AP version 1 - Load spare channel and fill problem

[henryanthony]

I built a Spare Channel with 11 stripes, equal in width that change in value from 100% to 20% in steps of 8% as shown in the first row of numbers below.

100 - 92 - 84 - 76 - 68 - 60 - 52 - 44 - 36 - 28 - 20

100 - 95 - 88 - 80 - 72 - 62 - 53 - 42 - 32 - 22 - 13

I load the channel to a Pixel Layer, fill with 100% black and the result is stripes with values shown in the second row of numbers.

My expectation is that the values in the Spare Channel should match the values in the Pixel Layer. I get similar results in RGB and CMYK. I have been able to tweak the Spare Channel to get the values I want but, I am wondering what might be causing the difference of input versus output values. Or could it be I am not understanding my process?

Thanks!

[NotMyFault]

Hi,

1. can you please share the Affinity file? It will help us to reproduce.
2. how do you read out the color values? Depending on color format and color profile, you may get misleading (wrong) results. In principle only sRGB gives somehow accurate results, but limited to 8 bit.
3. using the color picker from color panel averages over multiple pixels, so you need to pick from a solid colored area large enough to avoid averaging with adjacent areas.

 

[NotMyFault]

On 10/24/2023 at 1:03 PM, henryanthony said:

I load the channel to a Pixel Layer, fill with 100% black and the result is stripes with values shown in the second row of numbers

I don’t understand this sequence of steps. If you fill with black, it would overwrite the loaded channel from the step before. Or do you load/fill only specific channels? If possible, please explain in more detail, or provide a screencast.

[NotMyFault]

On 10/24/2023 at 1:03 PM, henryanthony said:

My expectation is that the values in the Spare Channel should match the values in the Pixel Layer.

This is my experience, but only as long as you stay in same color format and color profile.

[NotMyFault]

On 10/24/2023 at 1:03 PM, henryanthony said:

I built a Spare Channel with 11 stripes, equal in width that change in value from 100% to 20% in steps of 8% as shown in the first row of numbers below.

How did you create this?

1. rectangular shapes with color by color panel. Please ensure the matching color model is chosen
2. by procedural texture filter? This would be the most exact option
3. by using a black-to white gradient and posterize filter?
4. by Selecting areas and using fill tool?

every methods has it up-and downsides what can go wrong.

[henryanthony]

Hi @NotMyFault , To clarify, I changed the percentage values from the original post. File is attached as well as a video of the steps used to create it. Note, there is a bit of dead space at the beginning of the video so give it a minute to begin.

I built a Spare Channel with 11 stripes, equal in width that change in value from 100% to 5% in steps of 10% with the last stripe being 5% as shown in the first row of numbers below. The second row show the values resulting from loading the spare channel to pixel selection and filling with 100% K.

100 - 90 - 80 - 70 - 60 - 50 - 40 - 30 - 20 - 10 - 5

100 - 93 - 84 - 74 - 62 - 50 - 37 - 24 - 13 - 6 - 4

Color Picker values were selected from a solid filled area 491 px wide so should not be a problem with any averaging.

I have included the file (AP Version 1 last update) and a video of steps taken to build. Video is not a strong point for me so sorry if it is crap 😉. Selection from dropdown menus do not record but this is a simple workflow but please let me know if you have any questions about it. The basic steps are listed below:

1. Open file and under Channels, select Create Spare Channel.
2. Click on Spare Channel and the images changes to 100 Gray and, the Gray slider, is the only one shown.
3. Using the Rectangular Marquee Tool, select a rectangle on the right and from top to bottom according to the Guides .
4. Fill the rectangle with Primary Color which is Gray 100. Repeat with each column and reduce Primary Color by 10 each time but fill the last column with Gray 5.
5. Click Add Pixel Layer. Change the Color Sliders to C-0, M-0, Y-0, K-100
6. Right click Spare Channel and select Load to Pixel Selection.
7. Click Edit > Fill with Primary Color and the Pixel layer should show 11 vertical bars with the various levels of Gray that now match the second row of numbers shown at the top of this reply.

