Explanations about Image Resolution (DPI or PPI)

Thought of penning this down as a reference for anyone who is confused about image resolution (DPI or PPI), since I think there is a lot of misunderstanding regarding this topic, especially regarding the image resolution setting found in most image processing software when exporting.

To first lay down the basic terms for this discussion

• Image resolution refers to how many dots-per-inch (DPI) or pixels-per-inch (PPI) - effectively meaning how many dots or pixels are represented in 1-inch of display media.

• Image size refers to the dimensions of an image - for example the number of pixels of the length and height of an image.

The term PPI is a newer term, that became common from screen manufacturers’ usage to showcase how sharp (i.e. how fine the pixels were) a screen is. DPI on the other hand was a term used for a long time to discuss the image resolution of an image (either digital or printed) as well as for printer’s resolving power. However, most people or software do use these 2 terms interchangeably when talking about image resolution, so to simplify things we will just use DPI here.

Now a very common statement is: “The higher the DPI the sharper the image.”

There is no argument - this statement is true, but not for the saved “image resolution” setting within the image file, but rather the resultant DPI from printing the image.

What do I mean by that?

The DPI value itself is a ratio of the one dimension of the image size in pixels to its size in inches, and can be used for converting or calculating one or the other.

To put it mathematically,

• Image Size (pixels) / Image Size (inches) = DPI

Any two of these values are needed to calculate the third value, and specifying or locking two values would vary the third.

Here are some examples and comparisons:

1. I print an image with dimensions 3000 x 3000 pixels at 300 DPI, so the resultant print is 10 x 10 inches.
   The same image is printed at 100 DPI, and the resultant print is 30 x 30 inches.
   We know that a higher DPI is sharper, and you can imagine how a same origin image always look more pixelated when printed larger.
   In this case we have Image Size (pixels) and DPI, which controls the final print output.

2. I want to print 10 x 10 inches, and to maintain sharpness I set my image resolution to 300 DPI.
   This means that my images would be saved or exported to 3000 x 3000 pixels.
   A side note from this is that my original image size should be at least 3000 x 3000 pixels, so that it can be resized down to 3000 x 3000 pixels to maintain 300 DPI. Any smaller image (say 2000 x 2000 pixels) would be upscaled to 3000 x 3000 pixels, and thus losing some sharpness and clarity.

In these two examples, we have only the dimensions of the image size in one unit, and use DPI to convert the other unit for input or output.

Now what if we set BOTH the input size and output size?

• I have an image size at 3000 x 3000 pixels, and I know I am going to print it on a 10 x 10 inch paper.
  I have now the following options:

  • I can choose not to set the print resolution, and the resultant print would be in 300 DPI.

  • I can set print resolution at 300 DPI, and the resultant print would be the same as above.

  • I can set print resolution at 600 DPI, at which the software would upscale the image to 6000 x 6000 pixels to maintain 600 DPI for a 10 x 10 inch print, and then finally print the upscaled image at 10 x 10 inch. This image would look very similar, if not identical, to the above two options.

  • I can set the print resolution at 100 DPI, and the software would resize the image to 1000 x 1000 pixels before printing it out at 10 x 10 inches. This would lead to a softer print as compared to the previous examples.

With these explanations in place, now we can continue with the following deductions:

• By setting both the print size and the original image size, the resultant print DPI can just be determined by the ratio relationship. This resultant print DPI is what determines how “sharp” a printed image looks - the higher the better.

• If we set the print DPI to any number that does not correlate perfectly to the image size or print size, a resize (downscale or upscale) would happen and there might be loss of quality involved. While this may be useful when sending it out to a third party printing service, if printing directly from source image it is always better to leave the print DPI field empty if your resultant print DPI from the original size is above your requirements.

And with this comes the next question: “Does the image resolution field of an image mean anything?”

As mentioned, a digital image will always have its image size in pixels, and the stored DPI value is there to convert it to print size if the print size is not specified. Similarly, if you specify a print size, the stored DPI value is there to determine the image size to save as, so that when you print the image as it is it would be at the print size you previously specified.

