Well this is a tricky little number for people like me who are doing things with high resolution images. I am frequently combining high resolution scanned Retrolens stuff with other aerial images and running into some scaling issues. Basically if I have got a Retrolens image at a certain resolution and I have the aerial image from LDS at quite a different resolution then scaling the Retrolens image can have quite tricky outcomes if the scaling is significant.
I have of today been working with a high resolution image of a particular area and it's been scaled down to something like 15% of the original dimensions in each direction (resulting reduction in pixels is 2.2% of the original) and this results in losing a lot of resolution. Well the truth is there is not a lot that can be done about this because regardless of how many pixels there were in the original, the size of the pixels in the final image is preset by the original aerial image that I am overlaying onto, and therefore there is a considerable loss of detail. This resampling is hard to understand because the detail on the screen preview is so sharp from just scaling the original pixels to a smaller size and then we can see after doing the transformation that so much detail has been lost in the scale down.
To be able to preserve all of the original detail I would have to have the original layer much larger with a pixel size set in the world file for the Jpeg image as this is how a GIS works out what area to display a map tile over - it looks up the world file and that tells it where the upper left corner is and also the size of each pixel and it scales the tile to cover a certain amount of space on the canvas.
I am going to experiment with that as it does seem desirable to be able to scale the maps up to see all of that detail on the ground at certain levels so this means greatly scaling up the original image and then not having to scale down the retro image so much. Up until now it has been the reverse with scaling most retro images up in size, which is understandably a lot easier for the software to deal with and results in much less quality loss. However there is a lot more work in that and in part it entails redrawing the whole mosaic from scratch which is not something that is easy or straightforward but it looks like that is the way to go but it will be experimental and not a high priority to carry out.
