Script that copies the selected number of pixels

[heroleam]

Hi guys, I've been trying to make this script for a while and I can't get the result I need.

I'm trying to make a script that copies the amount of selected pixels to the clipboard, but it doesn't give the same value that appears in the histogram, can anyone help me?

#target photoshop

// Get the current Photoshop document
var doc = app.activeDocument;

// Get the brightness (Y) channel of the image
var channel = doc.activeChannels[0];

// Get the histogram of the luminosity channel
var histogram = channel.histogram;

// Get the total sum of histogram values
var totalPixelCount = 0;
for (var i = 0; i < histogram.length; i++) {
  totalPixelCount += histogram[i];
}

// Get the selected pixel amount value from the histogram
var pixelCount = totalPixelCount - histogram[0];

// Copy the value to the clipboard
var d = new ActionDescriptor();
d.putString(stringIDToTypeID("textData"), totalPixelCount);
executeAction(stringIDToTypeID("textToClipboard"), d, DialogModes.NO);

// Show an alert
alert("Pixels: " + totalPixelCount);

[Mike Bro]

Hello @heroleam,

I ran your script and it seems to be working as intended...

Regards,

Mike

[heroleam]

sorry, I forgot to mention that the channel needs to be grayscale.

[Mike Bro]

@heroleam 

I ran your script again on a grayscale image and it seems to be working as intended...

Regards,

Mike

[heroleam]

that's strange, try this file of mine here then

[jazz-y]

You see the cached histogram. Caching levels (which you can set in the performance settings) allow you to speed up the application due to the fact that Photoshop divides the bitmap into small tiles (something like a reduced copy of the image in memory), in particular, this approach allows you to speed up the display of histograms.

 

[Mike Bro]

@heroleam,

As @jazz-y pointed out, you need to hit the refresh in the histogram panel to get the correct calculation "pixel count". I found I only needed to do that if the area selected included any of the white background.

Regards,

Mike

[heroleam]

I understand, but I needed to get the value that is there without updating the cache.

I'll explain why, I work with serigraphy, we need to split the channel in the channels because we separate each color into a channel for recording the frame to print, after splitchannel we convert the channel to bitmap at 600 dpi per cm and then convert it to grayscale, we do the selection of the channel and we invert it to stay only where there is color, and the result of the pixel is used in a formula here of ours to measure the amount that needs to be used to print, all because of costs, so I can't update the cache because if you are not going to break the cost of the material to be used, that is why I need you to copy exactly the value that appears there in the histogram

[jugenjury · Accepted solution]

For cache level 2, divide totalPixelCount by 4.

For cache level 3, divide totalPixelCount by 16.

For cache level 4, divide totalPixelCount by 64.

This won't match what's shown exactly because they use some fuzzy logic algorithm around the edges, but it will be close.

I'm trying to figure out a way to determine with javascript which cache level the histogram is using on the current pixel count but it has been a bit elusive.

Not sure if that helps, but so far that's the best I can do. I know you wanted it copied to the clipboard but with a simple script like this, it would have to copy all of them or a predetermined cache level which you would have to input. Another option would be to have the script pop up a window with 4 selections and you select the current cache level from there and it will copy that value into the clipboard.

[jugenjury]

OK. I figured out the "fuzzy logic algorithm" part and it isn't so fuzzy afterall. To get the histogram pixel counts for each cache level...

