Understanding & Managing Image Quality – Part II
Understanding & Managing Image Quality – Part II
By Marc F Alter
In the last session we discussed some of the critical elements in creating quality images in digital photography. Amongst these were Bit Depth, Color Space and File Types. Increased Bit Depth allowed us to create images with a larger number of colors (16.7 million for 8-Bit versus 281 trillion for 16-Bit), Color Space (sRGB vs Adobe RGB vs ProPhoto RGB) defined the colors that are available, and File Types (mainly JPG or RAW) each had their own advantages and disadvantages but basically JPGs rely on the camera to preprocess our images while RAW demands we do it ourselves.
We also discussed that when we take a picture using a digital camera, the camera’s sensor captures the scene and records it in the form of Pixels. These Pixels are essentially data representing tiny dabs of color (Hue, Saturation and Light). If we look at our image normally (Zoom Out) the formation of Pixels causes our minds to recognize shapes, patterns and light. If we look at our image close-up (Zoom In), we can actually “see” the individual Pixels.
Using these concepts, we can now discuss the things you can do to improve the quality of your images.
Whether film or digital, knowing the basics of Photography is important if your goal is to take your camera off “Automatic” and create better and unique images. Some of these include knowing the Exposure Triangle (and the trade-offs between ISO, F-Stops and Shutter Speed), becoming familiar with Compositional Rules (really more like Guidelines), and learning about Light and its characteristics (Intensity, Quality, Color, & Direction), These are all important concepts to learn and become knowledgeable about (before going out and shooting).
Knowing and becoming intimately familiar with your camera, its functions, capabilities and limitations are also critical elements to creating a successful quality image. When a scene unfolds before you, you need to be ready to “Capture” it, for in a second it will be gone forever (photography is about capturing split seconds of time). Chief amongst these functions are knowing how your camera needs to be set and used to get good exposures and focus. Setting ISO (Film Speed / Sensor Light Sensitivity), F-Stop (More Light / Less Light and DOF-Depth of Field) and Shutter Speed (Short or Long Slices of Time). Also needed is knowledge on how to set different Exposure Modes, Metering Modes and Exposure Compensation. Focus is equally important. Knowing the different Focus Methods, Focus Modes and Focus Areas will help your image tell the intended story. Finally knowing more advanced camera functions, like how to manage White Balance, take single or bursts of shots, displaying a Grid for compositions, using custom programmable buttons, switching from Photo to Video, being able to view Exposure Highlights and Histograms, using “Live View”, etc. might not always seem important until the time when you need to use it.
Once you have learned these concepts and are familiar with your equipment you are ready to go out and shoot. As in most tasks in life, planning is an essential element of success and the same is true in Digital Photography. Whether you have a pre-conceived concept of what you what to achieve or just going out to “wing it” and capture the scene as it unfolds before you, knowledge of where you are going and then preparing for this will greatly enhance your chances of success. Knowing the weather, wearing the right clothes, having food & water available could increase the time you are out shooting and also make it more enjoyable. Gathering your equipment ahead of time, making sure it is clean and working will help prevent possible problems when “in the field”. Finally, check your camera’s settings and make sure they have been reset since your last excursion (nothing is worse then getting to a spot where a unique scene suddenly unfolds, you take the shot and then see your exposure or focus is set for a completely different event).
Capture represents the act of actually taking the picture and recording the image on the camera’s Memory Card. As we discussed, prior to capture there are several tasks you should take prior to going out. That being said, it is always good to review these settings (again) when out in the field.
After taking your shot it is best to review your Image on the camera’s LCD (Display). Most of today’s digital cameras can display a host of useful information including the Image itself (so you can check the composition and focus), Blinkees and/or Histogram (to see if any areas have clipped highlights or dark areas) as well as the ISO, F-Stop and Shutter Settings. After reviewing, you may wish to make some setting changes and shoot a similar image again. Unlike film which is limited to only taking a certain number of shots, most Memory Cards have greater storage capabilities as well as the ability to create more room by deleting pictures you know are not good.
Should you delete pictures when out in the field? That all depends on the image in question, your intension and/or if you have similar images. Care must be taken when reviewing your image on the camera’s LCD, for although it is useful, it can also be misleading. The LCD itself is small and even if you zoom in (ie; to check Focus Sharpness), the display can be misleading. Also, most LCD display only JPG images and these are pre-processed and can be somewhat misleading. The camera’s displayed Blinkees and Histogram may be reading the Image’s JPG values and not the actual values picked up by the sensor. This is especially important if you are shooting in a RAW format as the JPG data may not accurately reflect what the camera’s sensor is actually recording (it does however, give you a good approximation).
