It depends what you're working with. I've got two that I recently exported for prints; both are 3648x5472, one is 28.1 MB, the other is 14.3 MB. Mine are both exported from raw files, not sure if that makes a difference.

A 20 MP image, which in 8 bits and uncompressed makes a file of around 57 MB, and after Jpg compression is 28 MB? That is compression of only 2:1, possibly the minimum compression that the Jpg format is capable of. Are you setting the LR Quality slider to 94 - 100? That is not the most efficient use of Jpg - perhaps you should read the article linked above by Nathan.

Note that 100% (LR) and Q12 (PS) is unnecessary for most things. Q10 is more than enough for printing, and prints from a Q8 file will look exactly the same.

A 30MP image that's mostly blue sky will be very small, maybe less than a 1MB. On the other hand a photo of something with detail, like trees, will be quite large, many MB, possibly over 10MB with a high MP camera. From my 12MP camera most images for customers are between 1MB and 4MB, and you can print a billboard from them.

I downloaded the test exporter that was used in the linked article, and ran some tests of my own. Not only is the Q10/80 setting visually indistinguishable from the 8 bit TIFF file, but if you load all of the images that are generated in to PS as layers in one document, and set the blend modes to Difference it is virtually impossible to measure the per channel differences in any particular channel. The Thread i created about it may be found here. Since I ran this test I have always used Q10/80 as my default maximum quality output, even for printing.

Alan

After reading the article and exporting the same 28.1 MB file with settings of 85 and 75, I see no difference in the image when viewing; same pixel dimensions but the overall size of the file went down to 13.8 and 10.3 for the lower settings. No discernible difference in image quality while reducing the file size considerably. Not sure what I'll use for my default but I'll probably go back to the default setting of 75 but at the same time keep close tabs on the output quality of the images.

KLR-VA0501 wrote in post #18067673
After reading the article and exporting the same 28.1 MB file with settings of 85 and 75, I see no difference in the image when viewing; same pixel dimensions but the overall size of the file went down to 13.8 and 10.3 for the lower settings. No discernible difference in image quality while reducing the file size considerably. Not sure what I'll use for my default but I'll probably go back to the default setting of 75 but at the same time keep close tabs on the output quality of the images.

When you change Quality in the output of JPG files, what you are affecting is the amount of data compression of the file...which is accomplished by 'binning' similar colors more finely or coarsely. Those changes might nor might not be perceptible to your eye, if you look in 'same color' areas like large expanses of sky. For example

• ...if the reality is that there are ten shades of 'sky blue' in the sky, quality 10 preserves all ten, while quality 7 might preserve eight of them and quality 8 preserves 9 of them
  
• ...if the reality is that there are one hundred shades of 'sky blue' in the sky, quality 10 preserves all one hundred, while quality 7 might preserve 70 of them and quality 8 preserves 85 of them
  

I just did a quick test using an image from a Canon 40D using LR3 to output native resolution images (3888 x 2592) ...

1. quality 100 = 7.57 MB
   
2. quality 90 = 4.9 MB
   
3. quality 80 = 3.41 MB
   
4. quality 70 = 2.49 MB
   
5. quality 60 = 1.36 MB
   
6. quality 50 = 1.2 MB