Why doesn’t changing DPI in Lightroom make an exported JPEG larger?
Asked 12/18/2017
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2 answers
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I exported a 6000×4000 RAW photo from Lightroom as a JPEG at Quality 100. With the export set to 240 DPI, the file was about 12 MB. Exporting the same image at 600 DPI produced essentially the same file size. I expected a higher DPI setting to create a larger file. Why doesn’t it?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
8y ago
2 Answers
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An image doesn't have a DPI until you print it.
All it has are dimensions in pixels.
Anything else is simply an interpolation of one system to another in order to display on your screen... which is probably about 72dpi anyway.
If your image is 6000 x 4000 pixels, then that's its size, whatever dpi you think you may have saved it at.
The only time DPI comes into play on your computer is if you paste into any word processor or page layout app, when the DPI is used to decide how large the image will be when printed.
(extrapolation of my post at https://photo.stackexchange.com/a/93405/57929)
Originally by user57929. Source · Licensed CC BY-SA 4.0
user57929
8y ago
0
Generated from our catalog & community — verify before relying on it.
Because changing DPI does not add pixels to the image. Your exported photo is still 6000×4000 pixels either way, so the amount of image data is essentially the same.
The DPI/PPI value stored in the file is mainly metadata: it tells print or layout software how large to print the image. For example, a 6000×4000 image prints at about 25×16.7 inches at 240 DPI, or about 10×6.7 inches at 600 DPI. Same pixels, different print size.
JPEG file size is driven mostly by pixel dimensions, image content, and compression/quality settings—not the DPI number alone. So if quality and pixel dimensions stay the same, the file size will usually stay about the same too.
If you want a smaller exported file, reduce the pixel dimensions by resizing/resampling the image, or lower the JPEG quality setting.
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