Everyone processes images differently. This is why today’s photography is an art form as much as it is a science. From the photo editing tools we use (and there are many to choose from) to the workflow we develop, there can be vast differences in not only how we captured the image before us but also in how we process it. That being said, to create high quality images, there are a few “Best Practices” that should be followed:
No matter what technique you use (any of the above, others or combinations), eventually you will find them inadequate. This does not mean you should not use them but rather you should along with your software’s capabilities. Many “Photo Browsing & Editing” software has the capabilities of using the Image’s Metadata to help you locate specific images (ie; Images taken at a specific time and place). Other software capabilities also allow you to further Categorize your images using Keywords, Colors, Star Ratings, Labels and/or Combinations of these. These can be extremely useful when trying to locate a specific image, especially as your Image Library grows.
Best Practices means shortly after we have transferred our images from our camera to our computer’s storage, we should review these and delete the ones we know we will never need. Chief amongst these would be those out of focus and those with poor exposures but where better exposure images exist. Beware because as digital technology changes as well as our own expertise, our ability to improve images, even those of questionable quality increases over time. Also, as we become more experienced photographers (and artists) we may delve into other areas of Photography (like Impressionism) where poorly exposed, out of focus and blurred images may be exactly what we are looking for.
Most good backup plans contain (2) main elements; Redundancy & Consistency. Redundancy means you have several copies of your programs and/or data in different places. This is because the media on which you backup your data can also fail (usually at the worst possible time; like when you most need it). Consistency means you perform your backups on a regular basis (either manually or automatically).
Backups should take into account, several different disaster scenarios including simple hardware failure, loss of power, water damage, etc to name just a few. Some of the most overlooked and misunderstood but common computer disaster scenarios involve being infected by a Computer Virus (like a Crypto-Locker virus which locks up all files you have access to), Technology Changes (where older media is no longer accessible) and Policy Changes (Cloud and other backup services that change their data retention services). Not only must special precautions be taken to avoid these, but most backup plans do not properly take these into account. When thinking about developing a backup plan and how you are going to implement it, keep thinking about what kind of failures or disasters can happen and how your plan will overcome these.
Monitor Calibration typically involves a sensor that is placed on the front of your screen as well as software that uses this device to analyze the sensor and create a file that sets (controls) your monitor’s brightness and displayed colors. There are several different types of Monitor Calibrations available, but most work the same way. Some monitors perform self-calibrating while others have Monitor Calibration built into them, but it is questionable how well most of these work as they usually require “visual perceptions” rather than measured sensored values.
Updating Meta Data is also an important task to consider. Nowadays, most digital cameras include common Meta Data embedded in each image file and includes useful information such as Date Image Was Taken, Camera Make & Model, Lens Make & Model and Exposure Settings. You should highly consider adding Copyright and Contact Information, so your ownership is clear.
Learning and using functions for managing Color Profiles, Bit Depths and Cropping (Delete Pixels or Not?) are important when editing a digital image. So can advanced capabilities such as Smart Objects or use of 3-D Imaging. One of the first tasks you should take when evaluating an image is to evaluate your image in terms of Colors, Hues and Luminosity to make sure the colors you are using are “in Gamut” for the devices/devices that will be used to view or print your image. Using Lightroom, Photoshop and/or many other Photo Editing programs, this is typically found as “Clipping Warnings” (both for Highlights as well as Darks). If your software does not have this function you should be able to view the image’s Histogram.
With digital editing tools becoming more and more advanced and with additional third party applications offering exciting new capabilities and ease of use, the possibilities are virtually endless. A good Rule of Thumb is to make as little changes as possible while at the same time managing White Balance, Exposure, Subject and Focus. One of the last functions to master is proper Sizing for Output, Sharpening and Color Profile Conversion.
There are two basic types of output, Printing and Digital Display. Each has its own characteristics, limitations but also some similarities. When developing an image for output and considering Image Quality, you must consider the media from which your image will be viewed.