However, just changing the “image resolution” field within an image file does not change the image at all - as mentioned it is a ratio used for conversion between image size and print size, so unless you specify a print size as well, regardless of what number you put in there the original image would not be affected at all.

You can test this out by opening an image, and changing just the “image resolution” field and saving it - the image size (and file size for that matter) should remain exactly the same.

Printing to a specific print size from an image, the “image resolution” field does not mean anything at all, and what matters is if you print it at its native resolution or you set a print DPI on the printer output.

So to summarize everything,

• The “image resolution” field within an image file is there to help convert from pixel size to print size when print size is not specified.

• Just changing the “image resolution” field within an image does not alter the image in any way, unless the print size is also specified (in this case original image would be resized accordingly).

• By specifying a print size from an image’s native pixel dimensions, the resultant resolution of the print can be used to determine how sharp a print is - this is in fact what the first statement, “The higher the DPI the sharper the image.”, refers to.

New Flexible Color Picture Control

I mentioned in my previous entry that I was quite intrigued about the new Flexible Color Picture Control when the Z6III was first announced, and during the touch-and-try event I managed to get some hands-on experience using the picture controls and spoke to some of the staff regarding its development and implementation.

As a brief introduction, picture control profiles are selectable profiles within the camera when shooting (both stills and video), which comes with a set of options that the user can fine tune to their liking for a certain look, and these settings are applied to live view previews (when Apply Settings to Live View/Show Effects of Settings are turned on), applied directly to saved JPG/HEIF files, and also used for the saved JPG previews within the RAW file.

In recent years Nikon has introduced more picture control profiles, such as creative picture controls that gives a more distinct look to the images via color casts and more manipulated tone curves, or multiple monochrome picture controls for different black and white looks - very similar to what other manufacturers do for film simulations or the likes.

And now what they are doing with the new Flexible Color Picture Control is to bring the level of color customization a step further to allow users to fine tune color casts, color blending, color grading on top of tone curve (contrast) and sharpness settings.

So before I continue, no, this is not a unique breakthrough or a game-changer of any sorts (yeah we all dislike this term don’t we), since other manufacturers usually have something similar in their cameras too.

But its implementation is something that I think is intriguing and am keenly interested to see how it will unfold.

As of writing, although the Z6III is the only camera that allows you to select Flexible Color in its picture control settings, I foresee it would come to other Expeed 7 bodies via a firmware update in the near future, like how the extra monochrome or rich tone portrait profiles were added via firmware updates to the Z8.

Even if the body does not support Flexible Color picture controls now, by using the official Nikon RAW development software, NX Studio (version 1.7.0 and above), you can now apply the new picture control to any Nikon RAW files (make sure you choose “Latest Picture Control” in the dropdown menu), and use it to color grade your photos within NX Studio.

Now comes the interesting part - your “recipes” can be then saved and exported, and with the upcoming Nikon Imaging Cloud service, users can share their flexible color picture profiles with others, and also download those created by other independent users or those done in collaboration with Nikon.

More information regarding how to use NX Studio to apply, export or import the new Flexible Color picture control can be viewed on Nikon’s official guide here.

Truth be told, I know NX studio is not the first choice of a RAW developer for a majority of photographers due to speed issues and lack of shortcut key customizations, and I am not in any way trying to convince any one here to move to NX Studio for full RAW development. But it can now be used as a powerful tool to create, tweak or import custom color grading profiles for your camera, and when the in-camera support comes for the other Expeed 7-based bodies, it would be useful in many workflows, especially those of dedicated JPG shooters. On top of that, using the flexible color profiles of other users also gives a chance to experiment with trying out different looks, and also learning how such looks are achieved by looking at how the color settings and tone curves are tweaked.

Capture One Pro Lens Profiles

When images are loaded or imported into Capture One Pro, lens profiles are automatically applied if they are available.

