Summary > Color basics 7 / 10
 

"Assign profile" menu in Photoshop

 

Assigning an ICC profile to an image
Published on April 15, 2015 / Updated on October 21, 2018

 

"Assigning a profile" is a fundamental concept in color management because it is the beginning of the story of our photos...


Since there are more or less large color spaces, ICC profiles for each device, it is now necessary to know how to communicate the right color, the "same color" as much as possible, from one device to another, taking into account their characteristics or defects. Communication of the "right color" begins with assigning the right ICC profile to an image. Let's see why and how now...


 

 

Why is it necessary to assign an ICC profile or color space to an image ?


Essential ! This paragraph is one of the most important paragraphs of this site. A cornerstone !


Assigning an ICC profile or color space to an image allows it to display it correctly, quite simply ! The RGB values of the file will be "translated" by the "good" colors so the good colors L*a*b*. Let's look back at the history of an image file since the beginning of its history...

All cameras, even smartphones, can't take anything other than a RAW file. This one is therefore developed internally by a kind of mini-Photoshop in order to provide you with a nice JPEG file. The management of the colors of this photo and therefore the succession of the two fundamental stages of the history of a photo, i.e. "the assignment of a profile" and then "the conversion to a color space", is therefore done in a transparent manner for the user and automatically. Without color management no colors, even in a smartphone !

My RAW file is therefore a digital negative. On pro or some amateur cameras, you can retrieve this RAW file to develop it yourself in demo software such as Camera Raw or Lightroom. We will see below how it works then. But let's start with a smartphone or an amateur camera because they directly deliver a Jpeg file without any other possibilities. However, they will necessarily and above all take a photo in RAW format which will be developed internally by the internal mini-Photoshop in order to deliver your image in the form of the famous JPEG file.

 

Assigning an ICC profile or color space to an image allows it to display it correctly, quite simply !


So how does it work ?

In two steps, invariably... and according to this analogy with the story of a bank note ! You find a 100 something bill on the floor. It is a currency unknown to you. So you obviously can't use it in your favorite stores ! Two things will therefore have to be done : find out which country it comes from to give it a "universal" value and then convert it into dollars. This sequence "give it a value" then "convert" it is called in color management "assignment" then "conversion".

So first of all, we must give it meaning, find its country of origin to give it its universal value. OK, it's 100 things, so it's completely unusable in the United States ! In color management we would call this "The assignment of a profile". They must therefore be converted into dollars according to the exchange rate of the day, i.e. according to a universal value - let us assume gold. In color this standard is called the L*a*b* color space. This is called "conversion". The value 100 of the departure ticket is always 100 when it is identified as 100 something. When you give it meaning. In a photo, the assignment of an ICC profile does not change the RGB values of the file. Simply, RGB values are displayed "correctly" and no longer in a factual reading. Then we convert it into another currency, for example into dollars and they become 10 dollars - so with the same absolute value - my 100 have become 10. The L*a*b* colors are identical but the RGB values of the files are modified.

1 - JPEG photo case : assigning the camera's ICC profile to the image directly in the image

The "mini-Photoshop" of the camera must read the RGB values contained in the photo and translate them into the "right color" and therefore into its "ideal" L*a*b* colors. An RGB signal 255, 0, 0, 0 should be displayed with a red but with which red L*a*b*? This is done by reading the instructions in his ICC profile.
Let's say you took a picture of a perfectly grey wall. Your Jpeg photo should be perfectly grey at this point and therefore your file should have RGB values of style 128, 128, 128, 128. However, your camera has some defects and the RGB values recorded are more like 128, 138, 126. If you display these last values in Photoshop, you will see a greenish-yellowish grey instead. That's why you're disappointed ! But as the manufacturer of your device knows that it has these defects, it has calibrated it so it has noted its defects in its ICC profile i.e. in a table (a matrix table) where it has noted : I show you a neutral grey 128, 128,128 and you record 128, 138, 126 in the RAW file so with a dominant ugly color ! Thus the table tells him if you find an value RGB 128, 138, 126 you display a color L*a*b* 54, 0, 0, 0 therefore a value RGB 128, 128, 128, 128 and not a strange grey.

The RGB value of the file is correct and always 128, 138, 126 BUT the device acts as if it was 128, 128, 128, 128 at the time of its display. Assigning an ICC profile therefore serves only one purpose: to ensure that RGB values are correctly interpreted and therefore displayed without seeking to match RGB values with their "logical" display. An RGB value of 128, 138, 126 has no reason to display with a medium neutral grey without an ICC profile. An ICC profile does not transform a file. The RGB values of the RAW file remain the same but are then interpreted correctly. It's just an instruction manual, a post-it attached to the RAW file to tell it how to correctly display/view its RGB values.