Note: Do not confuse DPI, PPI and MP. Many people believe these are the same but, they are very different. DPI refers to Dots Per Inch and describes Dot Density (how many dots of ink a printer can print on a page). As such, DPI has no bearing to a Digitally Displayed Image. PPI refers to Pixels Per Inch and describes the Resolution of a device displaying a Digital Image. MP (MegaPixels or Millions of Pixels) refers to Image Resolution and represents the number of Pixels in the image. Careful to note that MP (ie; Image Size) alone does not determine Image Quality as Bit Depth (which controls the number of Colors, Hues and Luminosity) is also a determining factor.
Digital Display: When exporting an Image for Digital Display, consider where and how your image will be viewed. If you image will be viewed on the Internet, it means that many different platforms and devices (Monitors, Cell Phone Screens, etc) will be used to display your image. Many of these devices have very limited Color Profile capabilities (they can only display a limited number of colors) as well as low PPIs. As such, to prevent these devices from automatically recalibrating the colors in your image, it is best you do this yourself. In many cases using a Color Profile of sRGB and a PPI as low as 72 is good for most Internet viewing platforms.
Various Social Media environments have different recommended sizes for optimal viewing. As society’s devices and technologies change, so can the recommended Image Resolutions. Some of the most common Social Media Recommended Sizes (in Pixels) for 2019 are:
Other than Social Media, If you know your image will be displayed on a high Resolution platform (ie; the Huntington Library’s 4K HDTV used in HCC Image Competitions), you will want to find out and conform to the optimum Resolution and Color Profile of the device being used (in the case of the Library’s 4K HDTV, this means creating an Image Size of 3240 Pixels x 2160 Pixels with a Color Profile = Adobe RGB). Displays with higher resolutions will display Pixels as smaller but with greater density, thus they will look sharper and display better Color then lower resolution devices.
Printing Your Image:
As with Digital Displays, when printing an Image, Color Profiles matter. If your printer is not capable of producing the colors in your image, it will automatically disregard those colors and replace them with what “it” thinks are the next closest colors. This could result in banding and/or color shifts. Make sure the Printer you are using can handle the Color Profile set in your image. You can check your Printer’s Manual or Specification Sheet for this information or if necessary, contact the Printer’s Manufacturer. If necessary, learn how to Manage and/or change the Image’s Color Profile during output.
Image Resolution / Image Size also matters. Image Resolution is the number of Pixels along the width and length of your image. The more Pixels Per Inch, the sharper your image can appear when being viewed. Also, the more Pixels in your image, the larger will be that Image’s File Size. An image that has 3744 Pixels x 5616 Pixels is considered to be 21 MegaPixels (3744 x 5616 = 21,026,304 Pixels or 21 Million Pixels = rounded to 21 MP).
Note: The number of Megapixels should not be confused with the number of colors in your image as many of the Pixels may contain the same color.
In most cases, if your Image has too many Pixels, it will be ok. In some cases however, the printer may need to determine how to handle these extra Pixels. If your image is too small and does not have enough Pixel information, your printer will also automatically try to compensate. This is similar in concept to a rubber band. Without increasing the number of Pixels but increasing the output size, you are telling the Printer to do the best it can by reorganizing the existing Pixels. These Printer calculations could result in Pixilation, the creation of Artificial Artifacts and/or Unsharp Images. To ensure your image is sized properly, do some simple math:
During Photo Editing you can resize your image for the Optimal Output. When doing so your Editing Software will use various algorithms to try and obtain the desired size and resolution. If resizing an image to be larger, be careful to do so in small increments (no more than 10% each time). This would allow the Photo Editing software to more accurately create additional PPIs by sampling the surrounding Pixels. Resizing in larger amounts will cause your image to lose sharpness and could introduce color shifts. There are some Photo Editing software products currently available that will do much of this resizing for you, but it may be best for you to first learn the techniques yourself.
Managing Color – You or Your Printer?
In Photoshop, when viewing the Print Dialog box, you are presented with several confusing but important decisions. Chief among these are selecting an “ICC Profile”, “Color Handling” and “Rendering Intent”. Without getting into a long discussion on Printer Setups and Printer Setting Options (which would probably be handled in another session), if you have Color Calibrated your Monitor and correctly set your Image’s Color Profile and Image Resolution for the size you are printing, you will want to (1) select the ICC Profile that best matches your Printer and Paper, (2) select “Photoshop Manage Colors” for Color Handling, and (3) select “Relative Colorimetric” for Rendering Intent.
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