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The Myth Of 72dpi

I hear on a regular basis that images for web display must be set to 72dpi (96dpi Windows). The statement is simply incorrect.
Video monitors do not work with dpi. They display pixels. To put things straight – dpi/Dots Per Inch is a set of instructions for the printer, for the spacing of the dots/pixels when an image is printed.

So let's get print products out of the way first. Lets take an image of 500px X 375px. If you set it to 3dpi and print it, the print will have 3 X 3 dots spaced across each inch. The physical size of the print will be a whopping 168 X 125 inches, but you'll need to stand around 100 yards away to recognise it.

If we set the resolution of the exact same image to 300dpi the physical size of the image (kb) remains exactly the same, but when printed it will have 300 dots spread across an inch. The print size will be 1.67 X 1.25 inches – little better than a thumbnail.

3dpi/30dpiA comparison of 3dpi and 30 dpi in print
To Scale, but not actual size
Depending, of course, on your screen resolution (ppi)

Now let's take a look at video screens. Video screens only display pixels and are set to a screen resolution in ppi (Pixels Per Inch) a common setting today is, for instance 1920px X 1080px.
Any dpi information contained within an image is disregarded. An image with a pixel size of 500px X 375px will always display at 500px X 375px – on your monitor, on my monitor, or on Joe Blogs' monitor regardless of the dpi settings. It will never change either its pixel size, or its appearance. The physically displayed size will depend on your monitor's ppi settings.

Here's Proof That Video Systems don't use dpi
Don't believe me? Then take a closer look at the two images below. The first is set to 3dpi, the second is set to 300dpi. Both are 500px X 375px.
Do you see any difference? I don't. And yes, I have my glasses on.

Bike 3dpi
 Image set to 3dpi 

Bike at 300dpi
 Image set to 300dpi 

Still don't believe me? Then drag the images to your desktop (or right-click and save.)
Don't use the clipboard function. The copy function won't copy any dpi information and Windows image editors will automatically set the resolution to 96dpi, whilst Mac editors will set the resolution to 72dpi.
Now open both images in your favourite editor and check the size and resolution for yourself.

Believe me now?

It is important not to confuse PPI with DPI.
If you set an image to a physical size of 300ppi x 200ppi (px), but set your webpage to display the image at 500ppi x 300ppi (px), the browser will need to interpolate the image (i.e. replace the missing pixels with iterated (guessed) pixels, causing the image to look pixelated. If the same image is set to display at 200ppi x 150ppi (px) the browser will have to 'throw away' the excessive pixels – causing an an image to appear unsharp.

In the end, it's all just pixels.


Day Of Reckoning – RapidWeaver Calculator

Isn't it strange how two developers can release similar stacks within days of each other. Just a few days ago, it seems, I worked my way through the settings for a calculator stack. Now another one has suddenly appeared.

A quick look at the new CalcStack from Stacks4Stacks led me to believe that this was going to be a quick review. A more comprehensive examination proved me wrong.
Take it from me, the examples on the Stacks4Stacks page don't do the stack justice. Not only is CalcStack proficient with the four basic calculations, plus modulus, it integrates seamlessly with FormsPlus and can pass on its calculations to other contact forms – even the default RW form – and to other web pages for further processing.

Stack Settings
The very first option is Integrate With FormsPlus. Setting this option allows you to drop CalcStack into a FormsPlus field. It extends the FormsPlus code and becomes fully integrated. (Take a look at the demo project)
Next you'll find a choice of buttons that may be added to the CalcStack: Copy Answer, Mail-To, Reset/Reload, Submit Answer As Hash, Submit All Input As A Query (allows you to connect to an external page/site), Share To Twitter.
Extensive Style formatting options follow – too many to list here.

If you drag a CalcStack onto your Stacks page, you'll find it contains a child stack containing a one plus one calculation. You'll need to set a Calculation ID if you wish to use the results in further calculations – possibly something more recognisable than Calculation1.
Calculation Input settings start off with a choice of Input Types. The default setting is Number Box. Optionally, you can set Checkboxes, Fixed Value, Option Select Menu, Range Slider, Input or Answer From Another Calculation, or URL Query String.
Checkboxes will supply an array of checkboxes and associated labels. that provide a list of selectable items attached to a numerical value. Optional selection limits can be used to limit how many checkboxes a user can select. A selection limit of '1' gives the input a similar behaviour to radio buttons and permits only a single item to be selected from the list.
Option Select Menu provides an HTML select menu, allowing users to pick a single option. Not especially pretty (Will's own words), but extremely user-friendly and functional (especially on iOS and Android). This is a the input method to use if you need to be stringent about the values a user can choose from.
Both the Checkboxes and the Select Options are formatted with Markup.

Next – Input 1 Name, Default [value] and Steps. Steps allows you to define the incremented value displayed when the default Increase/Decrease buttons are clicked.
The Input Value can be hidden, but it will need a Operator – Add, Subtract, Divide, Multiply, or Modulus. Next follow the Input Values for the second numeral.

The Answer Settings give you the options Answer Decimals and Answer Name. The Answer may be hidden.
The Unit Settings will allow to to add both a prefix and a suffix to all three field labels – km/h, or ºC, for instance.

