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The dynamic range (ratio between darkand bright regions) in the visible world far exceeds the range ofhuman vision and of images that are displayed on a monitor or printed.But whereas human eyes can adapt to very different brightness levels,most cameras and computer monitors can reproduce only a fixed dynamicrange. Photographers, motion picture artists, and others working withdigital images must be selective about what’s important in a scenebecause they are working with a limited dynamic range.
High dynamic range (HDR) images open up a world of possibilitiesbecause they can represent the entire dynamic range of the visibleworld. Because all the luminance values in a real-world scene arerepresented proportionately and stored in an HDR image, adjustingthe exposure of an HDR image is like adjusting the exposure whenphotographing a scene in the real world.
Merging images of different exposures to create an HDR image
A. Image with shadow detail but highlights clipped B. Imagewith highlight detail but shadows clipped C. HDR imagecontaining the dynamic range of the scene
It seems like HDR or High Dynamic Range imagery is all the rage right now. There are lots of tools around for assembling an HDR image and, although.
In Photoshop, the luminance values of an HDR image are storedusing a floating-point numeric representation that’s 32 bits long(32‑bits-per-channel). The luminance values in an HDR image aredirectly related to the amount of light in a scene. By contrast,non-floating point 16‑ and 8‑bpc image files store luminance valuesonly from black to paper white, reflecting an extremely small segmentof dynamic range in the real world.
In Photoshop, the Merge To HDR Pro command lets you create HDRimages by combining multiple photographs captured at different exposures.Because an HDR image contains brightness levels that far exceedthe display capabilities of a standard 24‑bit monitor, Photoshoplets you adjust the HDR preview. If you need to print or use toolsand filters that don’t work with HDR images, you can convert themto 16- or 8‑bpc images.
How many photos are required to process a quality HDR merge?
Read these guidance notes and tips by Rikk Flohr (Software Quality Engineer for Lightroom ecosystem of apps, Adobe).
HDR photos are used to capture scenes having a large dynamic range. However, using more number of photos can lead to unwanted artifacts from poor alignment or ghosting. For optimal HDR merge, the aim is to capture photos in a manner that each part of the scene is well-exposed, that is neither blown-out nor under-exposed in at least one of the photos.
Use the following guidelines to identify how many photos work best for your case:
- If your HDR bracketing is less than 3.0 stops in total separation (-1.5, 0, +1.5), use only the darkest and brightest exposures to generate an HDR. Capturing the middle exposure, or zero exposure, is not necessary for generating a quality exposure blend in such cases. If you exceed the 3-stop separation between the darkest and the brightest exposures, an additional exposure offset becomes necessary to process a good quality HDR photo.
Camera Bracket settings | Optimum number of exposures for merging photos to HDR |
---|---|
-1.5 to +1.5 | 2 |
-3.0 to +3.0 | 3 |
-4.5 to +4.5 | 4 |
-6.0 to +6.0 | 5 |
- If you are a photographer using the ± 1.5 exposure bracket, you can ignore the zero or middle exposure. This helps in faster render and improves alignment odds in the resultant HDR by reducing the chances of potential camera movement between the exposures. However, the zero exposure can be useful in scenarios where the capture scene is within the acceptable range of a single exposure and can be developed independently.
- If you are a standard HDR shooter using a ± 2.0 bracket, you ideally require only three photos to merge into an HDR.
- If you are a 5 shot ± 4.0 stop shooter, you can now drop from 5 shots to 4 shots for merging and processing HDR. However, if you are a 7 shot ± 6.0 stop shooter, you can now get the optimal HDR blend with only 5 shots (-6.0, –3.0, 0, 3.0, 6.0) provided your camera has three-stop stepping in the exposure bracketing function.
Tips to keep in mind when you take photos to be combined with the Merge To HDR Pro command
- Secure the camera to a tripod.
- Take enough photos to cover the full dynamic range of thescene. You can try taking at least five to seven photos, but youmight need to take more exposures depending on the dynamic rangeof the scene. The minimum number of photos should be three.
- Vary the shutter speed to create different exposures. Changingthe aperture changes the depth of field in each exposure and canproduce lower-quality results. Changing the ISO or aperture mayalso cause noise or vignetting in the image.
- In general, don’t use your camera’s auto-bracket feature,because the exposure changes are usually too small.
