JPG quality and file sizes

26-Oct-2009 00:00 | Comments: 0 | Categories:

When you Export from Lightroom and select the JPG quality it seems to use a different scale from other software.

Even setting it to 50 makes a very big file, which if I open and resave in Irfan reduces from 170 to 110 (quality 70%) (and 356 to 190).  Not sure how safe it is to reduce the LR quality factor - or maybe it just generates big files.

I want a small file size because in my gallery, click on a single image and you get the large image on the screen.  Smaller file sizes download faster.

No obvious answers - but see this for loads to flickr, which seems to resize anyway.

I'm going to do some tests with export a single image.

Export to 1024 pixels longest edge.

Chose an image which generated a file size which was very big because it has a lot of detail – leaves etc.  Even at 5 no obvious jpg artifacts.

LR JPG quality          File size (Kbytes)    Open in Irfan and save-for-web, quality 70, file size

100                               1266                          192

90                                 952                           192

80                                 726                           192

70                                 559                           192

60                                 362                           191

50                                 356                           191

40                                 308                           188

30                                 244                           171

20                                 196                           138

10                                 167                           117

05                                 158                           111

Now another image

5                                  53                             bad artifacts

10                                 55                             bad artifacts

20                                 60                             less artifacts

30                                 73                             almost no artifacts

40                                 88                             51 (LR image clean, Irfan makes artifacts)

50                                 101                           56 (Irfan artifacts only visible when enlarging)

 

100                               428                           53 (Irfan artifacts only visible when enlarging)

I see the Lightroom Preset Export Option ‘Export for Email’ uses quality of 50.  Looking at the data above, I suspect you’d be safe with 40, but still will end up with bloated file sizes.

Alternatively, and a bit of an extra step, export at a highish quality (say 60), and then use Irfan to blast through and resize them (say 70).

 



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