While the profiles made by the Capture One team are pretty accurate and work well, one shortcoming of using their profiles (or the Generic Pincushion/Generic Distortion profiles) is that any form of distortion correction will cause some pixel loss, so even if no resizing is done and the images are exported at full size, there is a chance that you will end up with images with slightly varying dimensions (depending on lens used and amount of distortion correction applied).

I have found that one way to circumvent this, if your camera body allows for it, is to use the “Manufacturer Profile” option, so even if distortion corrections are applied, the dimensions would remain the same.

Keysticks + Gamepad for Image Culling

A while ago I had this idea about using my gamepad for image culling.

And after experimenting with it with various software, I have to say I am really pleased that it works really well, and has sped up my work flow quite a bit!

The key-mapping software I am using is called Keysticks, a free open-source software, and am coupling it with my Xbox One wireless controller.

My current layout is like this:

• D-pad mimics the directional arrow keys

• Right joystick mimics the mouse cursor movement

• "A" button for 1-star rating

• "B" button for 0-star rating

• "X" button for 5-star rating

• "Y" button for "Hand" tool

• Right trigger for mouse double-click

• Right shoulder button for mouse single-click

• Left trigger for mouse scroll-up

• Left shoulder button for mouse scroll-down

And my workflow for culling is as such:

• After ingesting the files into Capture One Pro, first I press "Y" to make sure the hand tool is selected

• As I go through the images using the D-pad, I use the joystick to move my mouse cursor to roughly where I want to check for critical focus. A tap of the right trigger button will zoom in to 100% at the mouse location, and another tap would send it back to fit screen mode, making it easy to quickly zoom in and out to check critical focus.

• In the first round of image culling, I tag the images that have misfocused shots/blur shots/closed eyes with 1-star rating by tapping the "A" button. In the event I accidentally tag something wrongly, I cancel it using the "B" button (0-star rating).

• These 1-star rating images are moved to a separate folder, and I go through the remaining images in the original folder to select images I want to post process. This is done by using the "X" button to give them 5-star ratings, and cancelling accidental tags with the "B" button as well.

• If I need to check on some small details around the image (without the need for 100% zoom), I can do so with the left trigger button and left shoulder button (which mimics mouse scroll functions), and panning around can be done by pressing and holding the right shoulder button and moving the joystick.

• And finally by filtering to only display the 5-star rated images, I then proceed back to my keyboard and mouse for processing the images (yea I know I know..am just not a huge fan of pen tablets)

Using the gamepad to do the culling is an enjoyable relaxing experience so to speak, as I can literally lay back with a bad posture on my chair while going through the images.

I really want to give a shoutout to Keysticks for the wonderful software!

Now I wonder if a portable version that could run off a USB drive without any installation could be developed......

Lifelong Learning

It had been a crazy rollercoaster month with almost no breathing space for me, and finally I could manage some down time here to rejuvenate and catch up with every one around me.

So yesterday I met up with an ex-student of mine for coffee, and one of the topics that we were talking about was career choices.

I told her about my story - my initial plans for a career in science, how participating in the JET program widened my horizons, and the path that I am taking now.

In hindsight, I guess I had never told this in depth to any of my students before, so she was pretty surprised at my thought process, and also at the fact that I was influenced and changed during the time I had spent in the small city where I taught.

I also shared with her how much I was learning from the students from my time spent as an educator, and till this day I am still very grateful to the many people whom I had met and made connections with.

To be honest when I was first tasked to teach them English, I was quite worried if I would in fact be of any help to them. But under the guidance of the veteran teachers I slowly came to understand how to best help the students out in their English education.

And as I found out that I was learning so much from the students just by listening to their experiences, I realized that I could bring more to the table by sharing my own experiences and thoughts as well, so as much as I could, I tried to chat and have discussions that are not academically related with them as well.

If any of my ex-students is/are reading this, I hope I somehow manage to do a good job hahaha. (Or at least I hope I inspired something in you!)

I believe that education is a lifelong process, and we never stop learning and discovering new ideas. By sharing what you know, you would also discover what you do not know, and that would definitely help you mature and grow into a better person.