// Save the current preferences
var startRulerUnits = app.preferences.rulerUnits
var startTypeUnits = app.preferences.typeUnits
var startDisplayDialogs = app.displayDialogs
// Set Adobe Photoshop to use pixels and display no dialogs
app.preferences.rulerUnits = Units.PIXELS
app.preferences.typeUnits = TypeUnits.PIXELS
app.displayDialogs = DialogModes.NO

// Get selection bounds
var sel=app.activeDocument.selection.bounds;

// Get selection width and height
var w = Number(sel[2]) - Number(sel[0]);
var h = Number(sel[3]) - Number(sel[1]);

// Get Pixel count for each histogram cache level
var l1 = w * h;
var l2 = Math.ceil(w/2) * Math.ceil(h/2);
var l3 = Math.ceil(w/4) * Math.ceil(h/4);
var l4 = Math.ceil(w/8) * Math.ceil(h/8);

//Restore prior preferences.
app.preferences.rulerUnits = startRulerUnits
app.preferences.typeUnits = startTypeUnits
app.displayDialogs = startDisplayDialogs

I still haven't figured out how to get the current histogram cache level.

[heroleam]

how would it look in the complete code?
Just to point out, I didn't make this script with my own knowledge, I made it with the help of chatgpt, so could you show me how the code would look completely?

[jugenjury]

I can. Let me try to work out a bit more on this. I think I've come close to figuring out how to determine the cache level. I'll have some time later.

[jugenjury · Accepted solution]

Also, as an FYI, the histogram cache level is based on the sample size (the size of your selection). Once you get around 400,000 pixels selected (slightly less than that) it shifts to the next higher cache. Level 2 combines 4 pixels into one so the number of pixels you see in the histogram is 1/4 the total number selected. Level 3 combines 4 of level 2 pixels together into one so the histogram shows 1/16 of the total number selected and Level 4 combines 4 of level 3 pixels so it shows 1/64 of the total number selected. Is this what you want to get? Mathmatically this make sense to me if your end goal is to resize smaller to stay within a certain print size based on your pixels per cm. If that's what you're trying to do, there may be an easier and more accurate way to do this.

[heroleam]

I just need it to save the value of the pixel that appears there in the histogram, and not what is behind the code, according to my print at the beginning

[jazz-y]

I'm sorry, but this sounds absurd. If your image has ACTUALLY 95534348 pixels, then why do you need to know how many of them Photoshop uses in its calculations? If you change Photoshop's performance settings, the numbers will be completely different. How can you base your calculations on these values if they have nothing to do with the physical process of printing?

By the way, I noticed one mistake that probably affects your results - above you write that you change the file resolution to 600 dpi. At the same time, the file you attached has a resolution of 600 pixels/cm (!!!). This is 1524 pixels/inch. If we change the file resolution to 600 pixels/inch, we get a value of 14808800 pixels in the image, which is (apparently) much closer to the result you expect. Please check it.

 

[heroleam]

it's because you're seeing it in inches, if you change it to centimeters it will give you 600 dpi.

[jazz-y]

DPI = Dots Per Inch (in digital files, dimensions are indicated not as DPI, but as PPI, but, at the user level, we do not distinguish between these terms)

600 pixels/cm not equal 600 pixels per inch

600 pixels/cm equal 1524 pixels per inch

You increase the number of pixels in the file by 2.54 times and then wonder what you get from a script that counts them as incorrect (in your opinion) 🤷‍

[heroleam]

it's just that here in Brazil we call it dpi in general, we don't make this division, the people here understand each other.
And that's what I said there before, 1054 dpi/in would be 600 dpi/cm

[heroleam]

1524 dpi/in***

[jugenjury]

Try this. The only thing you might have to change is the first line. You have to set the var cacheLevels to whatever is set in your preferences. I put it at 4 since that seems to be the Photoshop default value.