The RGB value of the file is correct and always 128, 138, 126 BUT the device acts as if it was 128, 128, 128, 128 at the time of its display. Assigning an ICC profile therefore serves only one purpose: to ensure that RGB values are correctly interpreted and therefore displayed without seeking to match RGB values with their "logical" display. An RGB value of 128, 138, 126 has no reason to display with a medium neutral grey without an ICC profile. An ICC profile does not transform a file. The RGB values of the RAW file remain the same but are then interpreted correctly. It's just an instruction manual, a post-it attached to the RAW file to tell it how to correctly display/view its RGB values.

Then, it will be necessary to match the RGB values of the file and the display of the file. Indeed, the eye sees a beautiful neutral grey but if we place the Photoshop eyedropper tool on this grey, it shows us 128, 138, 126 !!!! It doesn't make sense ! This alignment is called conversion and we will see this in detail on the next page .

2 - Case of a RAW file processed by yourself

As I explain below on this page and on my pages dedicated to the color management in Camera Raw or Lightroom,

The ICC profile is also assigned automatically when you open your RAW file in the demo software. To display your photo "correctly", it has read the Exif data from the file, seen with which camera it was taken and has therefore assigned the ICC profile of this camera that belongs to its database - all cameras on the market pass through Adobe's hands and are calibrated by them to establish the ICC profile of each - to display the "right" colors so those that the box is supposed to have photographed and not those that are "logically" written in its RGB values (a 128, 138, 126 is displayed "as if" he had read 128, 128, 128, 128, 128 so with a beautiful grey without a dominant while the RGB value has a dominant).

3 - In the case of an image that comes from the Internet but does not have an ICC profile...

When you open it in Photoshop - this software manages colors so detects that there is no ICC profile attached to this photo or it needs it to correctly display this photo - Photoshop will suggest you to assign a profile to this image through a dedicated menu. It will therefore be sufficient to specify that the ICC profile of this image is probably the sRGB. We will review this in detail on the pages dedicated to the color management in Photoshop.

4 - Last precision - The "true" color: RGB values and L*a*b* color ?

Valeurs RVB identiques projetées dans l'espace LabIn order to properly represent why the same RGB value corresponds to a different real color - therefore L*a*b* - I projected four different color spaces or ICC profiles on the L*a*b* space. Opposite, we can see the upper right part (towards the red values) of this projection. The angle of each color space or ICC profile corresponds to the most saturated red value since having as RGB coordinates: 255, 0, 0, 0. However, we can see that this same color definition is not projected at the same place in the L*a*b* space, so it corresponds to different "real" red colors.

Note - If, on your screen, you have the feeling that these four red dots display the same shade of red, it is only due to the gamut of your screen which no longer allows you to distinguish distinct reds for such saturated colors).
The same RGB value (255, 0, 0, 0) and yet four real colours, so L*a*b* different in this example. To know which one, we just need to have the ICC profile or the color space associated with an image file for example and to assign it. The RGB value is then interpreted correctly and displayed with the red "good" L*a*b*.

5 - And by the way, what happens if you don't assign an ICC profile to an image ?

Without an ICC profile assigned to the image, it will be displayed arbitrarily according to two possible rules - because it cannot be otherwise - :

1 - In software that does not manage colors - It will simply appear in the color space of the screen quite simply differently on a screen displaying roughly the sRGB or Adobe RGB 98 as we see more and more often since the RGB values of the file are interpreted directly by the screen.
Example: If the image comes from an APN that was set in JPG and Adobe RGB 98 but the ICC profile has been lost and the image opens in Windows or Mac OS Explorer (which do not support color), the image will be displayed by default according to the color space of the screen (so still today most often in sRGB).

2 - In Photoshop if you don't enable your color management - which is the default case even if it may seem strange ! - There, the image will be assigned as an ICC profile the RGB workspace of Photoshop (sRGB by default).

top

 

 

How to assign an ICC profile to an image in Photoshop ?

We can say that there are two main cases :

Opening a "classic" image file in Jpeg, Tiff, PSD, etc...