- The exposure differences between the photos should be oneor two EV (exposure value) steps apart (equivalent to about oneor two f‑stops apart).
- Don’t vary the lighting; for instance, don’t use a flashin one exposure but not the next.
- Make sure that nothing is moving in the scene. Exposure Mergeworks only with differently exposed images of the identical scene.
You can use the following tools, adjustments,and filters with 32‑bpc HDR images. (To work with more Photoshopfeatures, convert a 32‑bpc image to a 16‑bpc or an 8‑bpc image.To preserve the original image, create a copy with the SaveAs command.)
Levels, Exposure, Hue/Saturation, Channel Mixer, Photo Filter.
Note:
Although the Exposure command can be used with 8‑ and 16‑bpc images, it is designed for making exposure adjustments to 32‑bpc HDR images.
![Hdri Hdri](http://blog.gregzaal.com/wp-content/uploads/2016/02/1.gif)
Normal, Dissolve, Darken, Multiply, Lighten, Darker Color,Linear Dodge (Add), Lighter Color, Difference, Subtract, Divide,Hue, Saturation, Color, and Luminosity.
In the New dialog box, 32 bit is an option in the bit depthpop‑up menu to the right of the Color Mode pop‑up menu.
All commands including Fill, Stroke, Free Transform, and Transform.
Photoshop (PSD, PSB), Radiance (HDR), Portable Bit Map (PBM), OpenEXR, and TIFF.
Note:
Although Photoshop cannot save an HDR image in the LogLuv TIFF file format, it can open and read a LogLuv TIFF file.
Average, Box Blur, Gaussian Blur,Motion Blur, Radial Blur, Shape Blur, Surface Blur, Add Noise, Clouds,Difference Clouds, Lens Flare, Smart Sharpen, Unsharp Mask, Emboss,De-Interlace, NTSC Colors, High Pass, Maximum, Minimum, and Offset.
Image Size, Canvas Size, Image Rotation,Crop, Trim, Duplicate, Apply Image, Calculations, and Variables.
Pixel Aspect Ratio (Custom Pixel Aspect Ratio, Delete PixelAspect Ratio, Reset Pixel Aspect Ratio, etc.)
New layers, duplicate layers, adjustment layers (Levels,Vibrance, Hue/Saturation, Channel Mixer, Photo Filter, and Exposure),fill layers, layer masks, layer styles, supported blending modes,and Smart Objects.
RGB Color, Grayscale, conversion to 8 Bits/Channel or 16Bits/Channel.
Support for square and non-square documents.
Invert, Modify Border, Transform Selection, Save Selectionand Load Selection.
All tools in the toolbox except: Magnetic Lasso, Magic Wand,Spot Healing Brush, Healing Brush, Red Eye, Color Replacement, ArtHistory Brush, Magic Eraser, Background Eraser, Paint Bucket, Dodge,Burn, and Sponge. Some tools work with supported blend modes only.
The Merge To HDR Pro command combinesmultiple images with different exposures of the same scene, capturingthe full dynamic range in a single HDR image. You can output themerged image as a 32‑, 16-, or 8-bpc file. However, only a 32-bpcfile can store all the HDR image data.
HDR merging works bestwhen photos are optimized for the process. For recommendations,see Takephotos for HDR images.
- (Photoshop) Choose File > Automate >Merge To HDR Pro.
- (Bridge)Select the images you want to use and choose Tools >Photoshop > Merge To HDR Pro. Skip to step 5.
- Inthe Merge To HDR Pro dialog box, click Browse to select specificimages, click Add Open Files, or choose Use > Folder. (To removea particular item, select it in files list, and click Remove.)
- (Optional) Select Attempt To Automatically Align SourceImages if you held the camera in your hands when you photographedthe images.
- Note:If images lack exposure metadata, entervalues in the Manually Set EV dialog box.A second MergeTo HDR Pro dialog box displays thumbnails of the source images, anda preview of the merged result.
- To the upper right of the preview, choose a bit depthfor the merged image.Note:Choose 32 Bit if you want the merged imageto store the entire dynamic range of the HDR image. 8‑bit and (non-floatingpoint) 16‑bit image files cannot store the entire range of luminancevalues in an HDR image.
- To adjust the tonal range, see Optionsfor 32-bit images or Optionsfor 16- or 8-bit images.
- (Optional) To save your tonal settings for future use,choose Preset > Save Preset. (To later reapply the settings,choose Load Preset.)
