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Does saving a file in ProPhoto colorspace increase filesize? I'd think that given that it contains more informations it would use up more diskspace, (if so, how much more?) on the other hand, the number of pixels is the same, and if the color of a pixel is "Yellow" or "slightly brigher Yellow" should use up the same amount of space.

  • Why not just try a couple images? – Carl Witthoft Oct 3 '16 at 11:21
  • because i have my workspace set up for AdobeRGB, and because having it answered here, it could help other who have the same question. Beside that i COULD have found the answer myself, I do think that it is not a stupid question and Others can benefit from it. – sharkyenergy Oct 3 '16 at 11:26
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ProphotoRGB is the color space which defines the gamut. This RAW file size is controlled by the color depth (such as 14 bit). A 14 bit depth is the same size in AdobeRGB and ProphotoRGB. A jpg is 8 bit regardless of gamut chosen.

  • @sharkyenergy clear and compact, but not necessarily complete regarding JPEG images. Most of an image won't be using the colors in a wider gamut, meaning there will be fewer colors overall if you're using a limited 8-bit color space as JPEG does. An image will fewer colors should compress better resulting in a smaller file. You really should perform an experiment with some RAW conversions to different color spaces and see for yourself. – Mark Ransom Oct 4 '16 at 15:58
  • RAW is whatever data the sensor produces. You can't choose a color space for RAW. – szulat Oct 7 '16 at 14:45
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All other things being equal, saving file in ProPhoto instead of sRGB or AdobeRGB shouldn't increase the size. But ProPhoto files should be always saved in 16 bit color to avoid posterization. Compared to 8 bit workflow with sRGB the files are larger...

  • Thank you for pointing this out. I've seen some experiments in converting between sRGB and wider gamut spaces that are starting to come out like DCI-P3 and Rec. 2020, and you definitely want more than 8-bits per channel! – user1118321 Oct 4 '16 at 4:14
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An RGB image stores, for each pixel, an R value, a G value and a B value, which combine to define the colour of that pixel. Using 16 bits per channel (for example) allows for 281 trillion distinct colour possibilities for each pixel. This takes up the same amount of storage space regardless of the colour space of the image, whether it's sRGB, Adobe RGB, ProPhoto RGB or any other colour space.

The difference that the colour space makes is that wide-gamut colour spaces (such as ProPhoto RGB) encompass more real-world colours than narrower-gamut colour spaces; that is to say, 16-bit ProPhoto RGB images and 16-bit Adobe RGB images both have 281 trillion distinct colour values, but in the case of ProPhoto RGB, those colour values are "spread" wider to cover more real-world colours. (No colour space includes all real-world colours, but a wide-gamut colour space includes more of those colours.)

Let's say for example a pixel's (8-bit/channel) RGB value is (255, 253, 1). The difference in using one colour space over another is not in storage space, but in the fact that (255, 253, 1) will refer to a slightly different yellow in one colour space compared to the other. Or, to think of it the other way around, a wider-gamut colour space can encode a wider range of the yellows (or purples or whatever colour it might be) that are out there in the real world.

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