Fie on Photoshop: Krita, the Real Photoshop Killer

By: Carla Schroder
Thursday, February 7, 2008 01:10:34 PM EST
URL: http://www.linuxplanet.com/linuxplanet/reports/6459/1/

Photoshop Assassins

Two weeks ago we learned why Gimp, even though it is a superior cross-platform image-editing application, is not a "Photoshop Killer." I'm not fond of lurid headlines, but if I were to nominate a "Photoshop Killer" I pick Krita.

Krita isn't really going to kill anything or anyone. What it will do is meet most of the needs of users who want a modern, sophisticated native paint and image-editing application for Linux. It was designed from the ground up for graphics professionals. Unlike Gimp, which is constrained by its elderly 8-bit RGB graphics engine, Krita supports 8- and 16-bit CMYK, 8-, 16-, and 32-bit RGB, 8- and 16-bit YCbCr, 32-bit LMS cone space, 16-bit L*a*b*, 8- and 16-bit grayscale, and it even has a realistic Watercolors simulation. There is a lot of difference in subtlety and accuracy between the various bit ranges. At 8 bits you get 256 values per channel for color images, and at 16 you get 65,536. 32-bit RGB is really 24-bits per channel. The leftover 8 bits are either ignored, or used as a transparent Alpha channel; then it is called RGBA.

If you're shooting photos in RAW mode, modern DSLRs deliver 12- or 14- capture bit depth. To make a long story short, in real life you'll find that 16 bits gives you plenty of elbow room and excellent image quality.

Krita supports the PNG, TIFF, JPEG, Dicom, XCF, PSD, GIF, BMP, XPM, Targa, RGB, and OpenEXR file formats. It can import ICO files. PSD (the Photoshop file format) is only supported up to version 6, because starting with version 7 it became a closed format.

What Be These Color Spaces?

Krita supports more color spaces than any other FOSS application, which is good news for folks who want to go beyond good old RGB and CMYK. The various color spaces define different gamuts and different colors, so conversion from one to another usually means a loss of color fidelity. Some folks make themselves crazy trying to find a way to define colors precisely and objectively. But this is an impossible task because everyone perceives colors a little differently. 9-12% of men have a degree of red-green blindness, 1-2% cannot distinguish blue from yellow, and approximately 1% of women have some form of color-blindness. It's a master stroke of perversity that makes red and green so important in our culture, and a testament to inertia and indifference that they remain so.

But I digress. When you're editing your images you're either going for technical accuracy, or an emotional fidelity. That's where understanding the pros and cons of the different color spaces helps you to create your best and most pleasing images. While it's good to understand the different color spaces, the three you're most likely to use are RGB, CMYK, and L*a*b*.

The L in L*a*b* (also called LAB and CIELAB) stands for luminosity, and a and b are for the color-opponent dimensions. Using LAB calls for a fair bit of study. It encompasses a very wide color gamut, and you can apply sharpening, contrast, and color corrections that go far beyond what you can do with RGB and CMYK, because it separates color from detail. The a and b channels only define color. The L channel defines luminance, black-white, and brightness. The reigning guru of using LAB to repair and retouch digital images is Dan Margulis. This article, Color, Contrast, and L*A*B*, is an excellent introduction to what LAB is all about. Mr. Margulis is a Photoshop expert, but the same LAB principles apply to all image editors.

LMS, YCbCr, Grayscale, and Watercolors

The LMS cone color space aims to map colors to the physiology of the human eye, and its sensitivity at different light wavelengths. You remember from grade school (and this is the simplified grade-school explanation) how our retinas have rods for perceiving brightness and shapes, and cones for color. There are three types of cones: long wave, medium wave, and short wave, hence the name.

YCbCr is a special family of color spaces used in digital component video. Y is luma, or brightness. Cb and Cr refer to the chroma, or color signals. This was originally invented so that the same TV signals could be used by both black and white sets and color sets. It also allows colors to be re-sampled and compressed, and to balance brightness and colors to accomodate how the human eye perceives them. YCbCr isn't an absolute color space in the way that RGB, CMYK, and the others are, but is a way to encode RGB. There aren't any reasons I can think of to use the YCbCr profile when you're creating or editing still images, because it uses lossy compression and a small color gamut. If you want to separate brightness and hue, use LAB.

Grayscale is, well, no colors. Just black to white and all the grays in between. But a whole lot of grays- at 16 bits, you get 65,536 values per channel, which gives you a lot more accuracy and subtlety than the 256 values at 8 bits.

The Watercolor simulation has a 14-color palette, with different degrees of wetness and paint strength. LMS and Watercolor are not used in any ICC color-matching profiles, so don't make yourself crazy trying to find some.

The worlds of color spaces and color management are vast and complex, and now you know more than the majority of Photoshop users.

Resources