What is meant by color space photography

Photo printing, image editingPatrick ZasadaComment

Before we get into any form of print preparation, the ultimate photo paper must be determined! Every photo paper requires a different and individual soft proof right from the start! Photo papers are sometimes extremely different and can contribute to a completely different image effect. The right choice of paper is therefore at least as important as the choice of lens. However, some papers have a slight inherent color or a special structure. To ensure that the printed photo comes as close as possible to the result on the screen, a correctly performed soft proof is urgently required. But first you have to choose a paper.

Calibrate the screen

Image printing places high demands on your own hardware and the correct handling of the print data. Anyone who has ever had pictures printed in a cheap drugstore knows the problem that the printed photos never look like they do on the screen. Often the pictures are far too dark or the colors too strong. Sometimes even a color cast can be seen which could not be guessed on the screen. Ideally, however, the images should look exactly the same in printed form as they do on the screen.

First of all, a good screen with a large range of colors is required for image processing. Cheap entry-level models are often not enough here. But even a high quality screen cannot be used just like that. Every screen must be calibrated regularly for the purpose of image processing. A calibration device such as the Spyder from Datacolor or the X-Rite Colorimeter is required for this. Put simply, it is a calibrated camera that is attached to the screen. The software supplied shows exactly defined color fields on the screen, which are measured by the calibration device. If color deviations are determined, a corresponding correction profile is stored in the computer, which guarantees correct color representation. The screen should be calibrated at night or in the dark in order to reduce the influence of interfering stray light during the measurement. Before calibrating the screen, the following basic settings should be selected on the monitor (Usually preset for laptops):

  • Color temperature 6500 ° Kelvin

  • Brightness approx. 100 candela / m²

  • Gamma 2.2

In the case of monitors that have not been calibrated, it can happen that they have a color cast or that the colors are too cold or too warm. The human eye gets used to it quickly, so this is hardly noticeable in practice. On a monitor that is too cool, the images are automatically subconsciously processed too warm, as this looks so halfway neutral on the screen. At the latest when they are printed, the images appear orange. However, the fault is not with the printer, but is due to a non-calibrated monitor. It is therefore important to calibrate the screen regularly and to commission a high-quality printing company, which in turn works with calibrated printers.

Set up ICC profiles & softproof

Note: The CMD ⌘ key on MacOS corresponds to the CTRL key on Windows and the ⌥ key option on MacOS corresponds to the ALT key on Windows.

Color changes cannot just be attributed to a poorly calibrated monitor. The type and composition of the photo paper also has a decisive influence on the representation of the image. A high-gloss direct print behind acrylic glass has a more intense color than a photo print on matt and slightly yellowish paper. In addition, very light shades of color can also have a slightly different effect, depending on the inherent color of the paper. The dark colors often appear less detailed on matte paper than on the screen. Ultimately, an image in printed form will never look exactly the same as it does on the screen, if only because the screen has an active white background lighting and the effect of the photo paper is heavily dependent on the ambient light. Nevertheless, the properties and color representations of certain types of paper can at least be simulated well with appropriate ICC color profiles. The high-quality providers, such as Whitewall, offer corresponding ICC profiles for downloading for every type of paper. This means that a so-called soft proof is possible in Lightroom or Photoshop. Before the final saving of the images, the soft proof should be activated for the simulation of the paper in order to make small color and brightness adjustments if necessary. Just as there is a light warning function when taking photos in the camera, a color gamut warning can be activated in addition to the soft proof. The view looks similar, here color areas that can no longer be displayed on the photo paper are highlighted by a color. Instructions for setting up such soft proofs can be found on the providers' websites.

Installation:

After the ICC file for the respective photo paper has been downloaded, it must be installed

MacOS: Double click on the file

Or profile file in the directory/ Library / ColorSync / Profiles copy

Windows: Right click → Install profile

Or file in the directoryC: / windows / system32 / spool / drivers / color copy

Setup in Adobe Photoshop CC

Restart Adobe Photoshop:

Open the file to be simulated: Menu → View → Set up proof → User-defined. Select the profile under "Device to be simulated".