''Assign profile'' menu in PhotoshopWhen you open a Jpeg, Tiff or Psd image without an ICC profile (i. e. without color space) in Photoshop (unlike a RAW file as we will see later), this one, if you have chosen to enable color management in this software (see Photoshop color preferences for more information and sample images), warns you and asks you to choose one. This is done either when the image is opened directly or, once the image is opened in Photoshop by the Edit menu / Assign profile...
Let's take an example with an image from my old scanner that I open in Photoshop correctly configured on my calibrated screen:
So I open this image - an IT 8 test chart - from my scanner (figure. a below). To understand this, I chose to open it without an ICC profile (figure a below left) - I did not assign the ICC profile of my scanner to the image opening - but as Photoshop necessarily needs to assign an ICC profile to an image to display it, it will force an assignment and in this case it will assign what is called its RGB workspace. Here the image opens in Adobe RGB 1998 since I had chosen this color space as my RGB workspace at the time. The image is displayed with arbitrary default colors, as if it were an Adobe RGB 1998 image. Each pixel contains RGB values that are interpreted in this workspace. In the image on the left below, you can see that the grey of the test pattern is reddish. Indeed, in the Adobe RGB 98 color space, the RGB value 98, 91, 87 are red. For my image to regain its "true" colors on the display, I must assign it the "right" profile, his! On the picture below on the right, I have assigned the profile of my scanner to my image and my grays regain all their neutrality! It's magical. And you will find that the RGB values are always the same. The RGB values of the info palette do not change BUT the displayed colors, the L*a*b* colors change ! Assigning an ICC profile only changes the display of a picture for given RGB values.

   
 
  The image to which the correct ICC profile has been assigned is simply displayed correctly, here on the right !
 

 

To do this, I used the "Image/Mode/Assign Profile" menu from Photoshop up to PS CS2 and the Edit Menu/Assign Profile for PS CS3 and later versions". Taking into account the characteristics (defects) of my scanner when reading its ICC profile, Photoshop now knows that for this device a signal 98, 91.87 should be displayed with a neutral color, a neutral gray and not a reddish gray. The image has also recovered a normal contrast.

My image now has an ICC profile that is dependent on my scanner and allows it to be displayed correctly taking into account its colorimetric characteristics. However, there is a big disadvantage !  There are no more matches between what I see and the "logical" RGB values. That's what we saw on the page - Dependent / independent profile -. For this to be the case again, I have to change the color space, so the ICC profile or more precisely here the color space since they are the only ones that are neutral. This is called a conversion and we will see on the next page what happens then... 

Opening a RAW file

In the case of RAW files, it is a little different and we can add that there are also two subcategories :

  • when RAW files are processed directly in the camera or smartphone (as we have seen above),
  • and when they are unmarked by us in dedicated software such as Photoshop's famous Camera Raw or its equivalent in Lightroom.

Choosing the color space on the camera: sRGB or Adobe RGB 98Please note that all cameras, even compact cameras or our smartphones can only take pictures in RAW format. They never take Jpeg directly even if the files that are saved on our memory cards are Jpeg files. In fact the RAW file is unmarked internally, with a "mini Photoshop" and therefore a "mini" Camera Raw, to deliver a Jpeg, more convenient for the vast majority of users. The procedure is then as follows: The RAW file is "opened" by the mini Photoshop installed in your device. To ensure that the colors are correct, the device assigns the correct ICC profile to the file, the one that the engineers have incorporated into their device. That makes sense ! Then, the same micro program converts the file into a neutral color space, in most cases, the famous sRGB (as we will see in more detail on the next page and as shown in the fig. above).

 

 
 

Choosing the color space sRGB or Adobe RGB 98 in the camera ?

First of all, this choice, which is made in the camera menus when the one that is starting to evolve a little bit, only applies to JPEG FILES ! If you choose RAW + JPEG on your camera, the sRGB or Adobe RGB 1998 color space will only apply to Jpeg files. The choice of the color space of the RAW files is made in the demo software and you choose it. This offers two advantages :
 You will have a choice,
 and most importantly, you will have more options. In Camera Raw it is for example possible to choose the large ProPhoto, sometimes useful in some cases ! 

To help you choose between sRGB and Adobe RVB 98 : My advice to choose your workspace  suivre

 
     

 

Remains the case that may interest us when we try to optimize the quality of the files that are taken by our cameras : the demosaicing of our Raw files by ourselves in a demosaicing software like the famous Camera Raw from Photoshop, Lightroom or even DXO and Capture One.

   
 

It is very clear that even the large DonRGB is much smaller than the L*a*b*. Today, itcorresponds substantially to the gamut of an inkjet printer on glossy paper.

 

In this case, the software MUST assign the camera's ICC profile when the file is opened automatically so that its colors are correctly displayed. To do this, these software has a complete database of all cameras on the market that are able to deliver RAW files with their ICC profile. By reading the EXIF data in the file, they know which device they were taken with and therefore how these devices "see" the colors. This is the reason why, when your software is not up to date, you cannot open the files of the most recent devices. Unable to assign them their ICC profile because it has not yet been created (the device has not yet been calibrated by Adobe), the software cannot open them. The big advantage of demo software is that it is possible in the next step, i.e. conversion to a neutral color space, to have other choices than the classic sRGB or Adobe RGB 1998.

