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index.md (4996B) |
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1 FAQ |
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2 === |
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3 |
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4 Why yet another image format? |
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5 ----------------------------- |
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6 Current image formats have integrated compression, making it complicated… |
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7 read the image data. One is forced to use complex libraries like libpng, |
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8 libjpeg, libjpeg-turbo, giflib and others, read the documentation and wr… |
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9 lot of boilerplate in order to get started. |
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10 |
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11 Farbfeld leaves this behind and is designed to be as simple as possible, |
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12 leaving the task of compression to external tools. The simple design, wh… |
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13 the primary objective, implicitly leads to the very good compression |
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14 characteristics, as it often happens when you go with the UNIX philosoph… |
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15 Reading farbfeld images doesn't require any special libraries. The tools… |
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16 just a toolbox to make it easy to convert between common image formats a… |
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17 farbfeld. |
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18 |
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19 How does it work? |
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20 ----------------- |
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21 In Farbfeld, pattern resolution is not done while converting, but while |
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22 compressing the image. For example, farbfeld always stores the alpha-cha… |
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23 even if the image doesn't have alpha-variation. This may sound like a bi… |
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24 at first, but as soon as you compress an image of this kind, the |
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25 compression-algorithm (e.g. bz2) recognizes the pattern that every 48 bi… |
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26 16 bits store the same information. And the compression-algorithms get b… |
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27 and better at this. |
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28 |
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29 Same applies to the idea of having 16 bits per channel. It sounds excess… |
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30 but if you for instance only have a greyscale image, the R, G and B chan… |
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31 will store the same value, which is recognized by the compression algori… |
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32 easily. |
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33 |
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34 This effectively leads to filesizes you'd normally only reach with palet… |
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35 images, and in some cases bz2 even beats png's compression, for instance… |
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36 you're dealing with grayscale data, line drawings, decals and even photo… |
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37 |
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38 Why use 16-Bits-per-channel all the time? Isn't this a total waste? |
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39 ------------------------------------------------------------------- |
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40 Not when you take compression into account. To make this clearer, assume… |
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41 paletted image with 5 colors and no transparency. So the data is only a … |
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42 regular chunks (color1, ..., color5) in a certain order. Compression alg… |
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43 have been designed to recognize those chunks and can even look at how th… |
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44 chunks interact. |
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45 |
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46 Local tests have shown that farbfeld easily beats paletted PNG-images. T… |
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47 yourself and look at the bzipped results! There is no need for special |
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48 grayscale, palette, RGB, 1-, 2-, 4-, 8-, 16-Bit subformats. Just use 16-… |
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49 RGBA all the time and let compression take care of the rest. |
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50 |
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51 Which compression should I use? |
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52 ------------------------------- |
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53 bzip2 is recommended, which is widely available (anybody has it) and giv… |
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54 results. As time will move forward and new algorithms hit the market, th… |
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55 recommendation might be rethought. |
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56 |
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57 Is metadata supported? |
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58 ---------------------- |
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59 |
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60 Almost every image format out there has special offsets or locations |
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61 where metadata is stored. In itself, there are several different metadata |
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62 formats (Exif, XMP, etc.). For farbfeld, to keep it simple, there are |
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63 no provisions within the file format for metadata. Instead, one can |
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64 use so-called sidecar files (also known as buddy files or connected |
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65 files). As an example, to provide metadata for an image.ff.bz2, one can |
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66 add a file called image.xmp that contains XMP metadata for said image. |
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67 |
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68 An added advantage of this approach is that the metadata is independent |
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69 of the image compression. As argued above, compression is vital for |
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70 farbfeld to be used efficiently, but when thinking of an application |
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71 that lists farbfeld-images in a folder, it might want to access |
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72 metadata as fast as possible. |
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73 |
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74 The use of multiple files for one entity is a downside, but it wouldn't |
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75 be a problem at all if modern file systems supported forks. |
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76 |
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77 What about NetPBM? |
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78 ------------------ |
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79 NetPBM is considered to be the most simple format around, however, there… |
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80 room for improvement. In fact, it doesn't help that the format is subdiv… |
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81 into Portable BitMaps, Portable GrayMaps and Portable PixMaps. It's not … |
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82 when a manpage can't give a simple overview of a format in a few sentenc… |
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83 |
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84 NetPBM's big vice is that it has originally been developed to be hand-wr… |
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85 and passed around as plain text. A binary format exists, but still handl… |
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86 optional comments in the header, base 10 ASCII width and height values, |
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87 arbitrary whitespace inside the data and out-of-band image size and colo… |
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88 is too painful for the sane user. |
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89 |
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90 Judging from the usage of the format considering how long it's been arou… |
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91 it's no surprise it never really took off. Additionally, functionality l… |
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92 alpha channels and 16-Bit color depth can only be achieved via extension… |
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93 to it being a textual format it also lacks the desired compression |
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94 characteristics. |
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95 |
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96 The question you have to ask yourself is: Can I read in a format without |
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97 consulting the manpages? If your answer is yes, then the format is simple |
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98 enough. In this regard, NetPBM can be considered to be a failed format. |
