6 Replies Latest reply: Jan 11, 2014 7:14 PM by zaki mohammed reda RSS

    .ACO swatch file

    zaki mohammed reda Community Member

      Hi all,

      I am trying to understand how the .ACO color files store color swatches. More precisely, I want to know what does a Pantone color swatch file includes as data ? and how the two color representations (PMS and L*a*b*) are plugged ?
      Thank you so much in advance,

        • 2. Re: .ACO swatch file
          zaki mohammed reda Community Member

          Thank you so much Mr Hoffmann for you help !
          Sincerly, I still don't understand how the Pantone spot colors can be converted to other color spaces such as CMYK, RGB..

          Do these ACO files contain the whole data or does Photoshop convert the colors ??

          • 3. Re: .ACO swatch file
            G.Hoffmann Community Member

            I don't have practical experience using ACO or ASE programatically, but we can try to investigate the issue:

             

            Reference (2) says:

             

            ---quote

            OS

            Filetype/extension

            Mac OS

            8BCO

            Windows

            .ACO

             

             

             

            Color swatches file format

            Length

            Description

            2

            Version ( =1 )

            2

            Count of colors in the file.

            count *10

            Colors. Each color is 10 bytes, as described in See Color structure.

            At the end of a version 1 file is the version 2 information.

            2

            Version ( = 2 )

            2

            Count of colors in the file. The next two fields are repeated for each count.

            count *10

            Colors. Each color is 10 bytes, as described in See Color structure.

            Variable

            Unicode string: color name.

             

            Color structure

            Length

            Description

            2

            The color space the color belongs to (see See Color space IDs).

            8

            Four short  unsigned integers with the actual color data. If the color does not  require four values, the extra values are undefined and should be  written as zeros.

            See See Color space IDs.

             

            Color space IDs

            Color ID

            Description

            0

            RGB.

            The first three values in the color data are red , green , and blue . They are full unsigned 16-bit values as in Apple's RGBColor data structure.

            Pure red = 65535, 0, 0.

            1

            HSB.

            The first three values in the color data are hue , saturation , and brightness . They are full unsigned 16-bit values as in Apple's HSVColor data structure.

            Pure red = 0,65535, 65535.

            2

            CMYK.

            The four values in the color data are cyan , magenta , yellow , and black . They are full unsigned 16-bit values.

            0 = 100% ink. For example, pure cyan = 0,65535,65535,65535.

            7

            Lab.

            The first three values in the color data are lightness , a chrominance , and b chrominance .

            Lightness is a 16-bit value from  0...10000. Chrominance components are each 16-bit values from  -12800...12700. Gray values are represented by

            chrominance components of  0. Pure white = 10000,0,0.

            8

            Grayscale.

            The first value in the color data is the gray value, from 0...10000.

             

             

            Photoshop allows the specification of custom  colors, such as those colors that are defined in a set of custom inks  provided by a printing ink manufacturer.

            These colors can be stored in  the Colors palette and streamed to and from load files. The details of a  custom color's color data fields are not public and

            should be treated  as a black box.

            -----end of quote

             

            We have one of five color spaces (the color space belongs to...): RGB, HSB, CMYK, Lab, Grayscale.

            Lab is device independent (and without further information based on the CIE-Standard-Observer (2°) and Reference Illuminant D50).

            Conversions between color spaces require an ICC profile or a Tone Reproduction Curve for Grayscale (Gamma, Dot Gain).

            I don't think, that a specific profile is embedded (there is no information available about).

             

            Pantone spot colors (as available in Photoshop) are based on Lab values. The conversion into an RGB space uses the specific

            RGB ICC-profile for sRGB, Adobe RGB, ProPhoto  etc.  HSB is just another coordinate system for the respective RGB space.

            the conversion into a CMYK space is based on the specific CMYK ICC profile. Correct results can be achieved, if the actual

            printing process reflects really the intended proces, like ISOCoated_v2_eci or SWOP. Given CMYK numbers for Pantone spot

            inks are almost useless – the CMYK space is mostly undefined and many spots are out of gamut.

             

             

            I'm sure you'll get much help here or in the Photoshop Forum, If you specify your practival problem.

             

            Best regards -Gernot Hoffmann

            • 4. Re: .ACO swatch file
              zaki mohammed reda Community Member

              Thank you pretty much again Mr Hoffmann for your prescious help !
              Concerning my practical problem, I am trying to investigate an experimental procedure whereby I can define transparent colored jewels' colors in PMS (Pantone Matching System).
              Therefore, I have to inquire about the different suitable instruments to measure the transparent colored samples' colors in L*a*b* system, and then to search all the existing ways to convert L*a*b* color coordinates to nearest Pantone colors.
              Again, thank you so much for you help !
              Kind regards,

              • 5. Re: .ACO swatch file
                G.Hoffmann Community Member

                One method, how to find the nearest Pantone color for a given color in Lab, using Photoshop:

                 

                For PS CS2 / old Pantone

                Use Color Picker.

                Given     Lab           80 10 -20

                Read     sRGB      203 193 236

                Read     CMYK     25 26 0 0     ISOCoated-v2-eci / Relative Colorimetric / Blackpoint Compensation

                Use Color Libraries, findet nearest Pantone Solid Coated automatically

                Read      531C

                Read      Lab          82 12 -15

                 

                For PS CS6 / new Pantone

                Use Color Picker.

                Given     Lab           80 10 -20

                Read     sRGB      203 193 236

                Read     CMYK     25 26 0 0     ISOCoated-v2-eci / Relative Colorimetric / Blackpoint Compensation

                Use Color Libraries, findet nearest Pantone Solid Coated automatically

                Read      2635C

                Read      Lab          77 11 -25

                 

                In my doc

                http://docs-hoffmann.de/swatch16032005.pdf

                on p.10:

                For       531C

                Read      Lab          82.03 12.21 -14.43

                 

                I can find the nearest spot color programatically (PostScript), see p.20 – p.32, but I don't have the

                new data base for Pantone colors (also, I think it's wasted time, following all these Pantone changes).

                 

                Best regards --Gernot Hoffmann

                • 6. Re: .ACO swatch file
                  zaki mohammed reda Community Member

                  Again, thank you so much Mr Hoffmann for your precious help !