Jump to content

Select pixels with defined RGB values

Recommended Posts


is there any possibility to select pixels with specific RGB values in Affinity Photo?

For example, in an picture from a fluorescence microscope, I would like to select all pixels with RED values >251.

I already tried with mask followed by a brush with different red values, but this did not work.

Unfortunateloy, with "Select/Color Range/Red" I cannot define the minimum red level of the selection. Seems to be a fixed value.

Any idea?



Share this post

Link to post
Share on other sites
On 5/16/2019 at 8:23 PM, >|< said:

Here's a macro: Select pixels above some red threshold.afmacro

Select a Pixel object then run the macro. If another type of object is selected then it will be rasterised at the beginning of the macro. The red threshold defaults to 98.431%, which was set by entering "251/2.55" (without quotes) in the percentage field of a Threshold Adjustment when recording the macro.



Thanks for sharing your idea. Unfortunately, this is not accurate enough. With a threshold of 94%, only pixels with a red value of 255 are selected. With 93%, pixels with red values >237 are selected.

Share this post

Link to post
Share on other sites
On 5/16/2019 at 5:17 PM, carl123 said:

Can you upload a sample image. 

My fluorescence microscope is stored in the garden shed at the moment and it's raining.


Thanks carl123 for this valuable posting. I assume your other 2296 postings are of similar meaningfullness.

Share this post

Link to post
Share on other sites

Just tried again. It works, but only with your pre-defined 98%. When I enter any other number directly into the field which pops up after starting the macro, nothing changes. It only works when I pull the slider with the mouse. But this is not accurate enough (I think the macro takes into account your calculated 98,431%, although only 98% is shown).

However, your macro seems to be the perfect solution for me, if only I could change the 98% to different numbers, and I need it also for other colors.

Could you explain the single steps to create this macro? Obviously, you did not do it via "Select/Select Sampled Color...".


Share this post

Link to post
Share on other sites

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.

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.

  • Create New...

Important Information

Please note the Annual Company Closure section in the Terms of Use. These are the Terms of Use you will be asked to agree to if you join the forum. | 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.