Scarab Darkroom

©2013 Kornél Lehőcz



Scarab Darkroom is a tool for quick viewing, converting digital cameras raw format files, and applying basic corrections to these photos. All editing is non-destructive; the original file is never modified. The program was designed with ease of use as a primary consideration, but you may want to quickly read through this manual anyway to make sure you don't miss any features.


The program's window is divided into three parts; the main window showing the actual image, the photo strip at the bottom, and the panel on the right. The panel on the right has three tabs: Directory, Adjustment, and Metadata. In the directory panel you can navigate to the folder, which has your raw files. The program will show thumbnails of the photos in the current folder at the bottom. When you switch to a new folder, the first image is loaded automatically. Simply click on the thumbnails to switch between images! You can save a copy of the current photo in JPEG format by clicking on the button with the disc that says Jpg (at the bottom left). These photos are saved into a subfolder called "Converted" by default. You can change the output path and other things in the Options dialog. You can also use the Save As… button to save the current picture into a folder of your choice. Here you can also choose between TIFF and JPEG output formats. You can delete pictures using the bin/trash can button.

Moving on to the right, you will find two arrow buttons , which allow you to rotate the image left and right. The circular arrow button will enter rotation mode, which allows you to turn the image at arbitrary angles. Clicking it again will leave rotation mode.

You can enter the crop mode using the crop button . A dialog will apear, where you can choose from pre-set aspect-ratios, and clear the current selection. While in this mode, you can select an area of the image, which should be saved in the final picture. Click the crop button again to leave crop mode! You can also drag the edges of the selection at any time to adjust the area.

The following buttons allow you to set different zoom levels. 1:1 will display the image at 100% zoom, 1:2 at 50% size. The next button will fit the image into the window. None of these modify the image, they are only for viewing the photo. You can also change the scale factor using the slider next to these buttons. The button with the triangular road sign with an exclamation mark will show you the over-exposed areas of the photo, which are clipped with the current adjustments. The clipped pixels will be marked red. You can toggle this on and off.

Adjustments tab

Basic adjustments to the picture can be applied in the adjustments tab. You can use the thin vertical scroll bar on the right if not all of the adjustment sliders fit on your screen. All adjustments are instantly stored in an .xmp file saved next to the raw file. If you use another application, which stores settings in Adobe XMP sidecar files, this is not a problem; the settings of the various programs can co-exist in a file. The adjustment controls are grouped in collapsible panels.

The exposure panel groups sliders, which have more or less to do with exposure. Their effects are mostly self-explanatory. Therefore I will only give a short overview here:

The first slider allows you to correct the brightness of over- or under-exposed photos (a feature sometimes also known as exposure compensation).

Contrast can be changed using the next slider. Lowering it brings all the colors closer to middle gray, increasing contrast distances colors from it (similar to how it works in other applications).

Recovery allows you to recover highlights. The raw file records information beyond what is white by default. These very bright parts of photos are clipped with the typical rendition of the photos. When recovery is fully applied, this information is squeezed into the range displayed by the monitor. A little more technical information: this basically changes the response curve from linear (rendered gamma corrected) to logarithmic, which acts more like film - it compresses the highlights. The different channels are not clipped at the same levels (after color corrections), there is an algorithm, which guesses the value of the missing channels.

The next slider allows you to change the black level if the blacks are not deep enough.

Fill light lets you bring out details in dark areas. The term fill light is usually used to refer to the usage of a flash to light a subject when the background is bright. This allows you to do something similar, although only globally to all dark parts of the image. (Note: this is similar to upping the Shadows in the tone curve controls, but not the same thing.)

The following panel groups the controls, which have to do with colors.

The first two sliders are for correcting white balance. You can adjust the color temperature with the first slider or by using the color picker to select a neutral gray part of the picture. Using the color picker adjusts the temperature slider. The second slider allows you to correct a green or purple tint. Temperature and tint are independent – i.e. they don't affect each other. Adjusting tint is usually not required for photos taken under natural lighting conditions. You can reset the original white balance by clicking on the camera icon.

