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

>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

"C Wright" <wright9_nojunk@nojunk_mac.com> wrote in message
news:BFD959F0.4DDF6%wright9_nojunk@nojunk_mac.com...
>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

> 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

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.

On 12/29/05 11:05 AM, in article
1135875938.813565.294570@g44g2000cwa.googlegroups.com, "Bill Hilton"
<bhilton665@aol.com> wrote:
 
>
> 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