Assign Profile vs. Convert to Profile?

CW
Posted By
C Wright
Dec 29, 2005
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557
Replies
5
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Closed
I am a bit confused regarding the appropriate use of the ‘Assign to Profile’ versus the ‘Convert to Profile’ functions on the Photoshop Edit menu. I think that I understand the basic differences in function, that is the ‘Assign’ command simply assigns a different color space with out actually converting any colors to to different numerical values within the new color space. While the ‘Convert’ command actually converts colors to different numerical values in the new color space. But, when is it appropriate to use one command over the other?

If, for example, I am preparing an image edited in the Adobe RGB color space, for the web or for a lab, where sRGB is required is it not necessary to use the convert function? Will the assign function work equally well?

It would appear obvious that conversions to radically different color spaces would require the use of the convert function. But, if the assign function would not even be appropriate for less radical conversions like aRGB to sRGB then what is it for?
Chuck

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BH
Bill Hilton
Dec 29, 2005
C Wright wrights …

I am a bit confused regarding the appropriate use of the ‘Assign to Profile’ versus the ‘Convert to Profile’ functions on the Photoshop Edit menu.

I think everyone has problems with this at first …

I think that I understand the basic differences in function, that is the ‘Assign’ command simply assigns a different color space with out actually converting any colors to to different numerical values within the new color space. While the ‘Convert’ command actually converts colors to different numerical values in the new color space.

You got it …

But, when is it appropriate to use one command over the other?

I have a friend who is struggling to learn this as well so I put together two jpegs as teaching aids, feel free to download them and make the assignments when you open them in Photoshop to see the differences … basically I converted a RAW file in ‘ProPhoto’ working space, which has a very wide gamut, and marked off an area of bright red that I measure as 144/89/46 … then I converted a copy to sRGB in preparation for ‘save for web’ and when I convert the red area becomes something like 200/77/39 in sRGB … then I made jpegs of both files using ‘save for web’, which drops off both working space profiles.

When you view these on the web in a non-color managed browser the sRGB version looks pretty close to right since that’s what sRGB was designed for, but the ProPhoto version looks dull because 144/89/46 means "RED" in ProPhoto space but "blah crappy red" without the profile. You can download both of these and then open them in Photoshop and assign different working spaces each time you open one and see the effect this has, but basically if you assign ‘ProPhoto’ as working space to the 144/89/46 one it looks good, as does assigning ‘sRGB’ to the already converted one. Here are the files if you want to look and try this … http://members.aol.com/bhilton665/hilton_srgb.jpg
http://members.aol.com/bhilton665/hilton_prophoto.jpg

Hope this helps …

If, for example, I am preparing an image edited in the Adobe RGB color space, for the web or for a lab, where sRGB is required is it not necessary to use the convert function?

I would *always* convert when going from AdobeRGB to sRGB since the numeric values mean different colors. The example I used is more extreme because ProPhoto is a wider space (so saturated "red" has lower RGB values) but you’ll still see something similar to what my examples show, especially with saturated colors … it won’t be as obvious but you’ll typically see a difference. In a few minutes I’ll put up the AdobeRGB version if you wish, it should be somewhere between the ProPhoto and sRGB versions though.

It would appear obvious that conversions to radically different color spaces would require the use of the convert function.

Yes, this is what my ProPhoto example was meant to show …

But, if the assign function would not even be appropriate for less radical conversions like aRGB to sRGB then what is it for?

I stumbled over this when I was making web images of landscape photos of the "red rock country" in the desert southwest … I was selling prints so needed the web images to look as similar to the print images as possible and taking Ektaspace or AdobeRGB files directly to the web would often kill the colors, so I eventually figured out why. So my final point would be that for some colors you won’t see much of a difference if you convert AdobeRGB files directly using ‘save for web’, but with reds and oranges and some other saturated colors you’ll see a big change compared to first dumbing them down to sRGB … so I just always do the conversion to sRGB now before running ‘save for web’.

Bill
MR
Mike Russell
Dec 29, 2005
"C Wright" wrote in message
I am a bit confused regarding the appropriate use of the ‘Assign to Profile’
versus the ‘Convert to Profile’ functions on the Photoshop Edit menu. I think that I understand the basic differences in function, that is the ‘Assign’ command simply assigns a different color space with out actually converting any colors to to different numerical values within the new color
space. While the ‘Convert’ command actually converts colors to different numerical values in the new color space. But, when is it appropriate to use
one command over the other?

The rule of thumb is this: "convert" is used when you want to preserve the appearance of the image, and "assign" is used when you want to change the appearance of the image.

If, for example, I am preparing an image edited in the Adobe RGB color space, for the web or for a lab, where sRGB is required is it not necessary
to use the convert function? Will the assign function work equally well?

You would use convert. If you assign sRGB to an Adobe RGB image, the colors will be less saturated.

It would appear obvious that conversions to radically different color spaces
would require the use of the convert function. But, if the assign function
would not even be appropriate for less radical conversions like aRGB to sRGB
then what is it for?

Probably the most common use of the assign function is to compensate for someone else’s error or omission . There are other uses. For example, an easy way to bump overall saturation is to convert to sRGB, and then assign Adobe RGB or even ProPhoto RGB.

There are other uses, again involving changing the appearance of the image as part of a color editing operation. Profile assignment is an effective way to manipulate certain images. An operation called "pseudo profiling" can be very effective in rescuing very underexposed images. In this procedure, a "pseudo profile" is created by modifying Adobe RGB with a very high gamma value of 20 or so. When this is assigned to an underexposed image, the color and contrast can be boosted significantly. This technique was introduced, AFAIK, by Dan Margulis, and appears in his latest Professional Photoshop book.


Mike Russell
www.curvemeister.com
BH
Bill Hilton
Dec 29, 2005
I wrote …

In a few minutes I’ll put up the AdobeRGB version if you wish, it should be somewhere between the ProPhoto and sRGB
versions though.

http://members.aol.com/bhilton665/hilton_adobergb.jpg … so if you download this one and assign the right profile when you open it then it will look correct … if you open all three of these at once in a web browser you can see the difference between dropping the ICC profiles for different gamut ‘working spaces’.

Bill
GC
Graeme Cogger
Dec 29, 2005
I agree with everything stated previously 🙂

One more common use for ‘assign profile’ is if you’ve had a custom profile made for an input device (scanner or camera). In this case, the image will probably arrive at your computer in sRGB (or sometimes AdobeRGB), so you assign the correct device profile. The original profile is approximate interpretation of the RGB values, but by assigning the device profile you are interpreting the values more accurately.
CW
C Wright
Dec 29, 2005
On 12/29/05 11:05 AM, in article
, "Bill Hilton"
wrote:

I wrote …

In a few minutes I’ll put up the AdobeRGB version if you wish, it should be somewhere between the ProPhoto and sRGB
versions though.

http://members.aol.com/bhilton665/hilton_adobergb.jpg … so if you download this one and assign the right profile when you open it then it will look correct … if you open all three of these at once in a web browser you can see the difference between dropping the ICC profiles for different gamut ‘working spaces’.

Bill
Thanks to all for the very clear answers. And, Bill, I downloaded all three images that you posted and played with the profiles; the the changes do indeed make some pretty dramatic differences – thanks!
Chuck

Must-have mockup pack for every graphic designer 🔥🔥🔥

Easy-to-use drag-n-drop Photoshop scene creator with more than 2800 items.

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