You can shift the hue of the colors with the next slider. This is like rotating the color wheel. The following slider controls saturation of the colors.

Vibrance allows you to give your photos more vibrant colors. It increases saturation without over-saturating bright colors, it boosts less saturated colors more. This gives a more postcard style look (or one could also say a look similar to Velvia film). A setting of zero for both saturation and vibrance will normally give the most precise colors. Note that by default it is set to +30%. Human faces may appear too red if too much vibrance is applied.

In the premium version the Colors panel contains two sub-panels: Individual Colors and Split Toning.

In the first one you can adjust the hue, saturation, and luminance of individual colors. You also have the option to convert to grayscale here.

Split toning allows you to give a separate tint to bright and dark colors. The hue sliders allow you to pick the color of this tint, and the saturation sliders basically control the strength of the effect. You can shift what is treated as shadow and highlight using the balance slider. Split toning is applied after grayscale conversion, so it is also suitable for sepia-tone like effects.




The sharpness panel currently only contains one slider, which allows you to sharpen the image. You should view the image at 100% magnification to see its effect. Allow a little time for the image to update! Note that sharpening not only brings out more detail, but also enhances noise.

The paid version includes a Noise Filter. There is currently a single slider in this panel, which controls how strong this filter is applied. When an image is loaded, the noise filter starts working in the background. It may take a few seconds until it finishes, and this slider is usable. You should view the image at 100% size to see the effect. (The result of the noise filter is currently not shown when viewing the image at <50% size.) Also note that the noise filtering algorithm has its limitations - it cannot deal with extreme levels of noise. It's currently usable up to around ISO 6400 on full frame cameras, and ISO 3200 on cameras with APS-C size sensors.

The premium version also has Chromatic Aberration correction - for lateral chromatic aberration to be more specific. This optical error usually shows up as purple/green or blue/yellow outlines. This is the result of the lens not magnifying the various wavelenghts of light equally.

The program has two sliders, which allow correcting this. The R/G slider allows scaling of the red channel - this will correct the purple/green artifacts, and the G/B slider the blue channel, which allows fixing the yellow/blue miss-colorations.

You may see the edge of the image becoming miss-colored when you adjust these sliders. Don't worry about this! Only the real-time displayed version of this effect has this issue. When saving the image, this is handled correctly, your saved picture will not have a miss-coloured edge.


The tone curve section lets you boost highlights, brighten or darken the mid-tones, and bring out the shadow parts better or deepen them. Setting a slight S-shaped curve will lend your pictures a more filmic look. The curve can currently only be controlled with these three sliders.




Slider values can be edited by clicking on the number displayed next to them. The default value can be eset by double-clicking on the slider.

You can copy and paste settings using the first two icons on the left at the top of the adjustment tab (or using Ctrl-C and Ctrl-V). This also works across images, if you wish to apply the same settings to a group of photos; this is the way to do it. The original image can be reset using the left curling arrow icon, and you can reapply your adjustments using the right curling arrow. This allows you to compare the adjusted image with the original.

The cog-wheel icon will open the preferences dialog box. (see next section) You can make the application full-screen using the arrow icon in the top right. This will not hide the panels, but there is another full-screen mode, which does - push the SPACE button to toggle that!

At the bottom you can see an RGB histogram, which is updated as you make color adjustments. You can hide the metadata displayed over it by clicking on it. Below the histogram you can read the RGB values of the pixel below the mouse pointer. This is the value after all corrections.



Here you can select the target color space in the premium version. This is always sRGB in the free version. sRGB is recommended if you are putting your images on the web. This is what is widely used on PC monitors and on the internet. Adobe RGB has a wider gamut (it can represent some very saturated colors better), and may be advantageous for printing. If you choose Adobe RGB, make sure you embed a color profile! (and that where you print respects it - some kiosks may not) Note that many applications are not color managed, and other than sRGB images will appear wrong in these. So, generally just use sRGB, unless you need Adobe RGB for printing, and know that everything is correctly color managed on the way!

