What You Saw is NOT What You Got?

Consider the following scenarios. You are careful to set a proper white balance when you take the picture, then you come home, load up Photoshop (or the image editing program of your choice), and you get it looking perfect. Then you pirnt and something goes wrong - it looks like someone switched your files between the moment you press Print and you see the printhead moving back and forth creating an image. The results are just WRONG. Colors are different, the orange shirt is now salmon-colored, people are red-faced, a white dog is orange, the purple flower is now a bright shade of magenta, etc.

The immediate response is to go back to your image editor, or your printer dialogue and based on what you see in the print you start making adjustments - a little less magenta, a little more cyan, add some yellow - wasting tons of ink and paper in the process - and when its over you are wondering if your printer is broken.

Or, there is a different problem. Everything looks great on the screen, that cloudless blue sky is deeply saturated and perfectly smooth from edge to edge. You look at the print and it seems as if someone dropped coffee grounds during the print process. This is sensor dust. But there is a problem - you go back to the screen image and you can't see them. My guess is that you are using either a laptop or an inexpensive LCD/LED display with a limited bit depth. Without getting too technical, unless specifically noted in the specifications, all-purpose displays such as the sub $200 flat panels or those in laptops are not capable of displaying the more subtle gradations in tone and color. Sometimes his will come across as banding on a sky, where you have a very gentle shift in hue, saturation and luminosity from horizon to the top of the frame. Other times minute dust particles may have settled on your camera's sensor and blocking the light getting to the sensor directly beneath the particle, causing a "dust shadow" to appear. But in the bargain monitors, the bit depth is not enough to differentiate the subtle changes, making the dust spots invisible on the display. Most printers have a wider gamut, and are able to print this information,  The better the printer, the better the ablilty to display everything that is in the image - including the dust spots. Here is an example of dust spots:

If you don't see the dust spots, then there is a good chance you have one of "those" monitors. If you are serious about image quality, either sending it to others electronically or making a print - then its probablay a good idea to put a replacement display into the budget.

Well, as far as the first situation is concerned, there's an app for that. More accurately, there is a combination of hardware and software that you can purchase to address the difference between displayed vs printed colors and tones. There are a class of products called monitor/printer profiling applications that will fix the majority of the issues. These consist of a either a colorimeter or spectrophotometer that measures your monitor's native colors and gray tones on a test pattern, then creates a table of values that correct the differences between what the monitor shows and what the neutral standard is, and then builds a monitor profile that loads when you start your computer, making all the necessary adjustments. this way a green on screen will look like the green that will be printed - more or less. It's hard to do any image editing and color correction without at least the display being calibrated.


With the color accuracy of your display now under control, you have to address the print. If you use a printer manufacturer's inks and paper (and printer profiles if provided), or if you use a printing service. you are likely to get decent results - not perfect by any means, but reasonable. Most inexpensive printing services will use a hybrid technique, employing a digital projection onto silver halide emulsion paper, then processed in conventional wet process chemistry.  The more expensive houses will use high quality, color profiled and calibrated inkjet printers. Each paper type offered will have its own profile. the printers will use anywhere from 8 to 12 different pigmented inks - providing the widest color gamut and dynamic range possible. Very few affordable processes can even begin to approach the quality obtained from a properly processed inage printed on a 12 color image printed on rag paper in a color managed workflow.




Spyder Studio with monitor and printer profiling

Luckily the tools used to do this at the pro or commercial level are available in scaled down versions for the consumer. Datacolor and Xrite both offer affordable profiling solutions that work with most displays and printers as well as more expensive ones for professional printers and photographers. These create profiles for either printers or displays, or both.