Once you have your first calculation, you can add a further child stack to take the calculated value and process it further. Will has provided a temperature conversion table as a simple example. E.G. Calculation1 – n minus 32 ºF; Calculation2 – Answer from Calculation1 multiplied by 5 (hidden); Calculation3 – Answer from Calculation2 plus 9 = n ºC


CalcStack is fully responsive, as you'd expect from a modern stack; will integrate with any theme and is a versatile calculation stack that will easily save you the costs involved with having a calculator specially programmed for your purposes.

If you need an online calculator and didn't already purchase the stack that I reviewed last week, I recommend that you check out the CalcStack demo pages (and 20 minute video) and download the demo version – Will is one of the few developers that offers demo versions of his stacks!


Online Calculations For RapidWeaver

If you sell a product or a service online, it's useful if your visitor can work out what he or she will need to pay before submitting an order. 1LD's new Formula stack can help your client with their calculations and simplify your order process.

Do you need to know how many tiles will be needed for that new bathroom wall? Or perhaps you want to spend the weekend at your favourite hotel in the Lake District and want to know what it will cost. With Formula you just need to add the wall's dimensions or the dates of your intended stay and the stack will do the heavy lifting for you by calculating the price and even packing the results into a contact form, ready for you to click 'Send'.

You will need to read the instruction manual before you can create your new web page. This is not criticism – once you've used it a couple of times, Formula is quite straightforward and intuitive – Formula will calculate almost anything, but you'll need to know how to proceed first!

When you drop Formula onto your new Stacks page, you will see a form with Input Field with an Import Value stack, Output and Formula. Plus a + button for child stacks. Click on the Import Value stack and check the settings panel. The Import Type can be set to Number Input (default), Checkbox, Select, Slider, or Date/Time Range. The Value is followed by an Import ID. So let's take a simple example and say you sell Coffee. And the smallest amount of coffee you can order is one pack. Set 'Amount' as the ID and the Min Value to 1. The Max Value can be set up to an indefinite amount, but let's restrict our customer to ordering 10 packs of coffee and set the Default order number to 1.
Leave the Styles at their default value for now – Single Column and Select Width 280px.

Now you can click the + button and add a new Import Value stack. Set the Type to Select, change the ID to Coffee and add Formula Selection options by clicking the child stack's + button. Arabica, Robusta, etc. Now activate the first Formula Select field and the price difference to your base product. E.G. Arabica costs €10 a pack, Robusta – our base product – costs €12; in the Formula Select field for Arabica, set -2. You get the idea?

Next you could add an Options Field with a Checkbox – For a Value Added Pack that is 20% more expensive than the selected product. In the Import Value settings, add an ID, a text description for the product, set the Disabled Value to 1 and the Enabled Value to 1.2. These are the multiplicators that will later be used to calculate the end price.

Now I could rewrite the complete Formula manual here, but I'll leave you to read it on 1LD's Tutorial Page.

Once you've added The import Values that your product requires, it's time to sit down and work out the formula for your calculation. If you write it down on a piece of paper, it will make things easier for you. Here's an example from our Coffee Sales Page: ((quantity * 12 + input-options) * value-added-pack) * (input-tip / 100 + 1). The formula includes a tip for the delivery driver.

Formula can calculate Addition, Subtraction, Division and Multiplication. The Formula is added to the stack with child stacks and in the settings panel, you need to set the Type of Segment – which also includes Import Value, Number, Parenthesis and Custom Expression.

I suggest that you set up Formula on a blank page – it gives you more room to work. Once you have your Input Values set up and your formula calculates the correct values, it's time to format your stack. The main settings panel gives you a choice of three Calculator Themes plus an additional Custom setup.The default theme is a light coloured theme, themes 2 and 3 are dark themes. Custom opens up a range of additional settings for the Background Colour, Borders, and shadow. Below the Custom settings, you'll find Padding values for the Input Fields, The Input Background colour, the Border Styles and Shadows. The Font Family expects a Google Font and has settings for the Size, Weight and Line Height. By default the theme font settings are inherited.

The Output settings Include Decimal Places, and Separators; Labels for the Answer. The Font settings duplicate the Input settings.
But I'm getting ahead of myself…
… the Output Answer also has a dropdown menu with the options Show Below Calculator Input, Show In An External Field, No Answer/Calculator Input Only and Show Answer Only/No Calculator Input.

The option Show In An External Field is of special interest. If you hover over the screenshot above, you'll see that in the second image, Formula is positioned next to a contact form (in this case 1LD's Super Forms). In the last field of the contact form, you'll notice the Total Price of the coffee that is being ordered. All other order details are being passed on to hidden fields within the contact form. Once Miss Jones has entered her contact details, she can click Submit and her coffee order will be sent off to be delivered in time for breakfast next day.

Full instructions for passing the Formula data on to a contact form are included on the Tutorial Page.

Formula is well thought out and will allow you to build the most complicated calculations that you can think of (unless you have a diploma in advanced mathematics). It's ideal for a booking form, small online store, or for calculating the cost of your new bathroom tiling – and it has the added value that the calculation can be passed on to you via email.

Now go forth and make those calculations work for you!


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