In the next box you can change the demosaic algorithm. Most current cameras use a Bayer pattern sensor. They only record red, green, or blue at each sensor site. Here you can choose between several methods for guessing the missing color components. The various algorithms differ in speed, the level of detail they bring out of the image, noise level, and the amount of artifacts they produce. "Scarab" is the highly optimized method originally developed for this program. ScarabX2 is a slower variant of this, which typically produces slightly better results. It is only available in the paid version. The other algorithms are taken from the open source DCRaw, and are not very optimized (ie. run slower).


Options dialog

The options dialog can be accessed using the Options button on the lower left. Here you can set where and how the converted images are saved. JPEG images are saved in a folder called "Converted" in the current directory (where the raw files are) by default. If such a folder doesn't exist there, one is created. The name of this folder can be changed here. You can also select a fixed existing folder anywhere on your drives. For this uncheck "In current directory", afterwards the directory selection button is enabled (…). There is also an option to append a prefix and a suffix to the output filename.

The image can be scaled during saving, you can specify the output size as a percentage of the original, or give the width or the height in pixels. The aspect ratio is always preserved.

JPEG quality can also be set in this dialog. Smaller value results in smaller file size, but more quality degradation. If you are still planning to work on the image in another package, TIFF format or 99% quality JPEG is recommended.

For TIFF, you can choose between 8 and 16 bit per channel accuracy (paid version only). 16 bit is recommended if you are planning to do more processing on the image in another application. LZW compression can also be set here. It only works in 8 bit per channel mode. This is not lossy compression. The only a reason to uncheck it is to be able to load the image in a program, which doesn't support compressed TIFF files.

You can also choose whether you want an ICC color profile to be embedded in the file. If you work in Adobe RGB space, it is important to embed the color profile. Most software assumes sRGB if there is no ICC profile in an image file.


Keyboard shortcuts

SPACE – Full screen preview. This also hides the user interface elements.

Alt+Enter – Full screen mode. This removes the window edges and the task bar. The program's user interface is still shown.

Ctrl+Left button – Holding down the control button allows you to rotate the image using the mouse or touch pad.

Alt+Left button – Holding down the Alt key lets you make a new crop selection.

Ctrl+C – Copy current image settings to clipboard.

Ctrl+V – Paste image settings from clipboard.

Left and right arrows - step between images.


System requirements

- Operating system: Windows XP, Vista, or 7 (Windows 8 untested)

- 2 GB or more memory is highly recommended. (1 GB may be enough on Windows XP with 10 megapixel images)

- Graphics chip with OpenGL 1.2 support.

- An Intel x86 compatible CPU supporting the SSE instruction set. (Intel Pentium III or newer, or AMD Athlon XP or newer)

(Any Windows PC made in the last 10 years is likely to meet the last two criteria.)



"Scarab Darkroom requires OpenGL 1.2 support. Updating your graphics drivers may solve the problem."

If you receive this error message, the most likely cause is that a hardware accelerated OpenGL driver is not installed on your system, or there is a problem with its installation. Any PC made in the last 10 years will almost certainly have a graphics chip, which supports OpenGL 1.2 acceleration. If the driver is not present, Windows has a software OpenGL implementation, but this only supports OpenGL 1.1. Scarab Darkroom requires 1.2 for correct operation. The solution is usually to download the actual graphics drivers for your system. If you have a laptop computer, you should look for these on the manufacturer's website, and search for the graphics or video drivers for your model. In case of desktop computers, you need to know the graphics chip's manufacturer (eg. nVidia, AMD), and look for the driver on their website.



Programming and design by Kornél Lehőcz.
Scarab Labs logo by Csaba Kémeri.
The program incorporates code from Dave Coffin's DCRaw. The software also uses the following toolkits and libraries: wxWidgets, Qt, Adobe XMP, FreeImage, Intel JPEG library.
Special thanks to Andrea Meixner for all her help and support, and to everyone who submitted suggestions and bug reports!