The dust bunny situation involves being able to see the dust before you print. This requires using a display that is capable of showing dust.  At the present there are only a handful of displays that can do this - those which use e-IPS, S-IPS, P-IPS, H-IPS, AS-IPS, H2-IPS and UH-IPS. IPS stands for In Plane Switching, a display technolgy developed by LG Philips in 1996. LG makes nearly all the IPS panels currently available in the marketplace. For all intents and purposes the S, H and P-IPS panels are the ones to look for. The e-IPS is an adaptation of the technology to lower the cost, and more often than not can only display a color depth of 6 bits per color, or 2^6 x 2^6 x 2^6 = 64 x 64 x 64 = 262,144 colors simultaneously. This is not good for photo editing applications. The way 6 bit panels create 16.2 million colors is by rapidly switching between 2 colors at each pixel, creating the illusion of greater color depth - but while they look good for general applications, not being able to see all the information without switching is going to present problems seeing subtle things like dust and other artifacts. Sometimes you will see a panel specification stated in terms of a percentage of a color space. You might see something like 72% of sRGB. Most printers can now print close to 100% of sRGB, which means that the prints will show more color and tonal variation than your display, whicn in simple terms explains why you won't be able to see the dust bunnies on a $200 LCD/LED panel. With the exception of some Apple products and the Lenovo Thinkpad X220, nearly all displays are 6 bit.

The image below is an exaggeration, but a good way to illustrate the difference between high and low bitrate displays. The dithering is the switching that takes place - this is a static image, but you should be able to still see the banding. The rightmost color is typical of what you will see on an 8 bit (x3 = 24 bit) per color display.

At the very minimum you should be looking for a panel that can display 8 bits, or 2^8 x 2^8 x 2^8 = 256 x 256 x 256 = 16,777,216 simultaneous colors. These typically can display a color space as large as sRGB, considered the minimum for photo editing, and the pricier versions can display up to Adobe RGB, a bigger color space. A rule of thumb is to get the largest color space you can afford., but not less than 98% sRGB. The specs that are meaningless to you are speed, brightness, contrast ratio, etc. These are all well-beyond what you need. In some cases flat panel displays can be too bright, making it difficult to profile.

There are a few very costly 10 bit panels, which if you do the math,  2^10 x 2^10 x 2^10 = 1024 x 1024 x 1024 = 1,073,741,824 simultaneous colors. These are absolutely breathtaking, but be prepared to spend more than $1100 for a 27"panel. The problem with these is that unless you can create a 10 bit workflow, such a display is overkill. Most cameras are 8 bit, as are printers. There are few photo editors that can work in 10 bits. It is easy to see that  having a 10 bit panel would be unecessary.

You can find a list of popular IPS displays with street prices here . The ASUS PA238Q seems to be the least expensive 8 bit panel that offers full sRGB display at $300. I suggest that you look for reviews or a list of specifications for any display you are interested it to ensure that it is suitable for your purposes.



Once you are able to see stuff like dust spots, you need to be able to remove them, and there are two methods to accomplish this. Each has its good and bad points. The more conservatie but costlier approach is to send you camera in for a sensor cleaning. Give to someone else to do and if something gets messed up in the process, they will (hopefully) take care of things. This can cost from $50-$100 and you can be without your camera for several weeks.



dry and wet sensor cleanng system

You can always purchase a blower, dust brush and wet-cleaning swabs and solutions for around the lower price of sending the camera out. A blower and a brush,should be standard equipment, since the majority of sensor dust is removeable with these gentler tools. Use the mirror lock up function to expose the sensor, and using a light to see what you are doing, use a blower that is intended for this to gently blow the specs away. Sometimes you need to use a little "gentle persuasion" to get the more stubborn specs off. Under no circumstances should you use the compressed air products, which use unfiltered air, and can blast microgrit across your sensor, permanently etching it in the process. Actually, you would not etch the sensor itself, but the low-pass filter that is in front of it. In any case, you would be looking at a costly repair, typically in excess of $200.


If you are daring enough, you might try the wet method. This includes a swab of lint free material attached to a paddle that you dampen with a cleaning solution and wipe once across the sensor. Any time you touch the sensor you run the risk of scratching the filter, so you need to be super extra careful and resign yourself to the $200 or higher repair should things go wrong. I have done it 3x on my D200 with no damage, but everyone's mileage is different. If you at all nervous about this, just send it in.