Move the slider below the histogram to adjust the white point preview of the merged image. Moving the slider adjusts the image preview only; all HDR image data remains in the merged file.
The preview adjustment is stored in the HDR file and applied whenever you open the file in Photoshop. To re-adjust the white point preview at any time, choose View > 32‑Bit Preview Options.
Note:
The Camera Raw Filter does not work with 32-bit files in the following:
- Adobe Camera Raw 9.10
- Photoshop CC 2017
If you are using one of the above, see The Camera Raw Filter no longer works with 32-bit files to view workarounds for this issue.
HDR images contain luminance levels that farexceed the dynamic range that 16‑ or 8‑bpc images can store. Toproduce an image with the dynamic range you want, adjust exposureand contrast when converting from 32‑bpc to lower bit depths.
Chooseone of the following tone-mapping methods:
Adjusts HDR tonality by adjusting local brightness regions throughoutthe image.
Radius specifies the size of the local brightness regions.Strength specifies how far apart two pixels’ tonal values must bebefore they’re no longer part of the same brightness region.
Dynamic range is maximized at a Gamma setting of 1.0; lower settingsemphasize midtones, while higher settings emphasize highlights and shadows.Exposure values reflect f-stops. Drag the Detail slider to adjust sharpnessand the Shadow and Highlight sliders to brighten or darken these regions.
Vibrance adjusts the intensity of subtle colors, while minimizingclipping of highly saturated colors. Saturation adjusts the intensityof all colors from –100 (monochrome) to +100 (double saturation).
Displays an adjustable curve over a histogram showing luminance values in the original, 32-bit HDR image. The red tick marks along the horizontal axis are in one EV (approximately one f‑stop) increments.
Note:
By default, the Toning Curve and Histogram limit and equalize your changes from point to point. To remove the limit and apply more extreme adjustments, select the Corner option after inserting a point on the curve. When you insert and move a second point, the curve becomes angular.
Toning Curve and Histogram adjustment using the Corner option
A. Inserting a point and selecting the Corner option. B. Adjustingnew point makes the curve angular at the point where the Corneroption is used.
Compresses the dynamic range of the HDR image while tryingto preserve some contrast. No further adjustments are necessary;this method is automatic.
Lets you manually adjust the brightness and contrast of theHDR image. Move the Exposure slider to adjust gain and the Gammaslider to adjust contrast.
Compresses the highlight values in the HDR image so theyfall within the luminance values range of the 8‑ or 16‑bpc imagefile. No further adjustments are necessary; this method is automatic.
If images have different content due to movingobjects like cars, people, or foliage, select Remove Ghosts in theMerge To HDR Pro dialog box.
Photoshop displays a green outlinearound the thumbnail with the best tonal balance, identifying thebase image. Moving objects found in other images are removed. (Ifmovement occurs in very light or dark areas, click a different thumbnailwhere moving objects are better exposed to improve results.)
Note:
For a tutorial on the Remove Ghosts option, see this video. (Discussion of Remove Ghostsbegins at 3:00.)
Response curves indicate how camera sensorsinterpret different levels of incoming light. By default, the MergeTo HDR Pro dialog box automatically calculates a camera responsecurve based on the tonal range of images you are merging. You cansave the current response curve and later apply it to another groupof merged images.
- In the upper-right corner of the Merge to HDR Pro dialog box, click the response curve menu , and then choose Save Response Curve. (To later reapply the curve, choose Load Response Curve.)
Ifyou originally created a 32-bit image during the Merge to HDR Proprocess, you can later convert it to a 16- or 8-bit image.
- Open a 32‑bpc image in Photoshop, and choose Image >Mode > 16 Bits/Channel or 8 Bits/Channel.
- Adjust exposure and contrast to produce an image withthe dynamic range you want. (See Optionsfor 16- or 8-bit images.)
Adjust displayed dynamic rangefor 32-bit HDR images
Thedynamic range of HDR images exceeds the display capabilities ofstandard computer monitors. When you open an HDR image in Photoshop,it can look very dark or washed out. Photoshop lets you adjust thepreview so that the monitor displays an HDR image whose highlightsand shadows aren’t washed out or too dark. The preview settingsare stored in the HDR image file (PSD, PSB, and TIFF only) and areapplied whenever the file is opened in Photoshop. Preview adjustmentsdon’t edit the HDR image file; all the HDR image information remains intact.Use the Exposure adjustment (Image > Adjustments >Exposure) to make exposure edits to the 32‑bpc HDR image.