The following settings are to be selected in the dialog window:

Note: With a few ICC profiles, these settings may differ. In rare cases it is recommended to render the profile perceptually. The recommended information can be found on the download page of the respective ICC profiles from the providers:

With the key combinationCmd +Y the soft proof is switched on and off. When the proof view is activated, the name of the photo paper and the name of the photo paper are shown in the top left of the work window. If the proof view is deactivated, the paper description is not displayed. With the key combinationCmd+Shift+Y the color gamut warning is activated or deactivated again within the activated proof view. All colors that can no longer be displayed on the photo paper are highlighted in gray. Usually this applies to particularly bright and saturated color areas; here the saturation or dynamics can be locally reduced and masked out.

Setup in Adobe Lightroom Classic CC

Restart Adobe Lightroom:

In order to be able to start the soft proof, it is necessary to switch to the "Develop" view. Below the picture we find the following dialog window:

In the toolbar we tick Softproof. If this bar is not available, we go to View → Show toolbar or we press the shortcutT. Alternatively, the sooftproof can be activated using the shortcutS. can also be reached directly.

In the histogram itself there are two symbols at the top left and right. These places usually have triangular arrow symbols for the depth and light warnings. In the sooftproof view, the color range warning is hidden behind these symbols, which highlights those areas whose colors can no longer be displayed on the paper. Clicking on the icons activates the farm scope warning for the lights and / or shadows. In the image section on the left you can see that some dark green and light yellow tones are highlighted by blue (shadows) and red (highlights). This view is very reminiscent of the highlight warning, but only relates to the colors! If the soft proof is deactivated, the black and white points must be optimized separately:

If the softproof is deactivated, the triangular symbols can be used to highlight the highlights and black tones in the image. Areas with a blue background are therefore absolutely black and no longer contain any details, while the red areas now represent white values. If the soft proof is deactivated, the light warning can also be activated via the shortcutJ can be achieved. Both the light warning and the color gamut warning in the soft proof should be checked before each print. At the same time, it makes sense to simulate the paper color in order to be able to estimate whether the white balance may need to be adjusted or whether the image on the paper could possibly appear a little darker.

8 bit vs. 16 bit image processing

Important NOTE:The camera should take pictures in RAW, i.e. in the raw data format. However, there are still various setting options here. Use lossless compression to get the best quality. But the choice of the right color space is also relevant. 14-bit lossless compressed RAW in ProPhoto- or Adobe RGB is the setting we should choose to get the maximum of colors and dynamics. However, the entire image processing process should also work in the largest possible color space and with a high bit setting (e.g. ProPhotoRGB in 16 bit). Only at the end of the image processing should the image be converted into the required format.

While the color space defines which colors can still be displayed, the color depth says how fine the differences between the nuances per color channel can be. The larger the bit specification, the more gradations are possible. A bit consists of a pair. If we wanted to display a brightness gradient from black to white in the 1-bit color space, we would only have two colors available, namely black and white. With 2-bit the course would run from black to dark gray to light gray and finally to white, etc. The number of individual gradations per color channel is calculated using powers: 8 bits could also be represented as 2 ^ 8; this corresponds to 256 gradations per color channel. Since red, green and blue (RGB) have a total of three color channels from whose superimposition all other colors can be represented, we come to (2 ^ 8) ^ 3 or 16.7 million possible colors. With 16 bit, on the other hand, there are even 280 trillion colors, which is 17 million times as many. All reserves are required for image processing. The more information is available, the higher the dynamics or the tonal range of the image. In this way, bright areas of the image can be darkened, while very dark areas can be clearly lightened without the image quality being visibly reduced. With these settings, modern cameras can cover a dynamic range of 12 to 15 f-stops, depending on the camera model, with each individual f-stop halving or doubling the brightness. With the correct exposure, the darkest point in the image can be 2 ^ 15 or approx. 30,000 times darker than the lightest point in the image. Even then, with optimal exposure, all structures would still be registered that could be darkened or lightened if necessary without a visible loss of quality. At least this is the case in theory, since the lens usually represents the bottleneck in the system and limits the effective color depth and tonal range. With particularly good fixed focal lengths, it is possible to get relatively close to the performance of the sensor. In this respect, the best settings should be selected here, even if they cannot be fully exploited with every lens.

THE 16-BIT PROBLEM: RESTRICTED FILTERS IN PHOTOSHOP

Some Photoshop functions, such as HDR toning or some filter effects (in older versions of the oil filter) unfortunately only work in 8-bit edit mode. Should the Photoshop document be reduced to 8 bits in this case? No, because the filters can also be used differently. To do this, the corresponding layers must be converted into a smart object. The layers packed in the smart object can now be reduced to 8 bits and edited accordingly without reducing all layers or the entire document.

