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Author Topic: Converting 16 bit to 8 bit  (Read 1932 times)
texshooter
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« on: June 19, 2013, 06:29:29 PM »
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If I convert an image from 16bit prophoto to 8bit prophoto, will I see any loss in quality or color accuracy? I'm thinking NO because I haven't changed the color space (prohoto). I understand that 16 bits is better for image capture (camera) and image editing (Photoshop), but what about image printing? Let's say I finished editing my 16bit Prophoto image and I'm happy with the colors and tonality. Now it's time to send that image file to my photo lab for printing. They insist that I send them the file in 8bit only. OK, no prob. I convert the 16bit Prophoto to 8 bit Prophoto. Because i already finished the editing phase, I have no need to stretch tone curves, bend pixels, or do any color manipulation whatsoever, so I don't need a 16bit channel anymore. So converting to 8 bits only reduces the file size; it has no effect on color or dynamic range, correct?
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Slobodan Blagojevic
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« Reply #1 on: June 19, 2013, 06:47:33 PM »
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Well, I am sure those more experienced and knowledgable will chime in, but in the meantime, here is what I think: the weak link in your reasoning seems to be the ProPhoto color space. Since I am not aware of a lab that will print it in ProPhoto, there must be a conversion to the printer/paper space at some point. Since your file is already in 8 bits, the conversion would happen there as well. I think you would be better off converting to the lab's profile (which could be even sRGB) while you are still in 16 bits.
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Slobodan

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FranciscoDisilvestro
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« Reply #2 on: June 19, 2013, 07:35:53 PM »
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The possible issues with 8 bits and ProPhoto RGB are not related to dynamic range or color, but banding, especially in the shadows. Now, if you are done with the editings this risk is low.

I agree with Slobodan about converting to the printer color space. If they are requesting 8 bits, then they might also have specifications about color space (how do you softproof without it?). Converting to the final profile has also the advantage that you can select the rendering intent according to your taste.

In any case, make sure they handle properly a file in ProPhotoRGB
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Rhossydd
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« Reply #3 on: June 20, 2013, 01:09:48 AM »
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"Seeing" the difference between 16 and 8 bit print image is marginal, but only possible if you're printing to one Canon's 16 bit printers anyway.

Converting from 16 bit to 8bit, in theory, could cause some colours to shift very slightly, but other factors will make that theoretical change not worth worrying about. The repeatability of printers is a greater source of errors.

Maybe a more important issue is what printer they are using(and can you get hold a profile for it to soft proof with) and can they actually handle a ProPhoto file correctly anyway ?
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BartvanderWolf
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« Reply #4 on: June 20, 2013, 02:15:29 AM »
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The possible issues with 8 bits and ProPhoto RGB are not related to dynamic range or color, but banding, especially in the shadows. Now, if you are done with the editings this risk is low.

I agree with Slobodan about converting to the printer color space. If they are requesting 8 bits, then they might also have specifications about color space (how do you softproof without it?). Converting to the final profile has also the advantage that you can select the rendering intent according to your taste.

In any case, make sure they handle properly a file in ProPhotoRGB

Yes, I fully agree with Slobodan and Francisco. If possible, use their recommended output profile for proofing and converting to that profile while in 16-bit/channel. Only then, also after resampling to output PPI and output sharpening, change the mode to 8-bit/channel for the final print file (which may then as well be a high quality JPEG, since no further image processing of any major significance is to be expected).

Cheers,
Bart
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