Note:
To view 32‑bit readouts in the Info panel, clickthe Eyedropper icon in the Info panel and choose 32‑Bit from thepop‑up menu.
- Open a 32‑bpc HDR image in Photoshop, and chooseView > 32‑Bit Preview Options.
- In the 32‑bit Preview Options dialog box, choose an optionfrom the Method menu:Adjusts the brightness and contrast.Compresses the highlight values in the HDR image so theyfall within the luminance values range of the 8‑ or 16‑bpc imagefile.
- If you chose Exposure And Gamma, move the Exposure andGamma sliders to adjust the brightness and contrast of the imagepreview.
- Note:You can also adjust the preview of anHDR image open in Photoshop by clicking the triangle in the statusbar of the document window and choosing 32‑Bit Exposure from thepop‑up menu. Move the slider to set the white point for viewingthe HDR image. Double-click the slider to return to the defaultexposure setting. Since the adjustment is made per view, you canhave the same HDR image open in multiple windows, each with a differentpreview adjustment. Preview adjustments made with this method arenot stored in the HDR image file.
The HDR Color Picker allowsyou to accurately view and select colors for use in 32‑bit HDR images.As in the regular Adobe Color Picker, you select a color by clickinga color field and adjusting the color slider. The Intensity sliderallows you to adjust the brightness of a color to match the intensityof the colors in the HDR image you’re working with. A Preview arealets you view swatches of a selected color to see how it will displayat different exposures and intensities.
A. Preview area B. Adjustedcolor C. Original color D. 32‑bitfloating point values E. Intensityslider F. Picked color G. Colorslider H. Color values
With a 32‑bpc image open, do one of the following:
- In the toolbox, click the foreground or background color selection box.
- In the Color panel, click the Set Foreground Coloror Set Background Color selection box.
The Color Picker is also available when features let you choose a color. For example, by clicking the color swatch in the options bar for some tools, or the eyedroppers in some color adjustment dialog boxes.
The lower part of the HDR Color Picker functionslike the regular Color Picker does with 8‑ or 16‑bit images. Clickin the color field to select a color and move the color slider tochange hues, or use the HSB or RGB fields to enter numeric values fora particular color. In the color field, brightness increases asyou move from bottom to top, and saturation increases as you movefrom left to right.
Use the Intensity slider to adjust thebrightness of the color. The color value plus the intensity valueare converted to 32‑bit floating point number values in your HDRdocument.
- Select a color by clicking in the color fieldand moving the color slider, or by entering HSB or RGB numeric values,as in the Adobe Color Picker.
- Adjust the Intensity slider to boost or reduce the color’sbrightness. The new color swatch in the Preview scale at the topof the Color Picker shows the effect of increasing or decreasingstops for the selected color.The Intensity Stops correspond inversely to exposuresetting stops. If you boost the Exposure setting of the HDR imagetwo stops, reducing the Intensity stops by two will maintain thesame color appearance as if the HDR image exposure and the colorintensity were both set to 0.If you know the exact 32‑bitRGB values for the color you want, you can enter them directly inthe 32‑bit value RGB fields.
- Sets the stop increments for each preview swatch. For example,a setting of 3 results in swatches of ‑9, ‑6, ‑3, +3, +6, +9. Theseswatches let you preview the appearance of your selected color atdifferent exposure settings.Select to adjust the preview swatches to reflect the currentexposure setting for the image. For example, if the document exposureis set higher, the new preview swatch will be lighter than the colorselected in the Color Picker’s color field, to show the effect ofthe higher exposure on the selected color. If the current exposureis set to 0 (the default), checking or unchecking this option willnot change the new swatch.
- (Optional) Click Add to Swatches to add the selectedcolor to the Swatches panel.
Youcan edit and add effects to HDR/32‑bpc images using any of the following Photoshoptools: Brush, Pencil, Pen, Shape, Clone Stamp, Pattern Stamp, Eraser, Gradient,Blur, Sharpen, Smudge, and History Brush. You can also use the Text toolto add 32‑bpc text layers to an HDR image.
When editing orpainting on HDR images, you can preview your work at different exposuresettings using either the 32‑Bit Exposure slider in the documentinfo area or the 32‑Bit Preview Options dialog box (View >32‑Bit Preview Options). The HDR Color Picker also lets you previewyour selected foreground color at different intensity settings,to match different exposure settings in an HDR image.