   
  The next logical step is the conversion of a photo or more precisely the conversion of the RGB values of a photo into other R'V' B' values, corresponding to the same color L*a*b* : convert an image - 8 / 10 Suivre
   
 
 

To be remembered !


 What is a good color ? It is an L*a*b* color so it is an absolute color. An L*a*b* color corresponds to a single color.

 Assigning a profile is used to give a colorimetric meaning - a "true" color - to the RGB values of a photo. When assigning an ICC profile to an image, each RGB value (of each pixel for example) becomes the "correct" L*a*b* color. If you assign the right ICC profile to a photo, it will display the "right" colors, the ones they should have seen if the camera were perfect !
Imagine if you found a banknote of 100 or so things on the floor. This currency is unknown to you. You go to a bureau de change and the first thing the agent will do is to identify this note, give it meaning. Once you know what it is, you can request a conversion from that currency to your currency so that you can use it in trade. For a starting value of 100 you may only have 40 in your currency but it will have the same absolute value. For the colors it represents the same color L*a*b* but the RGB values are different !

 Assigning a profile therefore is used ONCE, at the very beginning of the history of this picture, for example in the camera or in Camera Raw if it is a RAW file. A $100 bill is worth $100. It is not worth 100 euros Then it will undergo many conversions in order to keep the same absolute value but this time in each currency....

 The assignment of the correct ICC profile for cameras is done automatically :
. Either directly in the body if you are shooting in Jpeg,
. or in your demo software such as DXO or Camera Raw.
If your device is new and you have not updated your software, so its camera database, you will simply not be able to open its RAW files because it will not be able to assign the right ICC profile due to a lack of profile! No profile = no "good" colors !

 The assignment of the correct ICC profile to an image downloaded from the Internet is done manually when it opens in Photoshop by assigning it the most likely color space, the sRGB.

 
     
  top
 
Through these 10 pages we will learn all the vocabulary related to color management : color spaces, ICC profiles, gamuts, etc...
 
- Introduction to color management
- Eye and color perception
- Colors and computer science
- Gamma
- Color spaces
- ICC profiles
- Assigning an ICC profile to an image - 7 / 10
  - Why do we need to assign an ICC profile ?
- How to assign an ICC profile ?
- To be remembered ...

- Convert an image
- Relative and Perceptual Conversion Modes
- What is calibration ?!

 

- 2018 monitors buying guide !
- My 13 full monitor review


 

Calibrate your monitor with the
best colorimeter: i1 Display Pro !

Read my Full review...

$244.78

Calibrate your photo printerwith the best quality/price ratio: i1 Studio !

Read my Full review...  

$489.00

   
 

 

     

 

 

 
 

 

       

From 2002, this Website offers...
 

This site dedicated to color management for photographers and videographers, beginners or professionals, visited by more than 328,000 people last year, offers on the one hand to help you easily understand and put into practice the color management of your photos and on the other hand helps you make the best investments with more than 70 hardware or software reviews since April 2002 in French and 2014 in English! It is the result of a patient work and a long experience shared by a professional but above all passionate photographer !

 

Where do the tested products come from ? Is my opinion completely independent ?

All the products I talk about on this site have been tested by me either following a personal purchase, a friendly loan, during a training session at a customer's site or after a manufacturer's loan. In any case, I decide what I want to test and even if, in the past, some brands were "disappointed" by my conclusions, things are moving today and my impartial opinion is more and more appreciated...

 

How is this site financed? What is my business ethics?

This site is largely free and yet without any product placement and without advertising. Why? But because I made a choice

 

fifteen years ago ! However, it must be recognized that it is lucrative and that it keeps many Internet sites alive.

So I asked myself the question : what can I do because this site can only grow with regular income, like the others ? How can I continue to make information accessible free of charge, which I have historically done since April 2002 ?


     


Thanks to affiliation : every time you click on the links on this site to my partner shops, they know that you come from me and give me a small percentage of what you buy : my buying advice or anything else. Remember to use my links when you buy from them ! So it costs you nothing and everyone wins : you, them, me ! And as I live in my time, I try to work as much as possible with sites that promote social ethics in their companies. In any case, I try to offer you a varied choice of possibilities to support me...

 

Legal informations

Legal information is available on my page Legal information - Contact me...

 
 

 

     

 

 

Top



 

Sitemap   |   About  Legal information