Preparing Images for High-Quality Printing

Did you ever came back from a photo shop having printed some of your snapshots with the intention of framing them for display — but the result were so poor that you’ve decided to not continue and frame those?  “But those pictures looked okay on screen” you thought — and perhaps you thought maybe the photo shop wasn’t good enough and started to find another place to print your photographs.

What you probably miss is that a photo on print isn’t the same as a photo on screen.  A screen has its own light source but a printed photograph depends on ambient light.  Photos are made of a collection of dots — these are called pixels, short for “picture elements”  — and high-quality printers can produce higher density dots than screens — this is called “resolution”.  

Because of this difference, screens do not use the same method as printers to produce color.  Each pixel in a screen comprised of tiny red, green, and blue colored lights placed next to each other (these rarely overlaps one another on today’s LCD and LED displays).  However each dot in a printed photo comes from a mixture of cyan, magenta, yellow, and black ink droplets.

Likewise, most printers have higher resolutions than most screens.  Most mid-range inkjet printers today can produce 600 dots-per-inch (dpi) printouts.  However MacBook retina displays are only rated at about 220 pixels-per-inch and most other computer screens have lower pixel density values.  You probably didn’t notice the lower resolution when looking the photo at a screen.  However in the “real world” these low-resolution photos became grainy and — well — pixelated.

Large format photo printing

These are common problem areas that non-professionals encounter when producing images for high-quality printing:

  • color balance
  • resolution
  • noise

Color Balance Issues

Put simply when colors on the screen do not resemble the ones on the printed photo, then you have color balance issues.  This stems from the fact that screens uses lights and printers uses ink.  Screens use a combination of three light sources — red, green, and blue light emitters which corresponds to the three types of color cell cones in the human retina.  However since photographs rely on reflecting light instead of emitting, they use a mixture of four primary ink colors — cyan, magenta, yellow, and black — to provide colors for you to see.

Most photographic files are encoded in a format for use by displays — sequences of triplets containing the color values for red, green, and blue.  When printed, these values are translated into quartet of cyan, magenta, yellow, and black ink levels for every dot. As with every translation, there’s notably some loss that may occur. The loss in translation is even more pronounced when you consider that the color reproduction capabilities of prints is less than the colors that can be shown on-screen — despite printers typically have more resolution.

Color Space Comparison - sRGB and PrintIf you look at the diagram to the right comparing various color models (taken Wikipedia: Color Space), you can see that different output devices have their own ability in image reproduction.  You can see that the color range of “2200 matt paper” is not quite the same of sRGB — the latter being able to reproduce most of the color of the former except for a small portion.  But there’s an area in the magenta-blue-cyan area that even photo printers can’t reproduce.  Adobe RGB is a color model introduced by Adobe for use in its Photoshop software and some professional screens are engineered to cover this color range. These displays are often more expensive than regular “consumer” screens and sometimes sacrifices other aspects not related to color, such as response rates (i.e. these screens may show “ghosting” when the image rapidly changes).  Look for monitors advertised as “100% Adobe RGB” if you’re interested.  Display P3 screens — found in MacBook Pro 2016 and iPhone 7, among others — has a color range that falls somewhere between sRGB and Adobe RGB.

Thus keep in mind that photos which looks acceptable on-screen may look worse on paper. That is unless you take special care to cater for these differences and limitations.

Fortunately most color balance issues can be solved by the Auto Enhance feature of the Mac’s built-in Photos app.  Just try it out first and only do manual adjustments if that feature fail to enhance your photo automatically.

Also remember that if you have a True Tone display, you might want to deactivate the feature before making color adjustments.  This is to ensure that the colors you are looking at would look the same as what the staff at the print shop would see.

Photo Looks Too Dark

The most common color balance issue would be too dark.  Put simply, a dark image on screen would likely look even darker on print.  Remember that print works by reflecting light and reduces the light that it reflects — unlike a screen which has its own light source.

Fixing images that are too dark is quite simple using the Mac’s bundled Photos app. 

  1. Expand the Levels section to reveal the photo’s histogram.
  2. In the lower-right part of the histogram, click the rightmost handle and drag to the left.
  3. As you drag, the entire image should get lighter. Drag just until the rightmost part touches a peak in the right areas in the histogram.
  4. Check the photo — if it is bright enough, stop dragging. 
  5. If the photo looks over-exposed, drag that handle bit to the right until it “looks right”.

Image light adjustment

As you can see from the sample image above, the histogram is very skewed to the left and there’s almost no color on the upper quarter of the histogram. Adjusting the histogram to cover the full range makes the photo a bit brighter but not until it looks over-exposed.

Photo Looks Too Red

Camera flash can make light-skinned subjects to look pink or even bright red.  These overly red photographs may remind you of Technicolor films from the 1920s. 

Fortunately there’s an easy way to fix this using the Mac’s built-in Photos app. Just follow these steps after you have imported the photo into the app:

  1. Expand the “Selective Colour” section.
  2. Using the eyedropper tool, select a skin tone that is too red.
  3. Drag the “Saturation” slider all the way to the left. The skin color would change to gray-ish.
  4. Slowly drag the “Saturation” slider to the right until you get a natural-looking skin tone.