#target photoshop
// Set cacheLevels to the number as set in preferences (performance tab)
var cacheLevels = 4;

// Get selection bounds
var sel=app.activeDocument.selection.bounds;

// Get selection width and height
var w = Number(sel[2]) - Number(sel[0]);
var h = Number(sel[3]) - Number(sel[1]);

// Create dialog window
var win = new Window('dialog', 'Histogram Pixels');
win.size = [200,200];
win.button = new Array();
win.pixels = new Array();
var u = undefined;
var cLevel = 0;
var totalPixelCount;
pix = new Array();
var p = 20;
for (i=1; i<=cacheLevels; i++) {
pl = Math.pow(Math.pow(4, i), .5)/2;
pix[i] = Math.ceil(w/pl) * Math.ceil(h/pl);
win.button[i] = win.add('button',[20, p, 60, p+20],'Level '+i);
win.pixels[i] = win.add('statictext',[80, p, 150, p+20],pix[i]);
win.button[i].value=i;
win.button[i].onClick = function() { cLevel = this.value; win.close(); }
p+=35;
}
win.cancel=win.add('button',[50, p, 70, p+20],"Cancel");
win.cancel.onClick=function() { win.close(); };
win.center();
win.show();
if (cLevel > 0) totalPixelCount = pix[cLevel];
else totalPixelCount = "Not Selected";
// Copy the value to the clipboard
var d = new ActionDescriptor();
d.putString(stringIDToTypeID("textData"), totalPixelCount);
executeAction(stringIDToTypeID("textToClipboard"), d, DialogModes.NO);

alert(totalPixelCount);

[jugenjury · Accepted solution]

I'm also confused just like jazz-y is. Mathmatically this makes no sense. If you're trying to figure out how much ink or whatever for your print job based on the pixel count and the pixels per cm (or per in, whichever it is) you would probably want to know the actual number of pixels in the selection and not the combined pixels as shown in the Histogram window based on cache level. As I mentioned above, the cache level is based on the size of your selection and anything other than level 1 is not your actual pixels.

Example. Let's say you select an area that is 400 x 999. It will most likely use cache level 1 and give you 399,600 pixels. If you moved over 1 more pixel in your selection to 400 x 1000, you would drop to cache leve 2 and get a pixel count of 100,000 even though you actually added 400 pixels to your selection.

[heroleam]

it's still giving a value out, my cache is at 4

[heroleam]

Guys, I talked to the people here and we are going to evaluate the information that you passed on.

So how could we do it right? follow the process we do:
We split the channels
convert to bitmap 600dpi per cm

frequency 25

after that we convert to grayscale

we select the channel and invert it so that the selection is only where there is color.

this would be the process to store the value of the pixels generated there

after that, the pixel value is placed in a spreadsheet to calculate consumption

Follow the link to the spreadsheet to consult: 

https://docs.google.com/spreadsheets/d/14OKhSHX4NjkrBvdsCnKzQfdV_lbwngszKdtGOyzbBBo

Now knowing that, what would be the most correct way to make the calculation work?

[jugenjury]

Are you only doing this on one channel or all channels one at a time?

And FYI, the abbreviation "dpi" stands for dots per inch. Dots per cm would be "dpc". 

Are you using RGB channels? CMYK channels? Lab channels? The example you posted only has the one channel. I see 3 mixes on your spreadsheet so I'm guessing each mix is for a particular channel (color). Please correct me if I'm wrong.

Is the end goal here to determine how many pixels of each color are present in the image? Are you looking for just a straight pixel count of an overall value that determines how much of that color is present. For example, a single pixel if using RGB would have some Red, some Green, and some Blue but not always 100% of each (unless it's white). Of course for printing that would be opposite but same principle applies. What I'm getting at is are you looking for a totalizer for the pixels values or assuming all pixels are 100% and just counting them? Either way, I could see about coming up with a better method now that I'm more understanding of what you're doing.

Do you have an example file you can share? One that has the color and let me know which colors you use for your inks/pastes so I know how to break it down? If you're allowed to, that is.

[heroleam]

The mix there in the spreadsheet does not mean mixture, it's just that for you "mix" is to mix, but here "mix" is the name of the product.

The objective is to know how much product we will use per area of the drawing.

I will send you the file here with the colors, each channel will be a frame to print.

You need to use splitchannel on the channels and use the action on each channel to then do the pixel count.

Action: https://we.tl/t-oiFanfHUx7