Comparison - MrSID, JPG, JPG2000, GeoTIFF 24-bit and GeoTIFF 8-bit

There are times I wish to work with Landsat ETM+ imagery with attention to file size. Instead of 80 MBs of raster imagery, I would like to work with 4 MBs. Using Global Mapper Raster Image Export feature, I am able to get the imagery I need easily. The raster format I typically use is JPG2000. Let me share why.

Raster Comparison (1:300,000)

I did a comparison of different raster formats July 2007. My previous comparison was poorly constructed and explained. I always meant to redo it. So here it goes. The first composite shows a portion of a MrSID, JPG, JPG200, GeoTIFF 24-bit and GeoTIFF 8-bit. At 1:300,000 scale the images are visibly indistinguishable. One appears to be just as good as the other.

Raster Comparison (1:25,000)

At 1:25,000 scale, which is pushing the limits of the original image (MrSID format), the first 4 images are very similar in clarity. The GeoTIFF 8-bit image begins to lose color depth, as one would expect from 8-bit imagery as it uses fewer colors in its color palette.

Raster Comparison (1:8,000)

Raster Comparison (1:2,000)

Finally, lets push the images far beyond their intended usefulness. The three middle images, JPG, JPG2000 and GeoTIFF 24-bit are noticeably superior to MrSID and GeoTIFF 8-bit at this scale. It is at the 1:2,000 scale that pixel size difference shows up. The three middle images all carry the same sized pixels and range of colors. The GeoTIFF 8-bit image has the same pixel size as the middle images, but without the rich variety of colors. The MrSID image, our base image, has a larger pixel size. Its color palette is used to form the colors found in all of the other images.

Now for the kicker - size and number of files: MrSID - 80.4 MBs and 2 files; JPG - 21.5 MBs and 3 files; JPG2000 - 4.5 MBs and 3 files; GeoTIFF 24-bits - 121.8 MBs and 1 file; GeoTIFF 8-bit - 10.4 MBs and 1 file. Clearly, the JPG2000 packs the greatest image bang for your MBs. However, I understand that JPG2000 is not widely used. If you are able to use it, do so as it gives you quality imagery in a compressed package. If you are not able to use JPG2000 format and you do not require working at 1:50,000 or lower, the GeoTIFF 8-bit works quite well. I happen to prefer JPG as my second choice after JPG2000. At twice the size of GeoTIFF 8-bit imagery, it is still a reasonably sized file to work with in lieu of MrSID. GeoTIFF 24-bits is far too large compared to the other three raster formats. Last, but not least is the MrSID format. It is my base imagery. The four other raster images were derived from my Landsat ETM+ image in MrSID format.

Hopefully, this raster comparison is both informative and helpful. If nothing else, the raster comparison images are pretty slick composites giving you side-by-side visible examples of these 5 popular raster formats.

Enjoy!

Comparison - MrSID with JPG, TIFF 8-bit and TIFF 24-bit

Some time ago, I did a comparison of images taken from a Landsat ETM+ mosaic - JPG, TIFF and MrSID. I thought I knew what I was doing, but I didn't. Finally, after many months, I intend to right my wrong.

This comparison looks at images taken from a Landsat ETM+ mosaic (N-32-65_2000). It looks a whole lot better if you select the image and follow it to my Flickr EVS-Islands area. Look at these images full size (1280x1024). After studying them for a few minutes, you will be able to discern differences in colors and clarity of details. The master image is the Landsat ETM+ (N-32-65_2000) in MrSID format. The images derived from the master image are in JPG, TIFF 8-bit and TIFF 24-bit. TIFF images tend to be larger (MBs to KBs), sometimes much larger (GBs to MBs) than JPG images. All second sets of images use an effect found in Global Mapper called Anti-Alias. It smooths the pixels, using an industry standard algorithm. I prefer to map with this effect on, as it gives a smoother shoreline to follow when I digitize. On with the visual comparison.

MrSID and JPG

Tranoy Area NO - Landsat N-32-65_2000 (1-10,000) MrSID (L) JPG (R) without Anti-Alias

Tranoy Area NO - Landsat N-32-65_2000 (1-10,000) MrSID (L) JPG (R) with Anti-Alias

(Again - look at the full-sized images in Flickr EVS-Islands - select the image, in Flickr, select "All Sizes" and you will be viewing the image at it's original size of 1280x1024.)

JPG has noticeable loss of detail. When I look at the image without Anti-Alias, it appears fewer colors are used in the image creating the illusion of larger pixels. I use JPG when I post images, because the files are many times smaller in size (KBs vs MBs) and the clarity is sufficient for viewing.

MrSID and TIFF 8-bit

Tranoy Area NO - Landsat N-32-65_2000 (1-10,000) MrSID (L) TIFF 8-bit (R) without Anti-Alias

Tranoy Area NO - Landsat N-32-65_2000 (1-10,000) MrSID (L) TIFF 8-bit (R) with Anti-Alias

TIFF 8-bit is an improvement over JPG, but larger in size. The TIFF format is typically much larger in size. MrSID came about because of gigabyte sized TIFF images. MrSID format could shrink the TIFF images into something more manageable and viewable. That said, TIFF 8-bit gives a wider range of colors, doing a better job with subtle shading. The image is clear and almost as good as the original MrSID image. It is a good duplication of the MrSID base image.

MrSID and TIFF 24-bit

Tranoy Area NO - Landsat N-32-65_2000 (1-10,000) MrSID (L) TIFF 24-bit (R) without Anti-Alias

Tranoy Area NO - Landsat N-32-65_2000 (1-10,000) MrSID (L) TIFF 24-bit (R) with Anti-Alias

TIFF 24-bit is as good as it gets compared to the other two options (JPG and TIFF 8-bit). When viewing the original size image, it is difficult to distinguish between the MrSID image and the TIFF 24-bit image. The colors most nearly duplicate those found in the MrSID image. Clarity and sharpness of detail are a near mirror of the MrSID image. It is a solid reproduction of the MrSID master image.

If the size of the image doesn't matter, but the clarity of details is important, the TIFF options are far superior than JPG. However, if size of the image is of concern and the sharpness and clarity of details is not, go for the JPG.

Okay, I know that all of you image specialist are guffawing at my layman's descriptions. However, most of my viewers are laymen, and a few laywomen. They appreciate the non-technical descriptions.

Enjoy!