Why does Canon Digital Lens Optimizer make a CR2 file much larger?
Asked 3/1/2013
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In Canon Digital Photo Professional, enabling Digital Lens Optimizer (DLO) on a CR2 RAW file can make the file nearly double in size. If DLO is later unchecked, the file size drops back to normal. Why does applying DLO increase the RAW file size so much?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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Digital Photo Professional writes additional information for the DLO processing to the RAW image; the result is that the RAW image file will increase in size, often significantly.
It saves not only the new corrected image in RAW format but also the original image into the file - or at least the steps taken to get from the original to the corrected version. The issue is that the Cr2 file has to be still readable by other RAW format capable software to read the corrected image, but still preserve the old image for a reversal of the process.
Originally by user9441. Source · Licensed CC BY-SA 4.0
user9441
13y ago
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Generated from our catalog & community — verify before relying on it.
Because DPP is writing extra data into the CR2 file for the Digital Lens Optimizer adjustment. Canon states that DLO adds additional processing information to the RAW image, which can increase file size substantially.
In practice, the file is not simply being replaced with a smaller corrected version. DPP needs to preserve the original RAW data while also storing the information required for the DLO-corrected result, or the steps needed to recreate it. That lets the edit remain reversible inside DPP.
A likely reason the file grows so much is compatibility: the CR2 still needs to remain a readable RAW file for software that supports the format, while Canon’s own software can also recognize and reverse the DLO adjustment. So the larger size comes from the added correction metadata and/or stored correction data, not from any mysterious change to the sensor capture itself.
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