GNOME Bugzilla – Bug 315285
Opened JPEG image very grainy (pixelated)
Last modified: 2008-01-15 12:59:54 UTC
USE GIMP for Windows Open a 72dpix72dpi JPEG file with GIMP. Now open the same file with windows picture viewer (or any other program) If you compare the two you find that the GIMP display is very grainy (pixelated) compared to the windows viewer display.
Most developers don't use windows. Please attach screenshots illustrating the problem.
Created attachment 51824 [details] screen shot of jpeg loaded in GIMP
Created attachment 51825 [details] Scren shot of jpeg in windows viewer
Unfortunately taking a screen shot seems to reduce the grain effect in GIMP a little but it is still quite easy to see the difference between the two pictures.
It looks as if the image viewer is filtering the image to be smoother, while GIMP shows it as-is. Would you mind attaching the jpeg file itself so we can verify this?
Created attachment 51828 [details] Original jpeg Here is the original.
The attachments in comments 2 and 3 both seem to be showing zoomed views of the file attached in comment 6. So all that is happening, I think, is that GIMP is using a different method to zoom the view -- and this would not be a bug.
Well, picture viewer blurs the image a bit to make it more pleasant - something that's appropriate for an image viewer, but not for an image manipulation program like GIMP. Zooming in to the maximum in both Picture Viewer and GIMP should reveal identical results.
The problem is only due to the fact that the GIMP does not do any interpolation in the zoomed-out view. This has already been reported in bug #76096. *** This bug has been marked as a duplicate of 76096 ***
This looks like a zoomed-in view, not a zoomed-out view. I don't think this is a bug at all, but whatever it is, it is not a dup of 76096. Re-opening and setting to NEEDINFO accordingly.
I created the zoomed-in shots to show the problem more clearly. The same grainy look can be observed in normal view. To me it seems that GIMP just displays se image different from windows picture viewer.
In that case, comment #8 is probably the correct explanation. You made this very difficult to deal with by zooming those shots, though -- any fractional zoom involves interpolation, so you are forcing us to compare degraded views instead of comparing the originals. Anyway, removing NEEDINFO for the moment.
Aren't you confusing zoomed-in and zoomed-out? The original JPEG image that you have attached is 1840x1232. I doubt that you have a screen that is large enough to display the image without zooming out, so I assume that the GIMP had opened it at 75% or 50% zoom or something similar. It is a well know fact that the GIMP does not resample the image when zooming out - instead, it simply omits some rows and columns. With a noisy image such as the attached JPEG image, the omitting some rows and columns may make the noise even more apparent, while resampling (averaging several pixels) will hide some of the noise. So your image would look better if the GIMP would resample the pixels as suggested in bug #76096. To check if this is really the problem or not, please compare the image in the GIMP at 100% zoom (not the default which may be smaller depending on the size of your screen) and the image that you see in the Windows picture viewer at the same zoom level. I don't know how the option is called in the picture viewer, maybe it is "original size" or "dot-for-dot" or something like that. You could also try to zoom in even further in both programs and compare the results, as suggested in comment #8. If the differences are only visible when the image is zoomed out, then this is definitely a duplicate of bug #76096.
Raphael, could you please actually *look* at the attachments in comments 2, 3, and 6, instead of speculating? The ones in comments 2 and 3 show *zoomed-in* views of a *part* of the original image.
There is obviously no difference in the image display except for the fact that the image viewer interpolates the zoomed view. There might be other differences, the image viewer could for example apply a color profile embedded in the image or apply a color correction for the monitor. All of this is handled in other bug reports though. I don't think it makes sense to keep a bug report open that claims that GIMP does things differently than some other programs, especially if that other program is an image viewer and not an image editor. There is nothing surprising about that. Closing as NOTABUG.