Histogram display error with byte type images

[bnelsonbr]

What is the bug or the crash?

Using QGis 3.16.4 I have two problems with improper histograms for any byte-type image, using the histogram dialog.

Steps to reproduce the issue

First, using any Landsat band of byte type data (single band image) with true data min = 0 and true data max =223, and no enhancement option applied in the symbology, and then computing the histogram in the histogram dialog, the histogram shows as strongly stretched image. The displayed histogram white point (the unstretched grey value that is saturated to 255) has been applied at approximately the median gray value of unstretched population of pixels such that about half of the image pixels are saturated in the histogram. However, the displayed image itself is correctly shown as unstretched (no enhancement applied).

Second - if I apply a new mininmum stretch value in the histogram dialogue, the displayed image does not respond.

Versions

QGIS version
3.16.4-Hannover
QGIS code revision
654e76b

Supported QGIS version

• I'm running a supported QGIS version according to the roadmap.

New profile

• I tried with a new QGIS profile

Additional context

This is same problem as in closed issue #43098 (Bug in histogram visualization for images of type "Byte" #43098)

[gioman]

Second - if I apply a new mininmum stretch value in the histogram dialogue, the displayed image does not respond.

@bnelsonbr 1 issue per ticket.

[gioman]

QGis 3.16.4

@bnelsonbr this is outdated, you must always test on the latest point release available.

[gioman]

First, using any Landsat band of byte type data (single band image) with true data min = 0 and true data max =223, and no enhancement option applied in the symbology, and then computing the histogram in the histogram dialog, the histogram shows as strongly stretched image. The displayed histogram white point (the unstretched grey value that is saturated to 255) has been applied at approximately the median gray value of unstretched population of pixels such that about half of the image pixels are saturated in the histogram. However, the displayed image itself is correctly shown as unstretched (no enhancement applied).

@bnelsonbr unclear to me how to replicate, can you provide a series of steps and sample data?

[github-actions]

The QGIS project highly values your report and would love to see it addressed. However, this issue has been left in feedback mode for the last 14 days and is being automatically marked as "stale".
If you would like to continue with this issue, please provide any missing information or answer any open questions. If you could resolve the issue yourself meanwhile, please leave a note for future readers with the same problem and close the issue.
In case you should have any uncertainty, please leave a comment and we will be happy to help you proceed with this issue.
If there is no further activity on this issue, it will be closed in a week.

[andremano]

Issue remains. See below the test environment:

QGIS version 3.21.0-Master
QGIS code revision de53894

[github-actions]

The QGIS project highly values your report and would love to see it addressed. However, this issue has been left in feedback mode for the last 14 days and is being automatically marked as "stale".
If you would like to continue with this issue, please provide any missing information or answer any open questions. If you could resolve the issue yourself meanwhile, please leave a note for future readers with the same problem and close the issue.
In case you should have any uncertainty, please leave a comment and we will be happy to help you proceed with this issue.
If there is no further activity on this issue, it will be closed in a week.

[github-actions]

While we hate to see this happen, this issue has been automatically closed because it has not had any activity in the last 42 days despite being marked as feedback. If this issue should be reconsidered, please follow the guidelines in the previous comment and reopen this issue.
Or, if you have any further questions, there are also further support channels that can help you.