Adjust skin tone

Photo Looks Too Blue or Too Green

When skin tones looks grayish or greenish, it may be the case that it was taken in too much shade.  When sunlight doesn’t fall directly, the subject doesn’t get enough yellow color — and in outdoor daytime photographs, often there is no other light source than the sun.  Your camera may over-correct this and brought up the blue or green tints instead.

Adjust white point

Follow these steps to fix this using the built-in Photos app:

  1. Expand the Curves section.
  2. Select the rightmost eyedropper — this is to set the image’s white point.
  3. Click on an area that is supposed to be white.  In the same image above, the cigarette should be white.  You might need to zoom in to precisely point the correct pixel.
  4. You should notice that the blue cast vanish immediately

Washed Out

When the photo looks like it was printed on a T-Shirt that has been washed too many times, it’s likely due to color profile issues.  Either the image does not contain a color profile or it uses a color profile that the printer does not recognize.

A color profile describes how color values in the image file maps into intensity values of the respective output device — including print.  For example, the wattage needed to show a particular green color on one LED bulb may be different from the amount of power needed to show the same green color on another brand’s bulb.  Similarly inkjet printers have unique aperture sizes of their print heads and each would need different signal levels to produce the same color.  The process to ensure that these differing devices outputs the same colors given the same input image file is called color calibration — the result is a color profile for that specific device.  

Similar to all other calibration processes, color calibration is done against a well-known color profile — like how calibration of scales is done using a set of known counterweights.  A well-known color profile that is sRGB IEC61966-2.1 — or just sRGB for short — which is ratified by an international body and recognized by most manufacturers producing imaging devices. Other popular color profiles are Adobe RGB and Display P3.

By far the easiest way to ensure color accuracy is to embed a standard color profile in your image.  Don’t embed your display’s or your printer’s color profiles in your image since the photo shop won’t have your display or printer to calibrate upon.  Most photo printers and print shops supports the sRGB color profile and able to translate images with this color profile into their devices’ own profiles.  Unless you know any better (or a knowledgeable representative from the photo shop tells you otherwise), make sure that you have the sRGB color profile embedded in your image before handing it over for printing.  This way you’ll know what you see on display is going to be as close as possible to what you will get on print.

To see an image file’Color Profile information from Finders color profile, you can select the file from the Finder and then select “File|Get Info…” menu option or press “⌘i” . Expand the “More Info” section and the color profile is shown there, among other things.

You can use the built-in Photos app to convert images with other color profiles into the sRGB profile.  Simply import the image and then export it back out as JPEG or PNG.  Use JPEG for photographs and PNG for line-art images.  This would be useful for exporting screenshots in which the color profile would likely be “Color LCD” — the color profile of the display that the screenshot was captured in — hence not a standard color profile.

Resolution Issues

By far the most common mistake amateurs make when printing photographs is that they provide originals having less resolution than required. This is understandable since amateurs often do not have the proper knowledge of printing and the required printed size.

Printed images are made up of colored dots.  When there are more dots that can be placed within a given area of paper, the image would look less grainy and it gets better up until the point that the human eye cannot identify the individual dots any longer.  Hence the resolution of a printed page is measured in dots-per-inch (dpi) which measures how many dots that the printer is able to place in a horizontal (or vertical) line that is one inch long.  (This could also be measured in dots-per-centimeters, but the Americans got there first and brought their unwavering preference to the Imperial measurement system with it).

For a printed page intended to be viewed at a distance of 12 inches (30 centimeters), it seems that 300 dpi is the standard resolution for color printing.  Prints with resolutions less than this would show obvious pixelation when viewed at the aforementioned distance by a human with perfect eyesight — whereas people with above-average eyesight may prefer higher resolutions.  There are more scientific definitions of this based on pixel-per-degree values, but laypeople should just stick to a ballpark figure of 300 dpi as a “standard minimum resolution” for printing.

Why is this important?  When making high-quality prints, you should not pass images at a lower resolution than the capability of the printer.  When you do, you are missing the opportunity of getting the best quality possible and you risk producing grainy prints.

When you are printing a photo album, book, or anything that is intended to be viewed at normal reading distances (around 30 cm to 60 cm), it is important that you provide image files that are at least 300 dpi.  Measure the longest extent (the bigger width or height value) of the image in pixels and divide that by the desired print dimension in inches.  Make sure that the ratio is at least 300 pixels for every inch.

Most photo shops wants at least 300 dpi resolutions but some other prefer 600 dpi images.  However some printing companies can make do with lesser image resolutions — these companies either employ graphic artists who can enhance images for you or they do not know any better.  Please check with the print vendor for details and caveat emptor as usual.

I would not advise you to print photos downloaded from Facebook because it reduces images’ resolutions to just enough for display.  However since photo-prints typically needs higher resolutions than screens, you will likely get grainy results when printing from Facebook photo albums.  When you would like to print a photo from Facebook, try asking the photographer for the original file that comes from the camera.  That way you will have the highest resolution to begin with.