5401 11 Template.afphoto

[NotMyFault]

Hi,

the process seems a bit overly complicated to me. The file is CMYK with a pixel layer with columns in  the alpha channel only. This  complicates everything. By layer blending (with implicit white background) you get color values in all channels, but this will give muddy colors in CMYK, probably not what you intend to get.

can you please elaborate what values do you want in the cmyk and alpha channels (for every channel)?
e.g.

• alpha should be 100% 
• K should be values according to you table
• cmy should be 0

Or something different?

[NotMyFault]

I would suggest a different workflow:

1. create new document
2. add pixel layer
3. fill with white
4. select rectangles
5. fill with color of same color format.
   1. Use grey only for grey/8 or grey/16 documents.
   2. use only one color channel for RGB and CMYK, e.g. R or K
6. when finished, save as spare channel.

i don’t see any benefit editing a spare channel directly. It is a rarely used feature, and color format conversion issues can bite you everywhere. Editing as pixel layer gives you the full spectrum of edit functions, adjustments, and filters. I use channels panel only to load / store channels between layers, and of course manage which channels get displayed and edited, but never to edit a spare channel directly.

[henryanthony]

For me - a confusing person - this workflow is simple and straight forward. All I need to do is use an alpha channel to load various selections to a Pixel Layer that may be rectangular or any other shapes and patterns with a variety of fill percentages of any color. Then I can use other tools in AP to further edit the layers as wanted. The final result will be used in textures in Blender. Please see the attached video to see how I use the Alpha Channel.

I hate to say it but, I am able to do this in Photo Shop easily with no selection percentage change from Alpha to Layer. The version of PS I have on my machine is PS 5 - LOL! I would be using that except for the fact that compositing some layers together causes unwanted artifacts. I have PS CS2 on a XP machine that works well but I can't load that to my Win 10 laptop and I won't trust my work to an over 20 year old computer. Plus I find AP to be so much better to work with and has some features that I find very helpful.

So, I guess I will never know why AP changes values from those input to an Alpha Channel compared to what is filled in a layer after Loading Alpha to Selection. No matter, I can and will work around this. Not that big of a deal.

Cheers!

[NotMyFault]

Sorry to disappoint, i never used PS after V1.0, and using channels it is better not to try to mimic old PS workflow in Affinity. The UI concept differs to much. I did not yet fully get what you are trying to achieve, it seems you want to create an alpha mask with 11 columns of alpha values. This is easy to achieve in Affinity, but again i`m unable to understand your PS inspired workflow.

[lepr]

3 hours ago, henryanthony said:

So, I guess I will never know why AP changes values from those input to an Alpha Channel compared to what is filled in a layer after Loading Alpha to Selection.

For your particular workflow, if your document is CMYK, you need to specify K-only CMYK values (that is, C:0, M:0, Y:0) to fill your spare channel to get the spare channel to contain the values you expect. Specifying values in any other way will result in the spare channel containing values that you are not expecting.

By the way, I advise you do not use Affinity's Info panel for inspecting CMYK values in a document. Use the colour sampler in Colour panel, as you did in the first video, to discover true values.

Edited October 29, 2023 by lepr

[lacerto]

Obsolete.

[henryanthony]

@NotMyFault, @lepr and @lacerto

Firstly, thanks and, because of your comments and answers, I have found that I have misunderstood how alpha channels actually work. I have tested what I built in AP with Alpha Channels in Photoshop 5.0, which I thought I understood, and have found that the results are the same that I get with AP. So, with this new knowledge I think I can move forward with my bucket list project. 

Cheers!

 

 

[henryanthony]

@lacerto Thanks for the tutorial vids. I am now working to duplicate what you did. I sure appreciate you taking the time to do these!