![]() ![]() It still isn't lossless and simplification still occurs, but the level of simplification can very from one program to another. EXPORT DARKTABLE PLUSThat, plus the overhead of the JPEG file format can result in a larger overall file than the original RAW potentially.Īs far as different sizes for max quality between encoders, that's simply a result of the difference between values used when encoding "100%". The RAW file on the other hand is likely using a general purpose lossless compression that looks finds patterns that the JPEG encoder isn't finding. While JPEG is great at reducing file size by allowing images to be simplified in subtle ways, it's a one trick pony that doesn't look for patterns across the entire image that would allow for the size to be reduced losslessly. However, comparing it to a RAW file can be a bit misleading since a RAW file would need several steps (including a step called demosaicing, which will increase size due to interpolation) to expand it out to a proper uncompressed bitmap image.ĭifferent encoders use different values for the maximum quality. Note that the JPEG image will never be larger in size than the uncompressed bitmap image, for any normal image. In others it might not necessarily go that far, or it may (as mentioned above) affect other aspects of the encoding such as the chroma sub-sampling. In some it means to use the lowest quantizers available (preserving the most detail). Under the hood, it's these quantizer values that actually affect the quality, and you can't usually adjust these directly.Įven the "100%" quality setting can mean different things between encoders. ![]() The quality settings is only indirectly influencing the algorithm that the encoder uses to choose quantizer values for each block in the image. Different JPEG encoders will apply different meanings to the quality setting, so you can't compare quality settings between different encoders.įor example, 80% quality in one encoder may choose similar average quantizer values to 92% quality in another encoder. And some may not allow any adjustment to this setting at all.ĭifferences between how encoders interpret the quality setting. Some may use a different, separate control to the quality setting. Chroma sub-sampling in JPEGs reduces the spatial resolution of the chroma channels in return for reducing the file size with little noticeable different in quality, at least of most photographic material.ĭifferent JPEG encoders may adjust the chroma sub-sampling differently: some may adjust it along with the quality setting, so a higher quality will also use less sub-sampling. The discrepancy in size between JPEGs encoded at "100% quality" in different encoders is likely to be a result of one of the following:ĭifferent chroma sub-sampling setting. For your 24MP images you will probably hit that limit at around 1.5Mb, whichever the jpeg quality number that may be in your program. So you should take an image with a lot of details and a clear sky, and save then at 100, 90,80,70,60,50, until you can see a quality hit. So it seems like overkill that your 100% is barely compressing at all. And flipping between the 4Mb and the 950k file at 100% zoom, I can see no difference. With the JPEGLIB that I use for my jpeg handling a 16MP image becomes 4Mb, and it quickly goes down to 1.7Mb at 95, at no perceivable quality hit. The jpeg quality numbers are arbitrary - all you know for sure is that quality 100 is larger than 90, and 90 is larger than 80 in the same program. This means that if you set the compression to be very gentle, it can easily still be larger than the raw. It is the uncompressed bitmap size that is the base size for the compression to work its way down from, not the raw size. Now to the point, since we are talking about jpegs here. So you can expect an uncompressed 16bit RGB "bitmap" to be approaching 3 times larger than the raw, and times 3 divided by 2 for 8bit uncompressed. ![]() EXPORT DARKTABLE FULLNikon NEFs store full res previews while Canon uses half res, hence the larger fraction. Uncompressed RGB files (3 values per pixel) will be larger than your raws, as the raws contain a monochrome bitmap (1 value per pixel), and usually a downscaled, aggressively compressed preview that takes a fraction of the size, 400k for Canon 10MP cameras, and 1M for Nikon D5100 (I know these numbers because I used to read them out of the raw files and store them in a temporary file). ![]()
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