What's new
By:
Photoshop Gurus Forum

Welcome to Photoshop Gurus forum. Register a free account today to become a member! It's completely free. Once signed in, you'll enjoy an ad-free experience and be able to participate on this site by adding your own topics and posts, as well as connect with other members through your own private inbox!

Actual Pixel Count in a channel


S

ScreenPrinterSA

Member
Messages
5
Likes
1
I am screen printer that uses Photoshop to separate our artwork for printing. We use channel for each colour that we print. Some designs might be as many as 13 channels. One of the major problems we have is that we can't accurately estimate the cost of the screen printing ink per channel.
If we were able to calculate the number of pixels per channel accurately (don't think Histogram is accurate) then in theory I should be able to work out to the cent how much ink is in a channel.

Is there any way of doing this ? or maybe there is a plugin or filter already available to do this?

Thanks in advance
 
Hi @ScreenPrinterSA

I may or may not understand your requirements yet let me tell you my assumptions and then an approach that can be used to give a close measurement of the ink used.
Assumptions
- Each unique color is identified in one particular channel in the Photoshop channels palette
- I will also assume, given that it is a screen print that each channel pixel is either solid white or solid black.
- I will also assume that black means there is a hole in the screen, meaning it prints the color for the black pixel location (if its inverse of that it is an easy conversion with the technique below)

If those assumptions are valid, here is what you do.

- You convert the black and white channels into their Layer of black and white pixels (that may already be the case yet I did not want to assume)
- on each of those Layers representing one color to screen, you use the Average Filter on each Layer. That turns the entire layer into one grayscale value
- With the info panel open, click on one of the eyedroppers, and change the reading mode to grayscale.
- With my assumption that a black pixel meant a hole where ink is passed through to the end product, the average gray value for each Layer then represents the percent of pixels where ink is being placed on the end product.
- Now if I have it backward and it is the white pixels that indicate where the ink is passed on to the product, then you just invert the percent number to have the percent of the document pixels for that Layer

I hope that makes sense. If my assumptions are correct and you need more details on the approach, just ask.
John Wheeler
 
Hi John,

Thanks for your reply , yes i think you have the gist of what i am looking to do. I have attached 2 photo's of a design separated into channel (screen printing colours) in Photoshop. This particular design is a 13 colour job as you can see from the list of channels. Yes the black area is the area that we screen print. From these channels we make positives (like an old fashioned negative in photography from years ago) and in tern we use the positives to make a screens.

What i need to find out , would it be possible to automate this process even if i have pay to have a filer or plugin written. My idea is two fold , namely to be able to cost accurately by knowing how much ink each channel uses to print 1 print and secondly at production stage where by I can determine how much ink is need for the complete order and thus to avoid ink wastage (big costly problem) as we always seem to mix way to much in production. I would be able to provide the number of pixels in a given solid area together with other required variables that would be required to perform the calculation if this info can be obtained.

What needs to be remember is that we do 15 designs like this a day , hence the need for it be automated.
I do believe if someone was able to successfully write something like this, there would be a huge market for it to be sold world wide as there is nothing like it available.


Frozen2.png
Frozen1.png
 
Hi @ScreenPrinterSA
I am quite sure that this can be done, most likely with a Photoshop script. A keyboard shortcut could call that script.
As with all software, though, the scriptwriter would need some explicit details on your needs and explicit details of what you are providing from within Photoshop.
Its often misunderstood user requirements or changing requirements add complexity to the software development.

I have done enough Photoshop scripting to know this is possible, yet not enough scripting to do such work productively.

There are some scriptwriters on this forum and Adobe Scripting forums elsewhere.

There is a forum on this site about Photoshop Automation that might be a good place to ask more questions including how to to find a scriptwriter.

Hope this helps

John Wheeler
 
I have taken a quick look.

The gray levels are proving to be an issue...

If each spot channel could be converted to a halftone, then the calculation used in the method that I am exploring would work as there are only white and black values. The screen frequency LPI would of course have some bearing. I am presuming that your ink use calculations are based on the current resolution of the document, not at a fixed value of say 1200 pixels per inch. You would have to make some adjustments to your calculation but this should be constant and workable.

Otherwise, all shades of gray could be calculated as black, however this would likely lead to inaccurate results over halftoning or dithering to simulate gray levels.
 
Last edited:
Thanks for looking at this

Would it help if i sent you a link to a we-transfer (55 meg file) with an actual separated document for you to view - maybe this will give you better insight into what i am trying to do.Obviously scope of work is critically important.
I am not an artist myself (I own the business) so i don't have a 100% working knowledge of Photoshop but i do have some knowledge.
I checked with the artist about working resolutions - when he is working with image on the screen he works at 700 PPI - when he plays each channel out to film (called a positive) , he plays them at 60 LPI. Each channel represents a colour which in tern is used to make a screen. So if there are 13 channel , this is a 13 colour design.

In the ideal world I would like to be able to click a button and Photoshop either spits out the monetary value of the pixels in the channel or if Photoshop can't do the maths , then a txt file with each channel name and the number of pixels in the channel. I have the other information available to do all the maths to do all the necessary calculations from these results. If Photoshop can't do the maths, I would write a program in C# to do the calculations.

I would do this project in stages , first stage would be to get the amount of pixels per channel sorted and saved as a txt document
Then i would look to do the calculation to get the costs of the ink
Then i would look to be able to input the quantity of prints required and do the maths to know how much ink is required for the job ( stop wastage - this is a major expense for me)
 
Yes, I can send you back the results from your sample file.

Ideally this would be a file that has already been accurately costed with all ink consumption costs and ink mixing volumes recorded.

Working backwards from, reverse engineering a known result is of course much easier than trying to create an accurate predictive model.

You might need to modify your formula as my proposed method would likely be based on different factors.
 
Back
Top