Color spaces (sRGB, Adobe RGB, ProPhoto RGB & CMYK)

As can be seen in the figure, the color spaces vary in size. In order to be able to display as many colors as possible and thus achieve the best quality, the largest color space must be selected. Normally this is the ProPhoto or Adobe RGB color space for all common cameras. Although most web applications can only display the sRGB color space, since the sRGB color space is only a subset of the larger ProPhotoRGB color space, it can be converted into the smaller color space without any loss. However, it does not work the other way around. Especially if we plan to print the pictures later and we also have a lot of blue and green tones in the picture, it is a great advantage to have worked with the ProPhoto RGB color space from the outset. Incidentally, the CMYK color space is the smallest of all common color spaces.

For image processing it makes sense to work in the ProPhotoRGB color space and 16 bit color depth in order to obtain the greatest reserves. Only at the end can the photo be compressed to a smaller color space required for printing. The default sRGB color space can be used for photos for the Internet. When printing, however, the best quality cannot be achieved, and unwanted color changes can also occur here. Concerning the color space you should consult with the responsible printer. For example, at Cewe-Print, the print data is required as a PDF file in the CMYK color space for brochures and exposés. Editing in CMYK is not possible in Lightroom, but the images can be converted from RGB to CMYK in Photoshop under the Image and Mode dialog. A slight change in color is visible. Therefore it may be necessary to carry out small final color corrections after the conversion. The image file can either be saved directly as a PDF, alternatively a TIFF can also be exported or the Photoshop files can be imported into Adobe Indesign to create a synopsis.

If, on the other hand, the photos are not put in a brochure but as an excerpt on photo paper, it is not necessary to convert their color space with the provider Whitewall, for example. Under the export settings, however, a better quality than sRGB should be selected. In this regard, ProPhotoRGB offers the best image quality. This should be saved as a 16-bit TIFF file. In order to keep the file size below one gigabyte, ZIP compression can be activated in the export and the layers should also be discarded for saving. File sizes of 200MB are not uncommon. For multi-page photo products such as calendars or photo books, the sRGB color space is prescribed by many providers.

Presets in Lightroom and Photoshop

The entire image processing should take place in ProPhotoRGB and 16Bit, so that all reserves can be used and when subsequent color adjustments and color filters are used, there is no podium formation (tone value breaks). So that we don't make any mistakes here, the default settings should be adjusted.

Lightroom: If we only work in Lightroom and do not intend to switch to Photoshop at the end, we do not need to worry about the settings. Lightroom automatically works in the best possible quality and only reduces the color spaces and bit depths at the very end, when the photo is exported.

However, if we have to do the final polishing or retouching in Photoshop, it is important that Lightroom transfers the images correctly to Photoshop or another program. For this we go to Lightroom Classic (Settings) → Preferences → External Editing and set the following values:

At the same time, it must be ensured that Photoshop accepts the transmitted data without an error message appearing every time. In Photoshop we click on Edit → Color Settings and define the working color space as follows:

These presets are optimized for printing high quality photos. When viewed on the web, images with ProPhoto RGB can suddenly look very strange. It is therefore important to remember to convert the photos to sRGB at the end of the image processing, if they are to be shown on the Internet or the printing requirements are different. So that this is not accidentally forgotten, it is advisable to use a corresponding one action to be created for saving.

Resolution & DPI

Usually the images are printed with a pixel density of 300 dpi. The DPI setting is irrelevant for images for the web, as the overall resolution is important here. The unit DPI only comes into play when a certain image size is fixed, as is the case with printing. The abbreviation DPI stands for "dots per inch". This is the specification of a pixel density, which initially has nothing to do with the image size. An image with a very low resolution of 30 x 20 pixels can easily have over 300 dpi if it is only printed 2.5 millimeters wide.The DPI number tells you how high the resolution of the image must be in order to achieve a certain image size. To do this, you first have to convert from centimeters to inches. One inch is equal to 2.54 centimeters.

The front page of an A4 brochure is 21 x 29.7 cm, which is 8.27 x 11.69 inches. In order to be able to print a photo in A4 format full-page with a point density of 300 dpi, an image width of 8.27 "x 300 dpi = 2,481 px and an image height of 11.69" x 300 dpi = 3,507 px. An image resolution of 2,481 x 3,507 px is required for an A4 page, which corresponds to a resolution of 8.7 MP. The image should be reduced and sharpened accordingly before saving.

