Converting RAW to JPG

Started Dec 4, 2012 | Discussions thread
JJMacks Forum Pro • Posts: 10,432
Re: Converting RAW to JPG

Brian wrote:

I have just started shooting in RAW and I took a picture, that has a file size of 16.8mb, and converted it to JPEG in both my new Lightroom software and the IrfanView freeware I have. The file size via LR dropped to 10.3mb and 5.53mb for IrfanView.

All those file sizes are correct for you can use the all files. So they are good files not corrupt.

The file sizes has to do with the files contents and quality. RAW files contains your camera's meta data, your cameras RAW sensor data and an embedded jpeg image. Compression may be used on the raw data as well as the jpeg image. So the size of you cameras RAW files will vary in size.

Jpeg files do not contain you cameras sensors RAW data. They just contain metadata and a RGB image. Jpeg files use a lossy compression when you encode(save) your image into a Jpeg format image file. When you decode a Jpeg file it does not decode the compressed data to exactly the same image that was encoded there is some quality loss. A jpeg file will always decode the same way to the same decoded image. Because compression is used Jpeg file sizes at any give quality will vary in size depending on image content and detail.

During jpeg encoding a quality value is uses that influences the compression a value 0 to 12. Using a low value will produce a smaller file at the expense of reduced image quality. As far as image quality goes you not going to see a big difference between quality 10 and quality 12. However the quality 10 file size is quite a bit smaller then the quality 12 file size. I think most cameras use quality 10 for their cameras high quality jpeg image sizes.

When you encode decode encode decode etc you accumulate image quality loss. However. If you convert a RAW file into a RGB image and the save it 100 time during Post processing its the same as doing on doing one. You only accumulate the quality loss when you go through the process of decoding an encoded image process it some then encode a new image. If you decode once ans save 100 time its the same as doing one encode save. Generation degrade. All in a generation have the same quality as long as the same quality setting is used for each save.

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