The following lists some common photo sizes and the respective minimum pixel dimensions that should obtain a good result.  Use this list if you need to quickly determine whether an image file would have sufficient resolution for printing at the targeted size. 

  • “2R”, 2×3 in, 5.1×7.6 cm, 600×900 px
  • “3R”, 3.5×5 in, 8.9×12.7 cm, 1050×1500 px
  • “4R”, 4×6 in, 10.2×15.2 cm, 1200×1800 px
  • “5R”, 5×7 in, 12.7×17.8 cm, 1500×2100 px
  • “6R”, 6×8 in, 15.2×20.3 cm, 1800×2400 px
  • “8R”, 8×10 in, 20.3×25.4 cm, 2400×3000 px
  • “10R”, 10×12 in, 25.4×30.5 cm, 3000×3600 px
  • “11R”, 11×14 in, 27.9×35.6 cm, 3300×4200 px
  • “12R”, 12×15 in, 30.5×40.6 cm, 3600×4800 px

But what if you do not have sufficient resolution to begin with?  Maybe the image is a company logo of your small business but you lost the original vector-graphics version of the logo.  Maybe the originals are low-resolution — such as snapshots coming from camera-phones of early 2000s.  Maybe the only photo source comes from Facebook uploads but your friend cannot be bothered to send you the original version?

If you thought of using Preview to up-scale the image, please refrain from doing so.  Most graphics software (including Preview) uses simple algorithms such as linear interpolation to resize images.  These simple algorithms are fast and are quite good when you just need to zoom into portions of an image.  However they tend to produce blurry or blocky upscaled results.  When you increase the resolution using these simple algorithms, the printed results would unlikely to be better than if you handed over the lower-resolution image to the printing company.

When you need to enlarge photos or line drawing images for high-quality printing, you need Bigger Picture.  This is an application that uses artificial intelligence to re-draw your image to increase its resolution without making blurry or blocky results.  Using Bigger Picture to enhance images is similar to hiring a graphics artist to up-scale images and then retouch it to remove any blurriness which came out of the enlargement process — but at a fraction of the cost.  However, if you are a graphic artist yourself, you could use Bigger Picture as part of your image enhancement workflow that would save you a significant amount of time retouching the output of a bicubic interpolation process.

You can follow these steps to use Bigger Picture to prepare an image for high-resolution printing:

  1. Load the image into Bigger Picture.
  2. Choose the “Printable” image enlargement mode.
  3. Specify the printer’s resolution (or if you are handing this to a photo shop, ask them what would be the recommended resolution).
  4. Notice that the image dimensions are shown both as pixels and as real-world measurements (in centimeters or inches, depending on your system’s Language and Region settings).
  5. Move the slider until the shortest side of the image matches with the desired length in real-world dimensions.  Using the shorter side would ensure that the image would exceed the minimum pixel size requirements.
  6. In the “Styles” radio buttons, select “Photo” if the image comes from a photograph or a photo-like graphic with rich gradations.  Select “Artwork” for logos, cartoons, or comic images.
  7. If the image came from a low-quality JPEG file, select the appropriate noise reduction option.
  8. Render the image to get the higher-resolution version.

Bigger Picture print enlargement

Compression Noise

When printing photos from downloaded from the web, you also need to pay attention for noise caused by data compression.  JPEG is a lossy compression algorithm — meaning that some data gets intentionally lost in the compression process with no way to get them back in the resulting image.  The stronger the compression setting, the resulting file would be smaller at the expense of more data getting lost.  When the algorithm drops too much data, the compressed image would have ringing pattern (similar to water drops) around contrasting areas of the image.  These ringing patterns are called JPEG compression artifacts or alternatively JPEG compression noise because they are introduced by the compression process.

JPEG Compression Artifacts Comparison 2x

Fortunately Bigger Picture is able to remove most JPEG compression noise.  Again, this would be similar to handing over the picture to a graphic artist to “cure” the image — selectively paint the areas in which the noise are clearly visible and either use a clone tool or in-painting tool of photo editing program to “erase” the noise using pixels around the affected area.  However the process is completely automated using BiggerPicture’s artificial intelligence algorithm.

Follow these steps to remove JPEG compression artifacts using Bigger Picture:

  1. Load the image into Bigger Picture.
  2. In “Style” select the image type — use “Artwork” for logos or other line-drawn image, including scanned comic books.  Use “Photo” when the image comes from a photograph or otherwise has rich gradations.
  3. In “Noise Reduction” choose the appropriate reduction level as according to the JPEG image quality — the lower image quality would call for greater noise reduction.
  4. If the image is already at the desired size, select the “Multiples” enlargement mode and select 1x enlargement (meaning no enlargement).  Therefore Bigger Picture would retain the original image’s dimension and dots-per-inch attribute.
  5. Render the image

Bigger Picture noise reduction settings

Anything Missing? 

That is all the tips from me on bringing an image from the digital realm into the physical world.  Please let me know your experience in applying these and whether there are any important aspect of photo-printing that I did not cover.

Until next time, take care.

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