- (Optional) Set the exposure for the image. See Adjustdisplayed dynamic range for 32-bit HDR images.
- For the Brush or Pencil tools, click the foreground colorto open the HDR Color Picker and select a color. For the Text tool,click the color chip in the Text tool options bar to set the textcolor.The Preview area of the HDR Color Picker helps you select and adjust a foreground color in relation to different exposure settings in the HDR image. See About the HDR Color Picker.Note:By default, the Toning Curve and Histogram limit and equalize your changes from point to point. To remove the limit and apply more extreme adjustments, select the Corner option after inserting a point on the curve. When you insert and move a second point, the curve becomes angular.
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Adobe Photoshop creates HDR files from your bracketed images, as you would expect, smoothly and professionally. To generate high dynamic range images in Photoshop, follow these handy-dandy steps:
1Launch Photoshop, and (optional) open the bracketed photos.
You have the option of opening your bracketed images now — the ones that will be the source photos for creating HDR. You also have the option later to automatically select all open images to merge into HDR instead of navigating and selecting them yourself.
2Choose File→Automate→Merge to HDR.
The Merge to HDR dialog box opens, as shown. Add your source images using this dialog box.
3Choose source images as follows:
If the images are open: Click the Add Open Files button. If the images aren’t open: Choose Files from the Use drop-down list, and then click the Browse button. Navigate to the folder that contains the bracketed photos and select them.
If you add a photo you don’t want, select it after it appears in the Merge to HDR dialog box and then click the Remove button. To add all images from a folder: Choose Folder from the Use drop-down list, and then click the Browse button. Navigate to the folder you want and select it.
4(Optional) Select the Attempt to Automatically Align Source Images check box.
This option helps align details in images and is especially helpful for hand-held brackets. If you shot your images using a tripod, you might not need to align source images. If you see smeared details, ghosting from static objects, or what looks like a double-exposure, come back and select this check box.
5Click OK to continue.
Photoshop merges the files into an HDR image. If there is a question about the exposure values of the images, Photoshop displays the Manually Set EV dialog box, as shown. Enter the correct camera parameters in the Exposure Time, f-Stop, and ISO text boxes, or select EV and enter the value in the EV text box, then click OK.
When finished, the Merge to HDR dialog box reappears in a new form. A large preview window and the bracketed images appear on the left.
6Select the images you want to remove from the preview from the left side of the dialog box. Select them again to add them back.
This allows you to change the balance of the HDR file toward under- or overexposure. You should be well served by trusting in your brackets, but experiment if the fancy strikes you.
7Click the +/– buttons at the bottom of the dialog box to zoom in and out of the Merged Result image.
You can experiment with the source images and white point.
8To retain the most flexibility, choose 32 Bit/Channel from the Bit Depth drop-down list.
This allows you to save the resulting HDR file. If you set it to less (16 Bit/Channel or 8 Bit/Channel) and click OK, Photoshop automatically starts the HDR conversion process (Photoshop’s terminology for tone mapping) and reduces the bit depth of the image. If you don’t need to save the HDR file, selecting the bit depth saves time.
9Drag the Set White Point Preview slider left or right to alter the image’s exposure.
This is not a permanent change. You have the chance to review and finalize the image’s exposure during HDR conversion. This change shows up in the Exposure slider of the Exposure and Gamma method of the HDR Conversion dialog box.
10(Optional) If desired, load a camera response curve from disk by selecting the Load From File radio button and clicking the button.
You can also save the current camera response curve for use in later HDR projects by clicking the Save Response Curve As button. If you want to keep things absolutely consistent across a photo shoot, save the a camera response curve for the first set of images, and then load it for subsequent sets from the same shoot.
11Click OK to create the HDR file.
You’re done. The HDR image opens in Photoshop. There is no obvious indication from the image itself that this is an HDR image and not an ordinary photo. However, if you look at the image title bar, Photoshop includes HDR in the name.
12(Optional) Save the HDR image (choose File→Save As).
Photoshop supports many different HDR file types, including the standard Radiance RGBE and OpenEXR formats. You may also choose from any other 32-bits-per-channel format within Photoshop, such as TIFF or PSD. If you choose PDS, though, you might not be able to open these images in other HDR applications.
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