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