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Frequency Seps and profile conversions

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  #11  
Old 06-29-2010, 02:32 PM
Flashtones Flashtones is online now
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Re: Frequency Seps and profile conversions

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Originally Posted by andrewrodney View Post
No, not necessarily. That’s an extreme case. Anytime you alter pixel values, there are rounding errors and thus data loss. The cases above fall into this camp. This can be compounded by many such edits until as you point out, the histogram shows this and eventually, it shows upon output.

The real question should be, why does one need to assign the profile to this set of numbers? Why is the original tag not the proper tag?
Because, (on your advice) I'm editing an image in ProPhoto with colors that roughly enough could fit into sRGB, and I need to downsize to 8-bit to reduce overhead. My understanding, again from you, is that Prophoto is an inappropriately large a space to edit closely spaced tones in 8-bit.

Web will be the primary use.

Thus, I tried to do the color space conversion first, in 16-bit, to reduce rounding errors, but the result is unusable. However, I was able to get a usable result by first assigning the profile, then converting, then downsampling. All this is explained in my first couple of posts.

Of course all this is done on a copy and I still have the 16-bit ProPhoto version archived. I simply needed to reduce overhead as the file size grew untenable, and the remaining edits are minor.
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  #12  
Old 06-29-2010, 02:35 PM
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Re: Frequency Seps and profile conversions

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Originally Posted by Flashtones View Post
Because, (on your advice) I'm editing an image in ProPhoto with colors that roughly enough could fit into sRGB, and I need to downsize to 8-bit to reduce overhead. My understanding, again from you, is that Prophoto is an inappropriately large a space to edit closely spaced tones in 8-bit.
If the image is in ProPhoto, you are assigning sRGB? You want to be converting to sRGB.

Assign Profile is to tell Photoshop the true scale (color space) of the numbers. I assume you have a true ProPhoto RGB document and you like its color appearance. Now you want to make a copy in sRGB for the web. You would use the Convert to Profile command (or Save for Web). Assign profile should make the image look awful (unless the original assignment was wrong).
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  #13  
Old 06-29-2010, 03:04 PM
Flashtones Flashtones is online now
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Re: Frequency Seps and profile conversions

You're just not reading what I write.
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  #14  
Old 06-29-2010, 03:08 PM
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andrewrodney andrewrodney is offline
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Re: Frequency Seps and profile conversions

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Originally Posted by Flashtones View Post
You're just not reading what I write.
You wrote:

Quote:
I was able to come to a satisfactory solution by assigning the profile before converting to it
There is zero reason to be doing this.
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  #15  
Old 06-29-2010, 03:22 PM
Flashtones Flashtones is online now
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Re: Frequency Seps and profile conversions

I also wrote several times that converting directly yielded an unusable image. Some layers/blend modes are converting differently than others.

I appreciate that you're trying to help. I understand there might be something outside the norm with this file. Maybe in a day or two I can post an example.
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  #16  
Old 06-29-2010, 03:35 PM
Flashtones Flashtones is online now
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Re: Frequency Seps and profile conversions

Andrew, if converting to profile doesn't affect some layers differently than others, why is there a checkbox to flatten to preserve appearance?

Under what circumstances would flattening help, or conversely, would not flattening be detrimental? Are there instances where the preview in the convert dialog box is not indicative of results?

Mind you, I did allow it to rasterize smart objects.
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  #17  
Old 06-29-2010, 04:28 PM
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Re: Frequency Seps and profile conversions

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Originally Posted by Flashtones View Post
Andrew, if converting to profile doesn't affect some layers differently than others, why is there a checkbox to flatten to preserve appearance?
Depending on the blend modes, a conversion absolutely can change the color appearance. There have been color differences observed, again depending on the layer stack and blends modes, just from flattening a document. No need to even convert to see this.

The bottom line however is this. If you assign a profile to a document and convert it, you’ll get a different conversion (resulting numbers) than if you didn’t assign that profile prior to the conversion. As I said above, the only reason you assign a profile is if the current assignment is incorrect. Hence the question, why are you assigning that profile in the first place?
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  #18  
Old 06-29-2010, 04:31 PM
mushmush mushmush is offline
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Re: Frequency Seps and profile conversions

Adjustment layers, blending modes and transparencies will change (some more perceptively than others) - when converting profiles. There is also the difference in gamut- colors available- between color spaces.
The option to flatten to preserve appearance should take care of the everything but the possibility of a gamut issue. The great negative to flattening is you are then unable to tinker with your layers.
ALWAYS- ALWAYS "save as" a new name file after flattening. You may then be able to use selections from the layered file on your flattened by cut and pasting.
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