How big the picture should actually be in the end has to be agreed with the printer. Many brochures can be printed with a maximum of 220 to 250 dpi, while 400 dpi is still common for photo paper. On the other hand, the DPI is also related to the viewing distance. Posters that should be viewed from a distance of 10 meters often have point densities of less than 20 dpi.

Without additional information related to the final dimensions, DPI information alone is completely meaningless, as no information about a meaningful image resolution can be derived from it. For this reason, no dpi information is required for web applications, as the final image size depends on the website visitor's monitor. The actual image resolution in pixels is more relevant for this. The dpi number does not say anything about the image quality either. If we set up a FullHD or 4k projector, the image size and thus the DPI number varies with the distance to the screen. The resolution or quality, however, does not change (if you disregard the brightness). Although projectors, strictly speaking, do not speak of DPI, but of PPI (pixels per inch), the principle is actually the same. If you are not sure which DPI is exactly required or how to set it correctly, this can be neglected in an emergency. If you provide the image in the maximum available resolution, you are usually on the safe side, since most manufacturers adjust the size of the print data (except for PDFs) themselves.

A correctly set image size, taking into account the DPI, however, has a small advantage: the subsequent sharpening of the images is easier. The difference is honestly only visible to the trained eye and shouldn't be noticed by most laypeople anyway.

Sharpening and final adjustments

Convert to the correct color space or the correct color profile

Before the photos are scaled, it is necessary to convert them to the correct color space. Depending on the printing company, there are different requirements here. For single image products such as murals from Whitewall, the images can remain in the ProPhoto RGB or Adobe RGB color space and do not have to be downscaled. Photo booklets or calendars from SaalDigital, on the other hand, have to be converted to the smaller sRGB color space and for flyers or magazines from Cewe-Print it is necessary that the print data is in CMYK. The exact requirements can always be found on the website of the respective provider.

Immediately before the color profile conversion, a summarized layer should be created, otherwise the appearance may change in some cases. For this we need the key combinationCmd+Shift+option+E.

To convert the color profile, click in Photoshop on Edit → Convert to Profile ... Now the following dialog window opens:

When converting color spaces, there may be slight color shifts and the image changes its appearance slightly, since not all colors can be displayed in the smaller color space. After the color profile conversion, small color and contrast adjustments should be made if necessary. The setting levels selective color correction, color balance, hue / saturation, dynamics, brightness / contrast, gradation curves and exposure can help here for fine-tuning. The soft proof should be activated with the respective ICC profile and the color gamut warning should also be observed. If the appearance fits so far, the image size can be optimized.

Change image size

Before the image size is adjusted, it may be necessary to cut the image to the respective image format in which it is to be printed. Toenlargement of the image we click on Image → Image size, the following dialog window opens:

Should the picture, however, be used for a brochurescaled down we choose customized settings:

Sharpen photos for printing

After the photos have been scaled to the correct size, they usually need to be sharpened. There are various sharpening techniques for this, which can also be combined with one another. Portraits should be sharpened a little differently than, for example, photos of modern architecture. Going into all the details here would go beyond the scope. Instead, only two very easy sharpening techniques will be presented:

Resharpening for matte paper:

We create withCmd+Shift+option+E. a new consolidated level. If this already exists, we will also duplicate it as an alternativeCmd+J. We now select this upper level and click under Filters → Other Filters → High Pass and select a radius from 0.9 to 1.0 px. Now we get an almost completely gray layer. We now set the gray layer from the “Normal” mixing mode to the “Copy into one another” mixing mode.

Resharpening for glossy paper:

We create withCmd+Shift+option+E. create a new combined level and duplicate itCmd+Jso that we get two new levels. We now select the upper level and click under Filters → Other Filters → High Pass and select a radius from 0.7 to 0.8 px. Now we get an almost completely gray layer. We now set the gray layer from the “normal” mixing mode to the “copy into one another” mixing mode and reduce the opacity to approx. 40-60%.

The second level from the top, directly below the high-pass level, we now have to sharpen twice: We click on Filter → Sharpening filter → Unsharp mask. In the dialog window we select a thickness of 60, a radius of 0.4 px and a threshold value of 1 and confirm with OK. Now we repeat the whole thing, but this time choose a strength of 200, a radius of 0.2 px and a threshold value of 0. In order to save time in the future, it makes sense to create these sharpening techniques as an action.

Saving Photos - The Right File Format