Jump to content

Recommended Posts

Posted

2.4, windows 11

Hi, when using the crosshairs and looking at the LAB values at the info panel the values are wrong (without converting to LAB). Also the range of the AOpponent- and the BOpponent-Channel does not go from -128 to 127 (it's much smaller).

Only when converting the image (via Document>Convert Format/ICC Profile) to LAB, the info panel shows correct LAB values and the range is correct.

Posted

Hi @stevenmiller,

The values you see in the Info Panel are displayed as percentages rather than 8-bit which I believe is a bug possibly related to AF-2424.

Affinity Designer 2.6.3 | Affinity Photo 2.6.3 | Affinity Publisher 2.6.3
MacBook Pro M3 Max, 36 GB Unified Memory, macOS Sonoma 14.6.1, Magic Mouse
HP ENVY x360, 8 GB RAM, AMD Ryzen 5 2500U, Windows 10 Home, Logitech Mouse

Posted

@Hangman thx for the info. But finally I figured it out, the values in the info panel are not shown in percentages. And there is no bug.

The reason is that LAB/16 has a bigger color gamut than RGB/8. Any image that has RGB/8 format cannot have the full range of LAB values. It is just as simple as that.

U can simply check as follows:
1. Draw a rectangle (vector shape).
2. Color panel: switch to sliders, choose LAB, set values (L,A,B)=(50,-128,0). That colors the rectangle green.
3. Convert back and forth between LAB/16 and RGB/8  (via Document> Convert Format) and observe the info panel.
4. Observe LAB values in the info panel: In LAB/16 format it shows (L,A,B)=(50,-128,0)   vs  in RGB/8 format it shows (L,A,B)=(56,-43,9).
5. Use online color space converter to check that this is indeed the result of the color space conversion.
    e.g. use https://www.easyrgb.com/en/convert.php#inputFORM

 

Posted

Hi @stevenmiller,

You're absolutely right... I'd been seeing what looked like some odd LAB values in the info panel even working with a LAB document and have equally been testing reaching the same conclusion...

 

Affinity Designer 2.6.3 | Affinity Photo 2.6.3 | Affinity Publisher 2.6.3
MacBook Pro M3 Max, 36 GB Unified Memory, macOS Sonoma 14.6.1, Magic Mouse
HP ENVY x360, 8 GB RAM, AMD Ryzen 5 2500U, Windows 10 Home, Logitech Mouse

Posted

Hi, @Hangman, true, you get values even working with a LAB document for the same reason. If the original image was created in (or converted to) RGB/8 the color gamut is restricted to RGB/8. Converting the document from RGB/8 to LAB/16 document cannot change that or restore any lost information.

1. Using the above example you can use LAB/16 format and create the (L,A,B)=(50,-128,0) colored rectangle with vector shape tool. Then export this as an image as .tiff file with LAB/16 color profile.
2. When opening the .tiff file, the info panel will show the correct (L,A,B)=(50,-128,0) values. But once you convert it to RGB/8 and then converting back to LAB/16 the info panel will always show (L,A,B)=(56,-43,9), simply because the conversion to RGB/8 will lose the color information past recovery.

What happens during the conversion is: (L,A,B)=(50,-128,0) gets mapped to (R,G,B)=(0,155,116) from the bigger LAB gamut to RGB gamut - this RGB representation of the original (L,A,B)=(50,-128,0) value triple is already an approximation (the original color info is lost). When converting back from RGB to LAB the triple (R,G,B)=(0,155,116) gets mapped to (L,A,B)=(56,-43,9) because the original info is lost for good.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

Terms of Use | Privacy Policy | Guidelines | We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.